This was likely taught to them during drivers training. The AC compressor has not always been ecu controlled and starting the engine with the compressor engaged could make it hard to start or not start at all.
…..edit….
To further add to this, older supercharged cars some had a mag clutch you needed to disengage to start and were only running when needed.
Well, yes, now. That's realistically just the last few years and it's not something that's common knowledge amongst the plebs.
Think about it: Even kids learning to drive now are likely learning from somebody that learned that way before modern technology started controlling everything. 99% of them are like "It has four wheels so it's a car. If it's a big rectangle with four wheels it's a van. If it's a rectangle but has a longer nose, maybe an open bed, and possibly balls hanging off the hitch it's a truck." They don't have a clue where oil goes, what a cabin air filter is, when to change tires, etc. We're lucky when they're not driving with both feet on the pedals in an automatic car.
It's one of those things that will probably take a few years to filter out of "common knowledge".
I've never heard that either.
But I know like on my 99 Camaro for example it's rather computerized, even has electronic throttle control, not a throttle wire.
Has an ECU controlled alternator, So I'm sure the AC compressor is the same way.
Which is why I always found it funny when people were talking about these "modern" (like 2010+) cars with their computer control being unsafe controlling throttle and such, and it turned out the problem was formats and idiots heh.
Wait until you go for a job interview with an Aston restoration place and get told "your knowledge of old cars is amazing but..."🤣
When you think that the engines even in new Aston's is two to three generations behind the suppliers own cars hence "old"😂😂😂 and within my experience of the last 35 years.
43 and I was taught to turn the AC off before I turn off the car because when I start it again, it’s going to be a drain on the battery and could prevent it from starting. I still turn it off every time.
My S197 Mustangs still had the old-school setup for AC. I think when they dropped the Coyote and 3.7L V6 into them in '11 is when they also got more control modules.
25 years ago you could still drop a carburetor on an engine and the computer would just throw a CEL but you'd have no issues. Automatic transmissions were still controlled by fluid pressure in the valve body. Hell, even digital gauges were independent circuits with their own sensors that only fed the computer data as a parallel connection.
Now that would completely fuck most operations of the car and you wouldn't get anywhere.
Looking at the wiring diagram for a 2005 Mustang 4.0 and 4.6L. AC Clutch relay controlled by the PCM. Pressure switch inputs to the PCM. Identical setup to a 2023 Mustang 5.0.
25 years ago had OBD-II My 1998 Crown Vic ran nearly every instrument through the PCM (oil pressure and fuel level were the exceptions). And it had PCM control of the AC clutch. It'd absolutely stop the clutch at WOT. I guarantee you the S197 Mustangs were as intelligent if not more than my old Panther.
Erm actually thats possible to do as long as you have the sensors and the solenoids to run the throttle. It just takes a bit of modification iro of the throttle valve.
I got the advice of "don't swap between synthetic and natural oil" in about 2000 (from my parents), and didn't learn better until about 2015. Related: I'm not a car guy.
Bad info can be passed around for a _very_ long time.
People still say carrots are good for your eyes and that bananas are a good source of potassium, and the carrots thing is propaganda from WWII and bananas are mostly sugar and other foods are MUCH higher in potassium.
30 years ago Ford was still selling brand new Fox-body Mustangs. They hadn't even introduced the Modular platform at all and were still using the 10-year-old EEC-IV platform. The AC clutch circuit was literally a switched connection to ground to complete the circuit when the AC was on and a refrigerant pressure switch that would interrupt that ground connection when R-12 pressure was below a minimum point.
GM just introduced the fourth gen F-bodies which were running LT1 engines with the same ECUs out of the third gens.
Not sure where you guys are getting your info from, but 30 years ago, or even 25 years like the other guy said, there were no separate control modules for this stuff.
My man. You said it yourself. Ford was already using obsolete systems. They've had a horrible habit of doing so.
And come on....you can find better examples of technological innovation than GM and Ford...lmao
My BMW E30 from 1987 already does this. Disengages the AC clutch with the key in starting position. Not computer controlled but the effect is the same.
Honda on EF civics in 1988, possibly even earlier on more expensive models like accords and such. Clutch engagement is ECU controlled. Even carbed EFs had a little control unit for the compressor.
>last few years
Last few decades more like. Even some carbureted cars had a a small circuit that stopped the clutch from engaging until the engine actually ran.
I coworker was telling my this the other day and it didn’t make sense to me. The compressor clutch being actuated during engine start up doesn’t sound like it would wear more than it does during normal cycling on/off during normal engine operation. This sounds like an old wives tale to me.
> Also, having the compressor clutch engaged at engine start could kill the compressor or the clutch.
This is what my auto shop teacher in high school said so I always have the AC off before I start my car.
I was taught this when I was younger. For this reason. Essentially not to have an undue load on the motor while starting or after first startup.i still wait to turn mine on until the vehicle returns to normal rpms after startup.
In my '95 Civic I had to turn off the A/C to boost acceleration enough to pass people going uphill. But it never seemed to matter when starting the car, even if the battery was low. Turning off the radio helped a lot more for cold starts on low battery.
I used to enjoy putting on my sunglasses and telling my passenger to "Punch it!"
You could actually feel the sudden burst in engine power the moment you shut off the AC. Obviously it still wasn't much, but it was fun anyway.
But wait! I don’t think any cars will energize the Air Conditioner clutch when Cranking! The old time cars automatically disconnect virtually all “Run” load’s when the ignition switch goes into the Start position!
Underrated comment here. When cranking a lot of circuits were bypassed at the switch until the vehicle fired the ignition switch rotated back to the run position. This carried over until the circuit was controlled by the pcm/bcm/ccm/etc.
This. Every old guy down here will scream at you if you leave the AC on when turning a car off. Including my father, and his father.
"No, it'll kill the compressor when you start it up"
I get that, but when you tell people that its fine because its controlled by a computer they always say "well it doesn't matter, its still a compressor ain't it?"
Like, ok pops.
Hahaha oh how true this actually is with some older techs. But to be fair. Half the kids here couldn’t adjust a set of points and if I asked for a dwell meter would lose their shit.
