CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

A/c or no a/c

my boyfriend always runs his air conditioner thinking it actually conditions the air and makes it better. the a/c is never turned off and runs even when the heater is on. i think this is a waste of fuel and he would get better mpg if he only used the a/c to cool the car. who is right, please?

The a/c dries the air, hot or cold. It does not improve it’s quality or cleanliness. He would improve his fuel economy a little by not running the compressor all the time. It is wrong to think that running the a/c all the time is better.

I didn’t even know one could run a/c and the heater at the same time. (In my car you cannot do that). A/c does not actually filter the air, it merely makes it colder and drier. Though todays air conditioning systems are vast improvements over the 1990’s versions he will get better mileage by turning it off.

The only positions the A/C compressor does not operate in is VENT and HEAT. Run the defrosters in the winter and the A/C compressor will be operative.

How does your boyfriend operate the compressor when the mode control is in the HEAT position?

Neither of my cars have a “heat” position. But you can turn the temperature to hot, and run the a/c and you can get hot dry air coming out of any of the vents.

In those cars that allow it, and in areas where the humidity is high, it certainly can make it more comfortable. It will reduce mileage, but not all that much and I would rather be comfortable.

BTW most if not all cars will run the AC anything the deforst is turned on.

In addition to cooling the AC should always be used when your windows are fogging whether mid winter or summer. The heat setting is irrelevant.

My wife’s Subaru automatic climate control system appears to have AC compressor running or at least light on 95% of drive time including coldest day on winter.

Oh. Not mine. Then again, most people drive cars that are probably better designed/ 10 years newer than my own.

There was an article in this morning’s paper concerning tricks to save gasoline. This is not one of them. Using AC is about the same as not using AC. Your BF is correct about cleaning the air if the alternative is open windows if the car has a cabin air filter.

I have GM cars and use the AC pretty much all the time because of the humidity. Occasionally it will be too cold blowing on me so I add a little heat and adjust it to my comfort level. Dunno what I’d do without this feature. I agree, most people are unaware they can do this.

Well, he’s not hurting anything, and if it’s his car and he’s paying for the fuel, I’d just let it go.

A/C units have become much more efficient in recent years to the point that there is really no effect on fuel economy.

Running the a/c will not “condition” or improve the air but in some models (Fords) that do not have a recycle inner air setting, the Max A/C setting is the only way to accomplish this which may be what your boyfriend is thinking. Recycling inner air essentially blocks a higher percentage of outside air from coming so you won’t breathe outside exhaust in heavy traffic, etc…

he might be lucky to get 1 mpg improvement if he didn’t, but is that 1 mpg really worth being uncomfortable?

Cooling air and then re-heating it is a standard way of reducing humidity in commercial buildings. It is a smart thing to do in cars too. Don’t nag your boyfriend.

If the boyfriend’s car is equipped with a cabin air filter and he has allergy problems running the AC all the time keeps the windows closed and will keep more dust and pollen out of the air inside the car.

AC does take power off the motor, but at interstate speeds the air turbulence of open window creates more power robbing drag on the car than running the AC. So on the open highway advantage AC over open windows.

In the winter running the AC with the windows closed may hurt gas mileage slightly. The AC compressor cycles on and off as needed and doesn’t run as much in cooler weather as in summer heat.

Bottom line is that it is pretty much a wash. I don’t run the AC much in cool weather, but if my wife did I’d save my argument quota for something more important.

thank you everyone for your input. for the record, i do not nag my boyfriend about this and i even told him he was right to run the a/c. sometimes it’s just abouyt curiosity and not all women fall into a “nag” category. thanks!