Control Assembly: Description and Operation

A/C HEATER CONTROL
Both the heater-only and heater-A/C systems use a combination of electrical and vacuum controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. Refer to the owner's manual in the vehicle glove box for more information on the features, use, and suggested operation of these controls.

The heater-only or heater-A/C control is located to the right of the instrument cluster and below the radio on the instrument panel. The control panel contains a rotary-type temperature control knob, a rotary-type mode control switch knob, and a rotary-type blower motor speed switch knob. Models with the optional rear heater-A/C unit have a rotary-type rear blower motor speed switch mounted in the accessory switch plate, which is located to the right of the heater-A/C control on the instrument panel.

Models with the optional rear heater-A/C unit also have an additional momentary electrical switch that is located within the heater-A/C control. This switch is operated by a cam mechanism that is driven by the temperature control knob. The switch opens and closes a circuit to ground in order to signal the rear mode control motor to change modes. The rear mode control motor controls the rear heat-A/C mode door and the rear water valve. When the temperature control knob is moved to at least 80 percent of its travel from the full counterclockwise (Cool) position, the rear heater-A/C unit is switched to the heat mode and the rear water valve is opened; and, when the temperature control knob is moved to at least 80 percent of its travel from the full clockwise (Warm) position, the rear heater-A/C unit is switched to the A/C mode and the rear water valve is closed.

The heater-A/C control unit cannot be repaired. If faulty or damaged, the entire unit must be replaced. The incandescent illumination lamps are available for service replacement.

REAR A/C HEATER HOUSING
Rear Heater And Air Conditioner
An optional rear heater and air conditioner unit is available on 127 inch wheelbase and extended 127 inch wheelbase models with the optional front air conditioner, and operates in conjunction with the front heater and air conditioner. This unit consists of a blower motor, a thermal expansion valve, a cable-actuated rear water valve, a combination coil unit, and an electronic rear mode control actuator motor that operates a rear heat-A/C mode door and the rear water valve. The rear heater and air conditioner unit is contained in a housing mounted to the floor panel in the passenger compartment between the fuel filler inlet housing and the rear wheel housing near the left rear side panel. A trim cover is mounted to the unit.

The rear heater and air conditioner unit recirculates and conditions the air in the vehicle. The electronic rear mode control motor operates the heat-A/C mode door in unison with the rear water valve. This ensures that when the unit is in the heat mode (water valve is open), the conditioned air is directed through a horizontal duct to outlets in the left side panel lower trim; and, when the unit is in the A/C mode (water valve is closed), the conditioned air is directed through a vertical duct to an overhead duct and outlets integrated into the rear headliner.

The rear heater plumbing is connected to the front heater plumbing; and the rear air conditioner plumbing is connected to the front air conditioner plumbing. A thermal expansion valve on the rear heater and air conditioner unit controls refrigerant flow to the combination coil.