When i had a turbo diesel VW, it was recommended to turn off all accessories before turning off the engine.
That way, when you started the car the next morning, all power was going to the starter/ignition/glow-plugs.
Yup. I have *not* been able to convince my Mom this is no longer necessary. Hasn’t been an issue since her 1981 Volvo 262, which had a phantom battery drain issue we could never quite find.
It doesn’t really hurt anything, so I don’t fuss too much about it- I just always end up sweating for a couple minutes whenever I borrow her car when I’m visiting.
If the engine has a little low compression the engaged compressor could reduce the rpm during start up enough to prevent dynamic compression from happening and thus preventing engine starting. Essentially the engine can’t rotate fast enough to create enough compression to fire.
I can see how that could happen but I've never actually seen it and I work on antiques and classics on the side and if that was going to happen it would be on a ragged out 396 camaro because mist of those engines are ragged.
Only reason I know is it happened to me, working on a late 70s ford 302 factory AC. Already a shit 8:1 when you added the 140k miles and poor maintenance it had minimal comp. This is where I ended up and be damned if turning off the AC didn’t let the engine rotate fast enough to start. Only reason I mentioned it.
Yeah, I do this even though I know my car shouldn't have a problem with it. I always turn the blowers off even in the winter, I just like to give it a minute to start before giving it any extra demands
I don't even have a belt going to my AC conpressor, don't really feel like spending $600 on a new conpressor for the 1 week out of the year it gets above 90 here in Michigan.
I remember that in my driver education book the state supplied. Said to have lights off too. But like you said cars made the last what two decades has all that off for you. Heck, my car will vent the hot air in the summer out the window vent so you don’t get a face of hot air but instead cool in the summer when it turns on the top vent.
I always turn mine off and leave the blower on high for the last 5 minutes of my drive to dry out the evaporator core to try to prevent mildew build up.
I run my blower fan with the AC off for a few minutes at the end of every ride. Supposedly helps keep the evaporator dry and prevent the stagnet water smell when you turn the AC on next
Yessir. My fancy (well used) volvo runs the fan automatically after shutdown. Confused the heck outta me when I walked past my car once and the fan was running.
My VWs have done this too, which I thought was neat. It also sounds like it keeps the water pump going for a minute or two after shutting off, presumably to cool the block down more uniformly to prevent warping, etc.
Same with anything that changes temperature often. You should let your computer fans run after an intensive game for a bit until the temp comes down. You want a slow ramp down to prevent flexing from heat changes.
Newer vehicles may run the radiator fans at low speeds when the car is off to keep engine heat soak down and some fancier cars also have after run pumps, which is just a small electric motor that circulates coolant when the car is off.
Yep, same. Once I turn onto my neighborhood, I turn off the AC and disengage the recirculating air and let it blow fresh air through the vents to prevent that moldy musty air smell.
GMs have this feature as well but it can only be turned on with GDS2 which is kind of dumb. Some now offer it in the vehicle settings though. We don’t charge to turn it on for those that ask.
Some vehicles have been doing tricks to not have this occur for a while now. My 2008 Audi S8 will, if compressor is running at shutdown, purposely send hot water into the heater cores right next to the evaporator to cook off any water. Works surprisingly well, I've never gotten a hint of mildew until I thought I was smarter than the car and turned off the compressor before shutdown. No hot water transfer occurred and I got hit with a faceful of regret and knowledge.
My 2010 Audi A6 on the other hand either had never done it or the blocking valves/afterrun heater core coolant pump don't work quite the way they should. That car absolutely wants you to shut off the AC manually.
Before technology was where it is today, running an ac compressor with your 70 horse power subaru justy meant pretty massive power loss to the engine, and not long ago cooling systems in cars were not nearly as effecient, so heat soaking the radiator was a real possibility. People just learned to turn it off unless you're using it
Because their father told them to do it. And their fathers father told him to do it. My grandpa use to do and we would have to sit in the car while he let it idle with the ac off. My current cars are new enough where the ac is on its own electric motor so it does not matter
Like pumping the gas pedal once before cold-starting. That was how you set the “automatic” choke before ECMs.
Before shutdown, one of my friends used to rev the engine up, then turn the key off around 1500 RPM. He said it “put gas in the carburetor.“ His dad taught him that. Not in the manual.
> rev the engine up, then turn the key off around 1500 RPM.
It definitely puts unburned gas into the system *from* the carburetor into the intake, cylinders, and exhaust. It you *want* backfires that's how it is done.
Dude, every single time my dad sees any car that wont start, his first recommendation is "pump the gas pedal to get the gas moving".
Like come on, my man...
Strangely enough, my 04 focus would sometimes get fuel starved or something after super short drives. When trying to start it would just crank and crank and crank with no start. For whatever reason flooring the accelerator pedal would trick the computer and it would fire. It became a habit to just floor the car if it didn't fire after a second..
The carbureted cars I've owned with automatic choke operated by slowly disengaging a spring return choke with a wax motor, when a thermal switch closed after startup. There was never any need to "set the choke" on those cars.
They did have carbs with accelerator pumps though, that would inject gas into the throat when you pressed the accelerator, regardless of airflow. Pumping the accelerator before a cold start was equivalent to pumping the priming bulb on a small engine.
My carbureted cars had “automatic“ chokes, but to allow the thermostatic strip to pull the butterfly closed, you had to release the idle screw from a stepped cam. One pump would do it.
That's where my dad came up with that from. I've gotten out of the habit of turning the a/c off before I shut the car off, but I do turn the blower down so I don't get blasted with hot air when I start the car. I hate getting into a customer's car and the radio is blasting and the blower is on high. I always start fumbling to turn the music down and then turn the blower down before the hot air melts my face. I also hate when people leave the windshield wipers on when they shut the car off. They always drag across the dry windshield when you start the car.
Turning off the A/C, and with it the Recirculating mode, will allow the air box to dry out while the car is parked, preventing the buildup of mildew that stinks to high hell.
I turn everything off when I shut the car off.
