Your car's engine is the power source for both heating and air conditioning systems. The systems also share other components, as the following diagram shows. Here's what happens when you flip on the heat or the air conditioner:
Heat is a byproduct of the engine's combustion process. The heat is absorbed by the coolant in your car's radiator. The coolant is then circulated through the heater core before returning to the radiator. The heating system also includes a series of air ducts, a blower motor and fan, and temperature and duct controls, which selct the desired temperature and direct the flow of warm air.
This is a pump that pressurizes and circulates the refrigerant through the system.
As the refrigerant flows through the condensor, it gives up heat and converts from gas to liquid.
This is where clean, dry refrigerant is stored as it circulates through the system.
This is a metering device that controls the flow of refrigerant through the system.
Refrigerant enters the evaporator core as a liquid. Heat from the air converts the liquid refrigerant back into a gas, which cools the air before it enters you car.