Using Automotive A/C Q & A

(1) Is it bad to run an automotive air conditioner when it’s cold out?

Running the a/c in the winter months does not cause any harm to the car’s heating and cooling system. In fact, there are many benefits to running the car’s air conditioning in the winter:  it helps dehumidify the air, reducing window fog and it keeps A/C systen and its components active, keeping the owner aware of any potential issues while they’re still small.

(2) It is okay to start a car with the A/C running?

When the starter motor is engaged the A/C clutch is disengaged and any non-essential electrical loads are automatically turned off until the engine is actually running. Therefore, it actually makes no difference whatsoever.  In fact, you may actually help preserve your air conditioning system vs the alternative of turning it on when the car is cruising down the highway at 60 mpg.

(3) Does running the A/C reduce gas mileage?

Studies have shown that using the A/C in your car does lower your car’s fuel efficiency by an average of 3 miles per gallon . A/C lowers your fuel efficiency because it diverts  energy from the engine to power the car. The fuel to power the A/C has to come from somewhere, and the engine is the most efficient way for the A/C to get its energy.  However, if you’re driving at high speeds, leaving your windows down can actually lower your fuel efficiency MORE  than using your A/C would. Lowering your windows can lower your fuel efficiency because the wind entering your car creates a drag that forces your car to work harder to get to the same speed if the windows were rolled up.

There is no method to cool your car that doesn’t lower your car’s fuel efficiency. Choose the method that makes you the most comfortable while driving.

(4) Can I run my A/C with my windows or sunroof open….or my top down?

Sure…..(but why would you want to?) running the A/C with the top down would not maximize the benefit of your air conditioner.    With that said, it wouldn’t harm you’re A/C system at all.  Your system would put forth the same amount of effort whether your windows are open, you top is down, or not.

(5) How long can I leave the A/C on if my engine’s not running?

You actually cannot run the AC without the engine running. The air conditioner compressor and clutch are operated by the same serpentine belt that runs your engine accessories.  If the engine isn’t running, then the belt isn’t turning. That means your air conditioner is not actually on, although the blower may be running and recirculating the air.   As long as your battery is charged, and your key is set to “accessory”, you may be able to run the blower for a while.  Just don’t run it so long that you deplete the battery.


LMK 2020