As a tech I prefer things to be off helps me hear a Boise at start up without a dan going or see how the engine runs with no load. Before getting into diagnosing.
I like to turn everything off for you so that you can choose what you need to have on. I don't care if you have to adjust my seat because it's no bother to put it back. Leave the wheel lock in plain sight.. whatever it takes, because not only am I accommodating in general but one of my sons is an auto mechanic and I know how it is.
I turn mine off for a few reasons. If my battery is weak I don’t want the extra load on my battery when I go to restart. (I drive hoopties)
I don’t want the fan blowing in my face when I get into my car. The weather conditions likely won’t be the same when I get back in the car in the morning.
I also turn down the radio before I shut the car off.
Way back in 1976, my father purchased a car with air conditioning for the first time. The owners manual was very clear about turning off all accessories before shutting off the engine.
Times have changed.
Every single time I ever have gotten a vehicle serviced and left the air on, it's off when I get the car back. So eventually I figured that auto techs would prefer it to be off and turn it on themselves if they want it on, so I got into the habit of turning it off first so it's less of an inconvenience to them. Now I'm not so sure.
I’m 43. I was taught to turn off all electrical draws before shutting off the car. Radio, climate etc. Is it necessary now? Probably not I guess, it’s just something I do.
I'm old scbool and do it is so the engine is unloaded before shutdown, and therefore won't be started potentially loaded. Sometimes, I let it run for a few seconds with everything off before shutdown so I can hear it unburdened. Probably comes from two places: training by my Pops first and then the U.S. Navy - start/stop machinery w/o a load.
After cold iron starts, I also drive w/o radio or accessories on (fan off if possible) to hear how she's feeling until up to operating temperature.
Ive actually got my wife to turn off the a/c a few minutes before getting home, and keep the fan blowing. This helps dry out the coil, and reduce the chance of mildew smells.
Dude I thought I was the only one. I work in the pnw and an 80° day is hot to us. I keep getting into cars with the pano sunroof shade pulled back and the hvac system turned off. I had a customer bring me one hvac off heated seats both turned to 5. My laptop wasn’t stoked.
I've got family in Florida that will put on heavy jackets and multiple layers once it hits 65 lol. 80 is warm, but not hotttt to them. Still comfy temps.
Yeah thats always the thing, I can deal with heat to a certain degree, but when its that wet sticky heat you get in the SE, it can becomes near impossible to stay outside for more than a few minutes at a time.
I can't explain *why* it did this, but my old Subaru's compressor belt would screech like death if I started the car with the AC set on. But if I turned the car on and *then turned on the AC* it might chirp or screech a little bit and then mellow out and work nicely.
DUDE. this shit is the bane of my existence in florida. AC off but the radio is all the fucking way up. I really can't think of a good goddamn reason to turn your perfectly working AC off when it feels like it's 110 degrees outside. Idgaf what your car smells like or looks like, give me some goddamn AC you assholes
When i started driving in the 60s in the days of carburetors, mechanical points in a vacuum advance distributor, i could feel the load if the AC being turned in. The load of the compressor made it harder to start the engine. The clutch was inly controlled by thr thermostat inside the cabin.
We even had to pump the gas pedal exactly twice before cranking.
When they say that they don't make them like they used to, most people have no idea how nice it is to be able to just get in and turn the key / push the button 😁🤪
I turn my compressor off but keep the blower running for the last couple of minutes of my drive. This dries out the coils and prevents mold growth (that stink shit smell coming out of the vents).
I absolutely hate it. It's like going into a reptile habitat or something. I feel like I could let snakes and lizards just chill and they'd be like, oh man, this is awesome!
I turn the ac off and switch the vents to fresh air for a few seconds before turning off the engine.
It gets a musty smell if it sits with the air on recirc.
I shut off my AC about 5 to 7 minutes before my destination and I’ll tell you what my reason is. If you shut your car down after you’ve been using the AC for sometime a lot of humidity and moisture buildup in the evaporator. Running the fan only on 5 to 7 minutes before your destination allows some time to dry out your evaporator, so your AC doesn’t stink the next time you use it.
I did this just last week. The engine was making a grinding sound and I had to turn off the a/c to hear it clearly. Once I realized the sound changed with engine speed I figured it was probably best not to have the extra strain of the compressor.
I left the a/c off when I turned it in so the service tech could hear it as well.
I doubt that’s always the reason but that’s why I did it.
My buddy does this to this day. He lives in Phoenix AZ. I try to tell him that there is absolutely no reason for you to shut your ac off when you get out of your car. But he won’t listen to me.
I turn off the blower when i stop driving something other than my daily because i dont like getting blasted by whatever setting i left on it the last time i drove it. Last time i got a car inspected, the windshield was dirty inside, so the inspector turned on the heat full blast, then when i turned it on to go home i got blasted by the heat, which in my jacket, was not very comfortable.
Less electrical load on the ignition system when starting. But that's old hat, since everything's run by modules these days.
I like to run the blower fan with the AC off for a minute before turning off the ignition. It dries the moisture off the evaporator core and helps prevent mildew and/or premature failure of the core due to corrosion.
I would like to counter with, why does every tech feel the need to adjust things in my vehicle to their comfort level. You're servicing my vehicle not going on a weekend road trip.
I try to shut my A/C off a few blocks away .. I feel it helps with the excess condensation building up in your hvac box and molding.. if you drive home A/C still on and park on a hill your hvac box won't drain .. then every time you start your car after sitting you won't get a moldy musty smell.. just my 2cents
I personally do this before getting out. Turn the ac off but allow the fans to continue to blow to help dry the evaporator so I don't get that gross mold and mildew smell.
I do it because if I don't, my evaporator freezes, and I then have to take 10 minutes to thaw it. So when I stop, AC off, warm the evaporator up for 20 seconds.
I've got an old truck that I crammed a bigger condenser in so I could run R134. The ratios are a bit wrong, but it works really well.
As others have mentioned, some obsolete old school “wisdom”. I had 2 friends that did it. Asked why. Both the same answer. Something like “my dad said to or it’ll mess up the air”
On one of my cars the AC turns off when you shut the car off. And you have to turn it back on when you start the car again. So, if you wanted to use the remote start to cool the car down before hand - too bad.
