Air Conditioning Use Question

engines

#1

Whenever my wife and I use AC in our car, I turn it off before shutting the car off and always make sure it’s off for starting the car. I do this because it is my opinion that it reduces the initial load on the engine when starting it up. I admit that it’s probably a minor difference, but feel it would add up over time. Turning it on and off drives my wife nuts, so I told her I’d put it on here to see what other people think. If there’s more support for leaving AC on, then I lose and have to leave it on. If the support is in my favor, then I get to continue. Share your thoughts. Please share any evidence for it or against it you may have.


#2

A better idea yet is to turn the compressor off a few minutes before turning the blower off,this inhibits bacterial growth.

The “load on engine” line of thought is so oldschool.


#3

The AC compressor is not engaged until after the motor has started even if the dash controls for the AC are on. The way the car is wired puts all the electric current goes to the starter. While the starter is cranking the motor all the accessories are shut off, including the AC fan, until the motor is running.

Therefore your practice isn’t helping anything and isn’t harming anything either. I vote to leave the AC on.


#4

If you turn on your headlights before you start the car, you will notice that they automatically shut off when you turn the key. That is because the car automatically cuts power to the accessories when you turn the key, and that includes the air conditioner.

I know old habits die hard, which is why I turn my air conditioner off, but your wife wins and you lose. Get used to it.


#5

If you have a hybrid car, then you don’t have to worry about this. Even if you don’t, you still don’t need to worry.


#6

Well, I’m officially proven wrong here. My wife thanks everyone for their information. The AC will remain on when the weather calls for it.


#7

Yep, you’re wrong. As others have said, all accessories are off while starting a car. You don’t need to turn off anything. (radio, wipers, air vents etc.)


#8

None of my cars do this…


#9

I assume you refer to the headlight cut off. None of mine do this either. In fact, they automatically turn the headlights on (if it’s dark) when I turn the key on. They remain on while starting. The starter is a 300 + amp load. The headlights are only 10 amps for both. It’s not enough more load to need to turn it off. (My wife had an import that did do this.)
The AC compressor on most 1990 and later cars is not only turned off during starting, but is also kept off until some delay after the engine has reached normal idle RPM (or higher).


#10

What you are doing is probably good. I believe it is good to go easy on machinery. I always seem to forget to turn the AC off.


#11

The relay that energizes the clutch circuit and engages the compressor is not energuzed in the “start” position. The cutch is not engaged until you let go of the key and it drops back to the “on” position.

But I too have heard what Oldschool suggests, that allowing the evaporator to dry some before shutting the car down by turning the AC off at the last miles of the trip prevents a moist host environment for bacteria and prevents that “musty” smell from developing. I don’t know if it’s true, but I’ve been doing it for a few years now.