Is it ever OK to run the AC along with the heat?

Dear Car Talk

Dear Car Talk | Apr 01, 1996

Dear Tom and Ray:

I just bought a four-cylinder 1995 Plymouth Acclaim. The salesman told me to put the temperature controls on "air-conditioning" in the winter when I want heat instead of on the "heat" setting. He says that I'll get just as much heat and will prolong the life of the air conditioner. I can get heat when I use the air-conditioner setting, but I don't see anything listed about this in the owner's manual. Do you recommend this procedure? -- Victoria

TOM: No, we don't. I'm going to have to amend my theory of misinformation, Victoria. I used to think that 99 percent of all misinformation in the world was passed down by fathers. But I'm going to have to change that. Let's say 90 percent fathers, 9 percent salesmen, and the rest is from us.

RAY: The only time we suggest running the heat and air conditioner simultaneously is when you're trying to defog the insides of the windows.

TOM: The air conditioner does two things. It reduces the temperature of the air and it removes moisture from the air. That removal of moisture is the "conditioning" in air conditioning.

RAY: And when you've got moisture on the inside of your windows, like you do when the air is particularly humid (like when it's raining, snowing, or when you've got a 140-pound Bernese mountain dog panting in the passenger seat), removing the moisture (with air conditioning) helps you clear those windows a lot faster.

TOM: But if it's winter, and you just use the air conditioner, you're going to have icicles hanging off your ears before long. So that's when we recommend you use both: the air conditioner to remove moisture from the air and the heater to warm the air so you don't freeze your tootsies off. And in fact, many cars turn the air conditioner on automatically when you switch the "defroster" on.

RAY: It doesn't do any harm to use the air conditioner and heater all the time, but it's unnecessary and somewhat wasteful. First of all, the salesman is wrong about getting just as much heat. You're not getting the maximum amount of heat because the air IS being cooled off prior to being heated. And second, your gas mileage will suffer because it takes energy to run the air conditioner.

TOM: The salesman's concern about prolonging the life of the air conditioner is legitimate. He's concerned about the seals in the compressor drying out over the six months of winter when the a/c isn't being used. But using it occasionally -- even once a month or so -- to defrost the windows should adequately address that concern.

* * *
TOM: Hey, do you think you're taking good care of your car? Are you sure?

RAY: If you're like many of our customers, you may be RUINING YOUR CAR WITHOUT EVEN KNOWING IT. Yes, even you! Find out how. Send for your copy of our informative pamphlet, "Ten Ways You May Be Ruining Your Car Without Even Knowing It!"

TOM: Send $3 and a stamped (55 cents), self-addressed, No.10 envelope to Ruin No.1, PO Box 6420, Riverton, NJ 08077-6420.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One