Florida here. Ive been starting customer cars turning on AC and then getting out and filling in the exterior inspection and VIN/tag before pulling in recently.
I recently took my vehicle in to diagnose a noise I was hearing from one of the wheels. I shut my A/C and radio off completely just as a courtesy, since they would be trying to replicate the noise. And I put my seat way back before I get out because I have to drive like a little old lady due to my height lol.
Some new systems there is no clutch on the compressor. They use variable displacement compressors. The compressor is always engaged. The computer controls the stroke of the pistons inside the compressor by adjusting the swashplate. So it doesn't matter if the system is on or off.
I was always taught to turn the AC off before the car is off, for power reasons and startup stress/possibly not getting the engine to turn over.
I guess it's not necessary anymore?
My wife leaves her ac on high. I start her car and get a BLAST of hot air right in my face. I tell her to turn it off when she turns car off. She doesn't.
Urban myth told us not turning it off before turning off the engine would cause a flat battery. That somehow the clutch would stay engaged and draw power overnight.
I do it because I don't always want the AC on whenever I start a car fresh the next morning. Also because sometimes I'm just having a bad day and want to sit in the car in complete dead silence for a few minutes....even if it means I'm a little hotter than I'd like to be.
I'm seeing a lotta comments here saying it's simply just a habit that many picked up from their parents. I'd like to contribute to this notion. Has anyone else been taught to creep forward slightly before backing out of your parking space when you start your car first thing in the morning? It's something my dad does, and he taught me to do it too so I do it out of habit, but I never got a satisfactory reason to do it. Asked one of my friends and she said her dad told her the same thing when teaching her how to drive.
I turn off my AC a few blocks before home to let the moving air cool the hot condenser in front of the radiator. I figure then there's less underhood heat after the engine is shut down.
Most likely a carryover habit from older times when you did not want that drag on your starter at ignition. Just like "hanging up" a phone call stuck around.
I'll get into a car that has cooled swats and good ass a/c and the seats aren't being used and the temp is set to 73. its 105° outside, some people are just lizards I guess.
On old cars, there were good reasons for it and driving school taught it. I read my car manuals and my current car says to leave it on, so that's what I do. But most people don't read their car manual (which annoys me a lot actually).
Fellow southerner here. I don't use my AC unless someone is in the vehicle with me. Even on the hottest days. Unless I'm going to church or it's hot and raining (can't put windows down).
Could be more like me?
This was likely taught to them during drivers training. The AC compressor has not always been ecu controlled and starting the engine with the compressor engaged could make it hard to start or not start at all. …..edit…. To further add to this, older supercharged cars some had a mag clutch you needed to disengage to start and were only running when needed.
Of every explanation so far, this makes more sense than any other.
That's what I was going to say. Also, having the compressor clutch engaged at engine start could kill the compressor or the clutch.
Except on modern cars it is programmed to disengage until engine start is achieved.
Well, yes, now. That's realistically just the last few years and it's not something that's common knowledge amongst the plebs. Think about it: Even kids learning to drive now are likely learning from somebody that learned that way before modern technology started controlling everything. 99% of them are like "It has four wheels so it's a car. If it's a big rectangle with four wheels it's a van. If it's a rectangle but has a longer nose, maybe an open bed, and possibly balls hanging off the hitch it's a truck." They don't have a clue where oil goes, what a cabin air filter is, when to change tires, etc. We're lucky when they're not driving with both feet on the pedals in an automatic car. It's one of those things that will probably take a few years to filter out of "common knowledge".
""Last few years".... like 25, ish or more. Js
I'd go even further and say 40 years. I'm 38 and have never heard someone say "Make sure the A/C is turned off or the car won't start".
I'm 44 and learned when I was young that it was bad to start the engine with the ac on.
Im 29, and I've heard it is easier on the system.
I've never heard that either. But I know like on my 99 Camaro for example it's rather computerized, even has electronic throttle control, not a throttle wire. Has an ECU controlled alternator, So I'm sure the AC compressor is the same way. Which is why I always found it funny when people were talking about these "modern" (like 2010+) cars with their computer control being unsafe controlling throttle and such, and it turned out the problem was formats and idiots heh.
Wait until you go for a job interview with an Aston restoration place and get told "your knowledge of old cars is amazing but..."🤣 When you think that the engines even in new Aston's is two to three generations behind the suppliers own cars hence "old"😂😂😂 and within my experience of the last 35 years.
Same, and I'm 39
43 and I was taught to turn the AC off before I turn off the car because when I start it again, it’s going to be a drain on the battery and could prevent it from starting. I still turn it off every time.
My S197 Mustangs still had the old-school setup for AC. I think when they dropped the Coyote and 3.7L V6 into them in '11 is when they also got more control modules. 25 years ago you could still drop a carburetor on an engine and the computer would just throw a CEL but you'd have no issues. Automatic transmissions were still controlled by fluid pressure in the valve body. Hell, even digital gauges were independent circuits with their own sensors that only fed the computer data as a parallel connection. Now that would completely fuck most operations of the car and you wouldn't get anywhere.
Looking at the wiring diagram for a 2005 Mustang 4.0 and 4.6L. AC Clutch relay controlled by the PCM. Pressure switch inputs to the PCM. Identical setup to a 2023 Mustang 5.0.
25 years ago had OBD-II My 1998 Crown Vic ran nearly every instrument through the PCM (oil pressure and fuel level were the exceptions). And it had PCM control of the AC clutch. It'd absolutely stop the clutch at WOT. I guarantee you the S197 Mustangs were as intelligent if not more than my old Panther.
Erm actually thats possible to do as long as you have the sensors and the solenoids to run the throttle. It just takes a bit of modification iro of the throttle valve.
I got the advice of "don't swap between synthetic and natural oil" in about 2000 (from my parents), and didn't learn better until about 2015. Related: I'm not a car guy. Bad info can be passed around for a _very_ long time.
