Turn off AC a few blocks before turning off car?

I am stuck from the old days turning off ac a few blocks before I stop the car. Good idea, bad idea, or irrelevant?

IMHO, a good idea. I like to do this because it allows the evaporator to drain condensate and dry out. You will still get cool air as the evaporator warms up. This procedure seems to help with the occurance of mold and the musty stale refrigerator smell.


I turn it off a little ways before stopping, then let the fan continue a bit. Both are shut off before parking. I have no idea if it’s in any way beneficial, but it feels like I’m doing well by my car.

Irrelevant. I let my automatic transmission shift on it’s own as well.

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Harmless. It matters not to the system.
But if it helps you sleep better, there’s also no reason to discontinue the practice.

While condensation does form on the evaporator as the warmer, moisture-laden cabin air’s heat is transferred through the vanes’ surfaces and into the refrigerant, and turning it off early would allow that condensation to dry some, I think it’s overkill. I’ve never heard of a system component failure from putting the system to bed wet. The materials the system is comprised of are intentionally selected and treated to resist oxidization.

And in every car I’ve ever owned I think the AC compressor circuitry includes a relay that allows the system to shut itself down when you turn the engine off, so there’s no worry about the AC compressor adding to the starter motor’s load upon starting the engine again. The compressor clutch circuitry is only enabled when the engine is running.

By the way, there may be cars out there that don’t turn the AC system off automatically, so on that point I’m open to the knowledge of others. Besides, I never use AC, I use 4-40… (4 windows open and 40mph). So my in-depth knowledge of it may be lacking. :smiley:

Not gonna do that here, I prefer the a/c. And I’ve had no problems in 20 years in Dallas.

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Maybe years ago but not worth the effort now. I can hear my wife now if I started doing that.

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I’ve long shut the AC off about a minute before my destination in order to save a little wear&tear and not have it producing cold air I’m not going to benefit from.

Besides, I never use AC, I use 4-40… (4 windows open and 40mph). – mountainbike

Wow I’d think you’d have some mighty unhappy passengers at times.


VOLVO V70: I remember turning off A/C prior to vehicle shut down 30+ years ago.

If I have passengers, I configure the car for their comfort. Unless there’s someone in the back seat, they’re usually happy with 4-40. In my case I open the roof too, so you might say it’s 5-40. :smile:

My wife prefers open windows driving in the city.
That’s basically end of story for that situation. :smile:
Since virtually every trip on the highway begins and ends with some urban travel for us it’s automatic that AC gets turned off before shut down.

Irrelevant. My car drains a little water on the garage floor, and I don’t think it would change much if I turned the AC off as I turn into the neighborhood. I just let the climate control do its thing.

Irrelevant…condensation will flow out through drain tubes (water puddle under your car after you park) and moisture inside the a/c lines will be absorbed by the inline dryer/filter as the gasses flow through the lines. The drop of gasoline you save by shutting it off a block before you park the car is irrelevant.

I switch off the compressor two blocks from home during the hot months to expel some of the heat from the engine compartment. Irrelevant to others.

I’ve never done it, and haven’t had any problems with the A/C in any car I’ve ever owned. I’ve heard of people making sure that the A/C was turned off before starting their car. Seemed like a frivolous practice to me.

One of the many ways we can obsess about the complex machinery that is our car. I do it when I’m driving my Miata, but it’s because the last half mile is up a very steep hill and the extra drag of the compressor makes me use second gear. Without the AC I can use third, and the ride is more relaxed. On my wife’s car I don’t bother.

This seems like behavior that had benefits decades ago, but today’s cars are equipped with systems that I think make such behavior redundant.

Yes must be a carry over from the early days, I remember some comedians bit, the brakes were so lousy in this car if he needed to stop fast he would turn on the ac!

I think it is probably irrelevant today also as wife never turns off the ac memorial day to labor day, I think in early versions of ac it was recommended, but I have trouble stopping myself from doing it.

Actually filled up at a gas station in the middle of nowhere while the tanker truck was there, crossed fingers and hoped everyone was right, but still will go to another gas station if available.

I suppose it might be genetic, Grandmas sister who grew up with gas lights in the house thought something needed to be plugged into every electrical outlet, or electricity would spew out. On we go.

In the motor pool where I work, we have a diesel bus that, according to the owner’s manual, should have the a/c shut off before starting the vehicle. I’ve forgotten to do it a couple times, and the vehicle doesn’t appear to have suffered from it.

Cabin filters make all the difference. Old cars that didn’t have them would get dust buildup inside the vent passages. Running the air conditioner would make the vents cold, and then when you shut the car off the cold vent would condense moisture out of the air. That moisture wouldn’t dry up as fast because of the dust, and the dust would in part be made up of organics, so mildew would form and smell bad.

Now that cabin filters are pretty much ubiquitous in newer cars, you can have over 100k on the car and still have nice, clean vent passages, which lets the condensed moisture evaporate and does not provide a growth medium for mildew to begin with.