Air conditioner starts working while its switch is off in Defrost mode

Hi there,

I've just bought a secondhand 2000 Mazda 626 Lx in very good condition except for one odd problem: when I try to select the Defroster Air Flow mode (air towards the windshield) the air
conditioner starts working by it-self, even if it's switch is off.

Any suggestions?

Most cars turn on the Air Conditioning compressor any time "defrost" is selected. Helps to de-humidify the air and clear the fog quicker. Of course the Air Conditioner won't run if the air coming into the evaporator is below freezing. If it is not blowing cold air, you can check for refrigerant leaks with a refrigerant leak detector .