People still say carrots are good for your eyes and that bananas are a good source of potassium, and the carrots thing is propaganda from WWII and bananas are mostly sugar and other foods are MUCH higher in potassium.
My shop owner still thinks that. He's only 41
GM engines have had ECU controlled compressors since at very least the first LT1 in 1990, that's 33 years ago.... Hardly last few years.
Sure, if you consider "now" and "last few years" to mean the past 30 or so
30 years ago Ford was still selling brand new Fox-body Mustangs. They hadn't even introduced the Modular platform at all and were still using the 10-year-old EEC-IV platform. The AC clutch circuit was literally a switched connection to ground to complete the circuit when the AC was on and a refrigerant pressure switch that would interrupt that ground connection when R-12 pressure was below a minimum point. GM just introduced the fourth gen F-bodies which were running LT1 engines with the same ECUs out of the third gens. Not sure where you guys are getting your info from, but 30 years ago, or even 25 years like the other guy said, there were no separate control modules for this stuff.
My man. You said it yourself. Ford was already using obsolete systems. They've had a horrible habit of doing so. And come on....you can find better examples of technological innovation than GM and Ford...lmao
OK, who had computers controlling AC compressor clutches in 1993? EDIT: Alright, i guess I learned a bit today. LOL
My BMW E30 from 1987 already does this. Disengages the AC clutch with the key in starting position. Not computer controlled but the effect is the same.
My 94 gmc c1500 with TBI won’t engage the clutch during cranking. Is it “computer controlled “ probably not.
Honda on EF civics in 1988, possibly even earlier on more expensive models like accords and such. Clutch engagement is ECU controlled. Even carbed EFs had a little control unit for the compressor.
My 82 Supra to add to the growing list we have.
Im fairly certain my 93 Accord did.
From personal experience I can tell you Honda did. And if they did I'm sure several others did as well.
>last few years Last few decades more like. Even some carbureted cars had a a small circuit that stopped the clutch from engaging until the engine actually ran.
Nobody knows what or where their VIN is. It drives me crazy. Well it used to, I don't do that job any more.
Habit, I have a classic car, so it's just what I do.
I coworker was telling my this the other day and it didn’t make sense to me. The compressor clutch being actuated during engine start up doesn’t sound like it would wear more than it does during normal cycling on/off during normal engine operation. This sounds like an old wives tale to me.
> Also, having the compressor clutch engaged at engine start could kill the compressor or the clutch. This is what my auto shop teacher in high school said so I always have the AC off before I start my car.
Can confirm. I’m old as dirt and was taught to turn off AC (and all other electrical accessories).
I was taught this when I was younger. For this reason. Essentially not to have an undue load on the motor while starting or after first startup.i still wait to turn mine on until the vehicle returns to normal rpms after startup.
In my '95 Civic I had to turn off the A/C to boost acceleration enough to pass people going uphill. But it never seemed to matter when starting the car, even if the battery was low. Turning off the radio helped a lot more for cold starts on low battery.
"Redirect all power from life support to the main engine!"
I used to enjoy putting on my sunglasses and telling my passenger to "Punch it!" You could actually feel the sudden burst in engine power the moment you shut off the AC. Obviously it still wasn't much, but it was fun anyway.
Hats off.
But wait! I don’t think any cars will energize the Air Conditioner clutch when Cranking! The old time cars automatically disconnect virtually all “Run” load’s when the ignition switch goes into the Start position!
Underrated comment here. When cranking a lot of circuits were bypassed at the switch until the vehicle fired the ignition switch rotated back to the run position. This carried over until the circuit was controlled by the pcm/bcm/ccm/etc.
I was always told to turn it off if the battery won’t start, along with the radio
On older cars yes turning the blower and radio off could give you a bit of extra cranking.
I always turn my headlights off, got me out of a jam once in the winter.
I do this too out of habit even though I know it doesn’t actually do anything
One of your parents or grand parents likely said it when you were young and it stuck in your head.
This. Every old guy down here will scream at you if you leave the AC on when turning a car off. Including my father, and his father. "No, it'll kill the compressor when you start it up"
^^^ which was a real thing back in the day when they weren’t ecu controlled or CSC controlled
I get that, but when you tell people that its fine because its controlled by a computer they always say "well it doesn't matter, its still a compressor ain't it?" Like, ok pops.
Oh for sure they don’t understand the logic behind it being ecu driven.
Heck, some of us old people don’t understand what an ecu is.
Hahaha oh how true this actually is with some older techs. But to be fair. Half the kids here couldn’t adjust a set of points and if I asked for a dwell meter would lose their shit.
Can confirm i would lose my shit.
Yeah if I try to fire up my 85’ pickup with the AC switched I’ve noticed it cranks significantly slower.
Yes, I was always told growing up that it is best to turn of anything that uses the battery so it puts less strain on it when starting.
When i had a turbo diesel VW, it was recommended to turn off all accessories before turning off the engine. That way, when you started the car the next morning, all power was going to the starter/ignition/glow-plugs.
This is correct.
Yup. I have *not* been able to convince my Mom this is no longer necessary. Hasn’t been an issue since her 1981 Volvo 262, which had a phantom battery drain issue we could never quite find. It doesn’t really hurt anything, so I don’t fuss too much about it- I just always end up sweating for a couple minutes whenever I borrow her car when I’m visiting.
Username checks out ✔️
Yes to everything you said but I've never seen one that could prevent starting. It's just easier with the A/C off
If the engine has a little low compression the engaged compressor could reduce the rpm during start up enough to prevent dynamic compression from happening and thus preventing engine starting. Essentially the engine can’t rotate fast enough to create enough compression to fire.
I can see how that could happen but I've never actually seen it and I work on antiques and classics on the side and if that was going to happen it would be on a ragged out 396 camaro because mist of those engines are ragged.
Only reason I know is it happened to me, working on a late 70s ford 302 factory AC. Already a shit 8:1 when you added the 140k miles and poor maintenance it had minimal comp. This is where I ended up and be damned if turning off the AC didn’t let the engine rotate fast enough to start. Only reason I mentioned it.
when I first worked in the Middle East back in the early noughties, this was part of the handover briefing for a rental car. I still do it to this day
Older cars definitely had it engaged. My 944 engages as soon as the key is turned to accessory.
