So my son is driving his first car, our 2005 Volvo V50. It is winter and he insists on having the AC on along with the heat. I am thinking this is ridiculous and not necessary. The AC for cooling I assume draws off the engine and reduces efficiency. Certainly not needed when the call is for heat. Any confirmations?

Andy

 

Running the AC all the time dehumidifies the interior - preventing (in most cases) the windows from fogging up on the inside. The AC compressor turns on automatically (above x temp) and the recirculate flap is open for fresh air when the front defrost is selected also.

 

The A/C compressor also runs anytime the front windshield defroster is activated. As the previous reply stated, having the A/C compressor on de-humidifies the incoming air which is particularly useful when there is precipitation or fog.