For 1990-2009 cars

The A/C system delivers cooled or dehumidified air for occupant comfort. The A/C system also provides power ventilation, windshield and side window defrosting.

During most operating conditions, the blower motor draws in outside air through the heater, ventilation and A/C (HVAC) module. The forward movement off the vehicle forces in additional outside air.

Within the HVAC module, air is forced through the evaporator, through the heater core depending on the LH and RH temperature valve position, then into the passenger compartment. For A/C or defroster operation at ambient temperatures above 7°C (45°F), the refrigeration system will chill the evaporator to almost freezing. As the air passes through the evaporator, the air temperature drops, causing the moisture in the air to condense and accumulate on the evaporator core fins. A gravity feed drain hole removes the moisture from the vehicle, thus dehumidifying the air.

From the evaporator, some or all of the air may pass through the heater core where the engine coolant warms the air if in the heating mode.

When selecting the maximum A/C RECIRC mode, most of the air entering the blower motor is from the passenger compartment where the air is most likely to be cooler than the outside air. Outside air is used exclusively in all other modes.

In the maximum A/C mode, engine coolant is cut off from entering the heater core by the heater water valve to provide optimum cooling efficiency.