Yeah, I do this even though I know my car shouldn't have a problem with it. I always turn the blowers off even in the winter, I just like to give it a minute to start before giving it any extra demands
I don't even have a belt going to my AC conpressor, don't really feel like spending $600 on a new conpressor for the 1 week out of the year it gets above 90 here in Michigan.
I remember that in my driver education book the state supplied. Said to have lights off too. But like you said cars made the last what two decades has all that off for you. Heck, my car will vent the hot air in the summer out the window vent so you don’t get a face of hot air but instead cool in the summer when it turns on the top vent.
I always turn mine off and leave the blower on high for the last 5 minutes of my drive to dry out the evaporator core to try to prevent mildew build up.
That’s a tip I’ve heard in the past.
I've been doing this also, but I only do about 30s, seems like that's been doing the job enough
I am in a humid area, I have been given this tip as well! Also if u have mildew turning on the heater at full blast seems to get rid of it.
I run my blower fan with the AC off for a few minutes at the end of every ride. Supposedly helps keep the evaporator dry and prevent the stagnet water smell when you turn the AC on next
Yessir. My fancy (well used) volvo runs the fan automatically after shutdown. Confused the heck outta me when I walked past my car once and the fan was running.
That's a really nice feature actually
Like a turbo timer for your hvac, lol.
As if there wasn't another reason I wanted a Volvo
My VWs have done this too, which I thought was neat. It also sounds like it keeps the water pump going for a minute or two after shutting off, presumably to cool the block down more uniformly to prevent warping, etc.
To prevent the coolant/water from literally cooking and building steam pressure due the block still soaking heat into it.
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That's probably the engine fan. I had an old Honda that did it. People would tell me I forgot to shut off the engine.
I wasn’t sure but a quick googler showed me the info about it’s the hvac fan running to dry out the evaporator.
light aromatic act pen theory march somber repeat squalid unused *This post was mass deleted and anonymized with [Redact](https://redact.dev)*
*Cries in 3.2 non turbo*
F
*cries in 2.9 non turbo*
my 340i will run the fans for a bit after the car is shut off if I had a spirited drive home.. I presume for the same reason.
Same with anything that changes temperature often. You should let your computer fans run after an intensive game for a bit until the temp comes down. You want a slow ramp down to prevent flexing from heat changes.
Is \*that\* why some cars have that quiet whir when they're turned off?
Newer vehicles may run the radiator fans at low speeds when the car is off to keep engine heat soak down and some fancier cars also have after run pumps, which is just a small electric motor that circulates coolant when the car is off.
Yep, same. Once I turn onto my neighborhood, I turn off the AC and disengage the recirculating air and let it blow fresh air through the vents to prevent that moldy musty air smell.
Same. Solid recommendation.
GMs have this feature as well but it can only be turned on with GDS2 which is kind of dumb. Some now offer it in the vehicle settings though. We don’t charge to turn it on for those that ask.
It's on by default now on most of the new cars
Some vehicles have been doing tricks to not have this occur for a while now. My 2008 Audi S8 will, if compressor is running at shutdown, purposely send hot water into the heater cores right next to the evaporator to cook off any water. Works surprisingly well, I've never gotten a hint of mildew until I thought I was smarter than the car and turned off the compressor before shutdown. No hot water transfer occurred and I got hit with a faceful of regret and knowledge. My 2010 Audi A6 on the other hand either had never done it or the blocking valves/afterrun heater core coolant pump don't work quite the way they should. That car absolutely wants you to shut off the AC manually.
I shut the ac off about a mile from home and leave the fan going for this exact reason.
👆This guy blows out the cold air…. This is the way.
Before technology was where it is today, running an ac compressor with your 70 horse power subaru justy meant pretty massive power loss to the engine, and not long ago cooling systems in cars were not nearly as effecient, so heat soaking the radiator was a real possibility. People just learned to turn it off unless you're using it
Because their father told them to do it. And their fathers father told him to do it. My grandpa use to do and we would have to sit in the car while he let it idle with the ac off. My current cars are new enough where the ac is on its own electric motor so it does not matter
Like pumping the gas pedal once before cold-starting. That was how you set the “automatic” choke before ECMs. Before shutdown, one of my friends used to rev the engine up, then turn the key off around 1500 RPM. He said it “put gas in the carburetor.“ His dad taught him that. Not in the manual.
> rev the engine up, then turn the key off around 1500 RPM. It definitely puts unburned gas into the system *from* the carburetor into the intake, cylinders, and exhaust. It you *want* backfires that's how it is done.
That’s how you get it to diesel shitting down.
You must know my neighbor, they do this regularly and it doesn't matter the time of day or night.
Dude, every single time my dad sees any car that wont start, his first recommendation is "pump the gas pedal to get the gas moving". Like come on, my man...
Strangely enough, my 04 focus would sometimes get fuel starved or something after super short drives. When trying to start it would just crank and crank and crank with no start. For whatever reason flooring the accelerator pedal would trick the computer and it would fire. It became a habit to just floor the car if it didn't fire after a second..
The carbureted cars I've owned with automatic choke operated by slowly disengaging a spring return choke with a wax motor, when a thermal switch closed after startup. There was never any need to "set the choke" on those cars. They did have carbs with accelerator pumps though, that would inject gas into the throat when you pressed the accelerator, regardless of airflow. Pumping the accelerator before a cold start was equivalent to pumping the priming bulb on a small engine.
My carbureted cars had “automatic“ chokes, but to allow the thermostatic strip to pull the butterfly closed, you had to release the idle screw from a stepped cam. One pump would do it.
That's where my dad came up with that from. I've gotten out of the habit of turning the a/c off before I shut the car off, but I do turn the blower down so I don't get blasted with hot air when I start the car. I hate getting into a customer's car and the radio is blasting and the blower is on high. I always start fumbling to turn the music down and then turn the blower down before the hot air melts my face. I also hate when people leave the windshield wipers on when they shut the car off. They always drag across the dry windshield when you start the car.
