Dear Car Talk,
My stepdad has a rule that the AC should be turned off everytime you turn the car off. That way when the car is started next time, the starter has less work to do, therefore saving wear on the part. So my question is does the AC put more wear on the starter, or more wear on my finger from turning it on and off all the time?
Thank you very much.
Brian.
Not much, if any, extra wear from having the AC on. Many cars disconnect it when starting. But if it makes him happy, why not?
Thanks for the reply. Yeah i figured the parasitic drag is too minor to affect the life of the part. If it can handle turning a V8 thousands of times, it should be able to handle it with AC. And i will be making him happy by obliging, i just want to know if i can add it to the large list of unnecessary unlogical rules 
The circuit that energizes the AC compressor clutch is not enabled in the “start” position in most modern cars, only in the “on” position.
However, if your stepdad has that rule, you should respectfully obey it. When you buy your own car you can do as you please.
A/C compressors have an electric clutch that disengages it from the drive pulley. The pulley spins free during start up. Once the engine is running, the clutch will engage (if the A/C was left on).
Twotone
This is not an unnecessary or illogical rule. The logic is that the AC compressor will put more load on the driveshaft and thus more strain on the starter motor. The fact that it doesn’t (see my other post) does not mean the rule is illogical.
And it is necessary for two reasons.
(1) it’ll give your stepdad confidence that you’ll respect his rules and that will enable him to confidently continue to allow you to use his car.
(2) that same confidence that obeying this rule gives him will carry over into other important requests you’ll have of him.
Life is full of rules that we may not agree with. Part of growing up is learning that many of them need to be obeyed.
Or you could always walk.
Great reply - so true.
If the AC is in fact not engaged on this vehicle during startup then i find it an illogical and unnecessary rule that can be added to my list. And i said i would stay obliged to it. This is just for my knowledge, not on how i act on it.
You could add that this practice is adding unnecessary wear to the switch. (Of course, not enough to cause failure.) I consider some of these practices such as turning off the radio before turning the car off to be about as silly as superstition.
No having the AC on does not increase wear on the starter. I realy do hope that your relationship with your stepfather can get better. Perhaps if you keep a mind set that parents don’t always know what is best for persons placed under their control you can weather this storm and come out of it with a personality that allows you to get along with others. When a parent resorts to the line"while you live under my roof"… well the situation has degraded quite severly.I certainly hope that the abuse stops at this level but I certainly am not trying to minimize what you must endure, good luck.
I turn my AC off a few minutes before I park my car, but it is health rather than a mechanical concern. The moisture of the air condenses on the cold part of the AC system. It is a cold, wet, and dark place where mold thrives. You don’t want to be breathing in that nasty stuff.
I feel it’s a reasonable question for cars some years ago. But now with computer controlled systems, which by the way contribute parasitic drag all the time, it’s irrelevant. If you leave it on, the computer will decide.
I have climate control (04 4runner) which leaves the AC available all the time when engaged…the computer’s in charge of starting protocol, not me. I turn the key to suggest my intent, the computer’s decides the best way to go about it. Most newer cars are leaning that way IMO.
BTW, step dad can have any rules he wants that are “safe” and involve his cars.
Try watching to see if the compressor turns while the engine is being started. Chances are that it won’t turn. It will engage shortly after the engine starts.
Did you have a rough childhood oldschool?
Just wondering how you divined the state of the OP’s relationship with his step dad?
My dad had the same rule and I got along with him just fine.
Actually, on the OP’s Yukon, the AC clutch is controlled by the PCM. It will not engage while starting. It will only engage after the engine has reached idle RPM and is stable. (This only takes a second or two.) The PCM will disable the AC clutch if the engine RPMs go too low or the engine gets too hot.
I wish the OP only the best.
Understood.
In short, your dad is wrong. When the car is starting the A/C compressor and indeed the blower motor for the fan is disabled. You’re not putting any extra wear and tear in it by leaving it on when starting the car.
As others have stated, the a/c clutch circuit is NOT working during starting.
As well as many other things that you just don’t even notice because it happens do fast as you turn the key then let go.
Let’s slow down the action.
The ignition switch has many terminals on it to engage and disengage circuits.
Turning the cylinder slowly you’ll notice the guages, radio, interior lights, wipers, etc come to life as you get to the run position.
Then turn to the start position ,-- NOTICE – the guages, radio, interior lights, wipers, etc turn OFF during the cranking cycle. This includes the A/C clutch and the blower motor too !
Once you’ve cranked over the engine and you release your grasp on the key, the cylinder and ignition switch spring back to the run position and the guages, radio, interior lights, wiper, etc joyously spring back to life once again.
---- Having the A/C on at start-up will only affect a vehicle like my old carbureted 79 pickup that has idle issues when cold. The a/c load AFTER start up drags the idle down too much and I have to play with the accelerator to keep it idling until it warms up. In this case I prefer the a/c off at start up.
This can be a topic of discussion with your step dad as you tell him what you learned about the starting process.
BUT BEFORE YOU DO, Here’s where I agree with the others.
Preface your conversation with the reassurance that when you’re using his vehicle you will gladly do things his way.
Perhaps the OP could simply explain to his stepfather why he is wrong.