Important: Review the precautions on handling Refrigerant-134a (R-134a) and the information on discharging, recovery and recycling procedures, prior to performing any work on the air conditioning system. Refer to Handling Refrigerant R-134a and Refrigerant Recovery and Recharging .

The A/C switch controls the operation of the air conditioning system. The A/C switch is mounted on the heater control unit. In all modes, the A/C switch must be in the ON in order to engage the compressor. When the A/C switch is pressed, the switch signals the A/C compressor control module that air conditioning system operation has been requested.

The air conditioning system delivers air that has been heated, or cooled and dehumidified for occupant comfort. The air conditioning system provides ram air, power ventilation, windshield defrosting, and side window defogging.

During most of the air conditioning system operating conditions, the blower draws fresh outside air into the ventilation ducts. Additional air (ram air) is forced into the vehicle by the forward movement of the vehicle.

Within the ventilation ducts, the blower motor pushes the air through the evaporator, then through the heater core, and into the passenger compartment. The refrigeration system chills the evaporator to almost freezing for the air conditioning or defroster operating modes. As the air passes through the evaporator, heat in the air transfers to the evaporator core. This heat transfer causes the refrigerant in the evaporator core to vaporize and the air temperature to drop. The decreased air temperature causes moisture in the air to condense on the evaporator core fins. The moisture leaves the vehicle by gravity feed, through a drain hole, dehumidifying the vehicle.

From the evaporator case, some or all of the air may pass through the heater core, depending on the position of the temperature control. The air that bypassed the heater core mixes with the air that passed through the heater core and then enters the passenger compartment.

Set the fresh/ recirc control lever to recirculation for the maximum air conditioning. Most of the air entering the blower during this mode is taken from the passenger compartment (recirculated), where the air is likely to be cooler than the outside air.

The A/C switch may be turned to the OFF position in order to turn off the A/C system during the heater-only mode or the ventilation mode. The degree of heating is determined by the proportions of the air directed through or around the heater core, in the same manner as the air conditioning system. The heater control unit assembly in the instrument panel provides the means for selecting the desired operating mode, the air temperature, and the blower speed when the engine is running.