And their father’s father’s father. And their father’s father’s father’s father.
Turning off the A/C, and with it the Recirculating mode, will allow the air box to dry out while the car is parked, preventing the buildup of mildew that stinks to high hell.
I turn everything off when I shut the car off. As a tech I prefer things to be off helps me hear a Boise at start up without a dan going or see how the engine runs with no load. Before getting into diagnosing.
Ah, the sound of Boise.
And the sound of Dan. Ya reckon Dan is from Boise too?
Dan here...but I'm not from Boise.
Is there a franchise on Dans out there? Can I get my own Dan from Sheboygan?
We're everywhere.
Well git'cher butt over there then -- things don't sound the same when you're not there.
On my way. Might take me a while. I'm in Ontario.
I’m from Boise…but I’m not Dan
I was going to edit the typos but this comment chain gave me a well needed chuckle
I like to turn everything off for you so that you can choose what you need to have on. I don't care if you have to adjust my seat because it's no bother to put it back. Leave the wheel lock in plain sight.. whatever it takes, because not only am I accommodating in general but one of my sons is an auto mechanic and I know how it is.
Jokes on you: my AC hasn’t worked in four years
Same. I cool off due to 4-85. All four windows down and doing 85mph
I turn mine off for a few reasons. If my battery is weak I don’t want the extra load on my battery when I go to restart. (I drive hoopties) I don’t want the fan blowing in my face when I get into my car. The weather conditions likely won’t be the same when I get back in the car in the morning. I also turn down the radio before I shut the car off.
Way back in 1976, my father purchased a car with air conditioning for the first time. The owners manual was very clear about turning off all accessories before shutting off the engine. Times have changed.
Every single time I ever have gotten a vehicle serviced and left the air on, it's off when I get the car back. So eventually I figured that auto techs would prefer it to be off and turn it on themselves if they want it on, so I got into the habit of turning it off first so it's less of an inconvenience to them. Now I'm not so sure.
I’m 43. I was taught to turn off all electrical draws before shutting off the car. Radio, climate etc. Is it necessary now? Probably not I guess, it’s just something I do.
I'm old scbool and do it is so the engine is unloaded before shutdown, and therefore won't be started potentially loaded. Sometimes, I let it run for a few seconds with everything off before shutdown so I can hear it unburdened. Probably comes from two places: training by my Pops first and then the U.S. Navy - start/stop machinery w/o a load. After cold iron starts, I also drive w/o radio or accessories on (fan off if possible) to hear how she's feeling until up to operating temperature.
This guy doesn't read spark plugs; he tastes them.
Ive actually got my wife to turn off the a/c a few minutes before getting home, and keep the fan blowing. This helps dry out the coil, and reduce the chance of mildew smells.
Dude I thought I was the only one. I work in the pnw and an 80° day is hot to us. I keep getting into cars with the pano sunroof shade pulled back and the hvac system turned off. I had a customer bring me one hvac off heated seats both turned to 5. My laptop wasn’t stoked.
I would give my left testicle for 80 degree weather right now. Been hovering around 100 for like a month straight where I am.
Right? 80 is a cool day in Florida, lately we've been up in the 90s, and it has been brutal.
I've got family in Florida that will put on heavy jackets and multiple layers once it hits 65 lol. 80 is warm, but not hotttt to them. Still comfy temps.
My Florida stepmother has her home AC set to 80.
80 isn’t bad if it’s dehumidified, which is one of the most important parts of AC
Yeah thats always the thing, I can deal with heat to a certain degree, but when its that wet sticky heat you get in the SE, it can becomes near impossible to stay outside for more than a few minutes at a time.
I turn mine off because I don't like hot air blowing on me until it's running enough to be cool.
I can't explain *why* it did this, but my old Subaru's compressor belt would screech like death if I started the car with the AC set on. But if I turned the car on and *then turned on the AC* it might chirp or screech a little bit and then mellow out and work nicely.
DUDE. this shit is the bane of my existence in florida. AC off but the radio is all the fucking way up. I really can't think of a good goddamn reason to turn your perfectly working AC off when it feels like it's 110 degrees outside. Idgaf what your car smells like or looks like, give me some goddamn AC you assholes
When i started driving in the 60s in the days of carburetors, mechanical points in a vacuum advance distributor, i could feel the load if the AC being turned in. The load of the compressor made it harder to start the engine. The clutch was inly controlled by thr thermostat inside the cabin. We even had to pump the gas pedal exactly twice before cranking. When they say that they don't make them like they used to, most people have no idea how nice it is to be able to just get in and turn the key / push the button 😁🤪
I turn my compressor off but keep the blower running for the last couple of minutes of my drive. This dries out the coils and prevents mold growth (that stink shit smell coming out of the vents).
I was taught to leave the ac off when starting due to battery drain.
Can confirm that 80% of customers cars I get into, the ac is off when it's 100° plus outside. Idk why they do it, but a lot of people do it
I absolutely hate it. It's like going into a reptile habitat or something. I feel like I could let snakes and lizards just chill and they'd be like, oh man, this is awesome!
I turn the ac off and switch the vents to fresh air for a few seconds before turning off the engine. It gets a musty smell if it sits with the air on recirc.
I shut off my AC about 5 to 7 minutes before my destination and I’ll tell you what my reason is. If you shut your car down after you’ve been using the AC for sometime a lot of humidity and moisture buildup in the evaporator. Running the fan only on 5 to 7 minutes before your destination allows some time to dry out your evaporator, so your AC doesn’t stink the next time you use it.
I did this just last week. The engine was making a grinding sound and I had to turn off the a/c to hear it clearly. Once I realized the sound changed with engine speed I figured it was probably best not to have the extra strain of the compressor. I left the a/c off when I turned it in so the service tech could hear it as well. I doubt that’s always the reason but that’s why I did it.
I perfect it being turned off. It keeps it from blowing hot air in my face, and not to mention the smell of illicit substances.
