why does the a/c compressor cycle on and off when the heat is on?

 

The A/C will run in the Defrost position or combination/selection.. The purpose is to dehumidify the air and reduce windshield fogging.

 

ok i know the evaporator runs into the hvac assembly where the heater core is and blower motor but how does it dehumidify?i also know the evaporator takes liquid refrigerant and turns it into a gas,but i still dont understand how it dehumidifys the air blowing across it

 

Because theevaporator core is cold during defrost,, inductedair passing through/over the evaporatorcollects moisture 'just as' an iced glass of liquid will collect or sweat moisture.. Heat is then added to the drier air for the defrost function..