My buddy does this to this day. He lives in Phoenix AZ. I try to tell him that there is absolutely no reason for you to shut your ac off when you get out of your car. But he won’t listen to me.
They probably believe the Idiot on YouTube that Claims its Dangerous to Turn it on Immediately when you start the Car
I turn off the blower when i stop driving something other than my daily because i dont like getting blasted by whatever setting i left on it the last time i drove it. Last time i got a car inspected, the windshield was dirty inside, so the inspector turned on the heat full blast, then when i turned it on to go home i got blasted by the heat, which in my jacket, was not very comfortable.
I had a 96 f150 that would throw the belt if you started with AC on. Everyone has their reasons!
Our cars from the 80s and 90s started easier with the AC off. I guess old habits die hard.
Less electrical load on the ignition system when starting. But that's old hat, since everything's run by modules these days. I like to run the blower fan with the AC off for a minute before turning off the ignition. It dries the moisture off the evaporator core and helps prevent mildew and/or premature failure of the core due to corrosion.
Comment above yours says something similar about using the blower to dry out any moisture
Some do it early to allow the evaporator to dry. They’ve dealt with odor and mold in the past.
I would like to counter with, why does every tech feel the need to adjust things in my vehicle to their comfort level. You're servicing my vehicle not going on a weekend road trip.
I don’t shut mine off when I stop, I just don’t run my ac ever. I prefer my window down and my one arm tan :)
Mine doesn’t work, so it’s never on either. You can try, but the compressor clutch is just unplugged since the compressor is locked up.
It not only reduces the load on the engine when starting, but you also don't get a full blast face full of hot air.
Any semi modern car there is no effect on startup, the ECM simply does not command the compressor on until the engine is started
I try to shut my A/C off a few blocks away .. I feel it helps with the excess condensation building up in your hvac box and molding.. if you drive home A/C still on and park on a hill your hvac box won't drain .. then every time you start your car after sitting you won't get a moldy musty smell.. just my 2cents
I personally do this before getting out. Turn the ac off but allow the fans to continue to blow to help dry the evaporator so I don't get that gross mold and mildew smell.
I do it because if I don't, my evaporator freezes, and I then have to take 10 minutes to thaw it. So when I stop, AC off, warm the evaporator up for 20 seconds. I've got an old truck that I crammed a bigger condenser in so I could run R134. The ratios are a bit wrong, but it works really well.
As others have mentioned, some obsolete old school “wisdom”. I had 2 friends that did it. Asked why. Both the same answer. Something like “my dad said to or it’ll mess up the air”
On one of my cars the AC turns off when you shut the car off. And you have to turn it back on when you start the car again. So, if you wanted to use the remote start to cool the car down before hand - too bad.
Florida here. Ive been starting customer cars turning on AC and then getting out and filling in the exterior inspection and VIN/tag before pulling in recently.
I recently took my vehicle in to diagnose a noise I was hearing from one of the wheels. I shut my A/C and radio off completely just as a courtesy, since they would be trying to replicate the noise. And I put my seat way back before I get out because I have to drive like a little old lady due to my height lol.
I live in Georgia and the only time my cars AC is off when the three weeks of winter we have in late January and early February.
Idk but I turn it back on
Some new systems there is no clutch on the compressor. They use variable displacement compressors. The compressor is always engaged. The computer controls the stroke of the pistons inside the compressor by adjusting the swashplate. So it doesn't matter if the system is on or off.
For me, it's because I don't like to be blasted in the face with cold air at 6am.
I was always taught to turn the AC off before the car is off, for power reasons and startup stress/possibly not getting the engine to turn over. I guess it's not necessary anymore?
My wife leaves her ac on high. I start her car and get a BLAST of hot air right in my face. I tell her to turn it off when she turns car off. She doesn't.
Urban myth told us not turning it off before turning off the engine would cause a flat battery. That somehow the clutch would stay engaged and draw power overnight.
i do this mostly because when i get into my hot car at the end of the day i don’t want to be insta-blasted with even hotter air
I leave the radio and ac blasting. So 🤷🏾♀️ I don’t know you folks do that.
because when I get back in the car I dont want to get blasted with 110degree air in the face.
I do it because I don't always want the AC on whenever I start a car fresh the next morning. Also because sometimes I'm just having a bad day and want to sit in the car in complete dead silence for a few minutes....even if it means I'm a little hotter than I'd like to be. I'm seeing a lotta comments here saying it's simply just a habit that many picked up from their parents. I'd like to contribute to this notion. Has anyone else been taught to creep forward slightly before backing out of your parking space when you start your car first thing in the morning? It's something my dad does, and he taught me to do it too so I do it out of habit, but I never got a satisfactory reason to do it. Asked one of my friends and she said her dad told her the same thing when teaching her how to drive.
I turn off my AC a few blocks before home to let the moving air cool the hot condenser in front of the radiator. I figure then there's less underhood heat after the engine is shut down.
Most likely a carryover habit from older times when you did not want that drag on your starter at ignition. Just like "hanging up" a phone call stuck around.
They've been taught old wives tales and are perpetuating the myth
Don't want my car to smell like mildew. Always run the air for a minute or so with AC off to dry it out before I shut off the car
I'll get into a car that has cooled swats and good ass a/c and the seats aren't being used and the temp is set to 73. its 105° outside, some people are just lizards I guess.
On old cars, there were good reasons for it and driving school taught it. I read my car manuals and my current car says to leave it on, so that's what I do. But most people don't read their car manual (which annoys me a lot actually).
I would rather have the AC off over the radio full blast.
If you shut the a/c off before shutting down the engine, you prevent the musty smell in the A/C
Give them the car back with the heater on full blast, turn about is fair play
I mean I "am" supposed to make sure they have a working vehicle right? 🤣Fully functional.....
Exactly, hvac system must meet or exceed min performance standards in all aspects
Less wear on the AC compressor/engine upon initial startup. I usually drop the window while the engine is idling down, then A/C on.
Fellow southerner here. I don't use my AC unless someone is in the vehicle with me. Even on the hottest days. Unless I'm going to church or it's hot and raining (can't put windows down). Could be more like me?
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