Part 2A

VACUUM RESERVOIR
The vacuum reservoir is mounted in the engine compartment on the right cowl side panel near the speed control servo and below the right headlamp. The right front fender extension panel must be removed from the vehicle to access the vacuum reservoir for service.

Engine vacuum is stored in the vacuum reservoir. The stored vacuum is used to operate the vacuum- controlled vehicle accessories during periods of low engine vacuum such as when the vehicle is climbing a steep grade, or under other high engine load operating conditions.

The vacuum reservoir cannot be repaired and, if faulty or damaged, it must be replaced.

DISTRIBUTION

DISTRIBUTION DUCT
The distribution duct can be removed from the vehicle without disconnecting the refrigerant lines or discharging the refrigerant system. The distribution duct assembly must be removed from the vehicle and disassembled for service access of the floor-defrost door or the floor-panel door.

WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, DISABLE THE AIRBAG SYSTEM BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE, THEN WAIT TWO MINUTES FOR THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE BEFORE PERFORMING FURTHER DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

Examine all of the distribution duct seals for damage. Replace all damaged or deformed seals. Clean all of the upper and lower distribution duct mating flanges prior to reassembly.

Inspect the distribution duct components for damage. Repair or replace any faulty or damaged components as required. Remove any foreign material or other restrictions to air flow.

AIR OUTLETS
Rear Overhead Duct
A rear overhead duct is only used on models equipped with the optional rear heater-A/C unit. The rear overhead duct is integral to the rear headliner. If either the duct or the headliner is faulty or damaged, the rear headliner unit must be replaced.

BLOWER MOTOR
Front
The front blower motor and blower wheel are located in the blower housing in the engine compartment. The blower housing is integral to the recirculation housing, which is secured to the dash panel and the right cowl side inner panel below the heater-A/C housing. The blower motor controls the volume of air flowing through the heater-A/C system by spinning a squirrel cage-type blower wheel within the housing at the selected speed. The blower motor and blower wheel can be accessed for service from the engine compartment.

The front blower motor will only operate when the ignition switch is in the ON position, and when the heater-only or heater-A/C mode control switch knob is in any position, except OFF. The blower motor receives a fused battery feed through the blower motor relay whenever the ignition switch is in the ON position. The blower motor battery feed circuit is protected by a fuse in the Power Distribution Center (PDC). The blower motor relay control circuit is protected by a fuse in the junction block.

Blower speed is controlled by regulating the blower motor ground path through the heater-A/C mode control switch, the front blower motor switch, the blower motor resistor, and the high speed blower motor relay. When the blower motor switch is placed in the highest speed position it energizes the high speed blower motor relay, which then provides a direct ground feed to the blower motor and bypasses the remainder of the blower motor resistors.

The blower motor and blower motor wheel cannot be repaired and, if faulty or damaged, they must be replaced. The blower motor and blower wheel are each serviced separately.

Rear
The rear blower motor and blower wheel are located in the optional rear heater-A/C unit housing in the passenger compartment. The rear heater-A/C unit is secured to the floor panel between the fuel filler inlet housing and the left rear wheel house against the left side panel. The blower motor controls the velocity of air flowing through the rear heater- A/C system by spinning a squirrel cage-type blower wheel within the housing at the selected speed. The blower motor and blower wheel can be accessed for service from the passenger compartment.

The rear blower motor will only operate when the ignition switch is in the ON position. The blower motor receives a fused battery feed through the ignition run relay whenever the ignition switch is in the ON position. The blower motor battery feed circuit is protected by a fuse in the Power Distribution Center (PDC). The blower motor relay control circuit is protected by a fuse in the junction block.

Blower speed is controlled by regulating the blower motor ground path through the blower motor switch, the blower motor resistor, and the high speed blower motor relay. When the rear blower motor switch is placed in the highest speed position it energizes the high speed blower motor relay which then provides a direct ground feed to the blower motor and bypasses the blower motor resistors.

The rear blower motor and blower motor wheel cannot be repaired and, if faulty or damaged, they must be replaced. The blower motor and blower wheel are each serviced separately.

HVAC HOUSING
All vehicles are equipped with a common heater- A/C housing assembly This system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted in the engine compartment, and a common air distribution duct system mounted under the instrument panel. On heater-only systems, the evaporator coil is omitted from the housing.

The air intake openings must be kept free of snow, ice, leaves, and other obstructions for the heater-A/C system to receive a sufficient volume of outside air. It is also important to keep the air intake openings clear of debris because leaf particles and other debris that is small enough to pass through the cowl plenum screen can accumulate within the heater-A/C housing. The closed, warm, damp and dark environment created within the heater-A/C housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the housing with the outside air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during heater-A/C system operation.

Outside air enters the vehicle through the cowl top opening at the base of the windshield, and passes through a plenum chamber to the right cowl side inlet. Air passes through the right cowl side inlet or the recirculation inlet in the right side of the dash panel into the recirculation housing in the engine compartment. A vacuum actuated recirculation air door controls whether outside air or air from the passenger compartment enters the heater-A/C system blower housing on the inboard side of the recirculation housing. Air flow velocity can then be adjusted with the blower motor speed selector switch on the heater-A/C control panel.

The heater and optional air conditioner are blend- air type systems. In a blend-air system, a blend-air door controls the amount of unconditioned air (or cooled air from the evaporator on models with air conditioning) that is allowed to flow through, or around, the heater core. The heater core, the evaporator coil, and the blend-air door are located in the heater-A/C housing. The heater-A/C housing is mounted to the dash panel in the engine compartment on top of the blower housing. A temperature control knob on the heater-A/C control panel determines the discharge air temperature by moving a potentiometer, which operates the electronic blend-air door actuator motor. This allows an almost immediate manual control of the output air temperature of the system.

The conditioned air is directed through an opening in the right side of the dash panel above the recirculation inlet into the distribution duct under the instrument panel. The mode control knob on the heater-only or heater-A/C control panel is used to direct the conditioned air to the selected system outlets. Both mode control switches use engine vacuum to control the mode doors, which are operated by vacuum actuator motors.

The optional air conditioner for all models is designed for the use of non-CFC, R-134a refrigerant. The air conditioning system has an evaporator to cool and dehumidify the incoming air prior to blending it with the heated air. This air conditioning system uses a thermal expansion valve between the condenser and the evaporator coil to meter refrigerant flow to the evaporator coil. To maintain minimum evaporator temperature and prevent evaporator freezing, a fin sensing cycling clutch switch probe is inserted between the fins of the evaporator coil to cycle the compressor clutch as needed.

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.

PLUMBING

Fig. 1 Sanden TRS - 105 Scroll-Type Compressor:

A/C COMPRESSOR
The air conditioning system uses a Sanden TRS-105 fixed displacement scroll-type compressor on all models. This compressor uses an integral thermal limiter switch to protect it from overheating. A label identifying the use of R-134a refrigerant is located on the compressor.

The compressor is driven by the engine through an electric clutch, drive pulley and belt arrangement. The compressor is lubricated by refrigerant oil that is circulated throughout the refrigerant system with the refrigerant.

The compressor draws in low-pressure refrigerant vapor from the evaporator through its suction port. It then compresses the refrigerant into a high-pressure, high-temperature refrigerant vapor, which is then pumped to the condenser through the compressor discharge port.

The compressor cannot be repaired. If faulty or damaged, the entire compressor must be replaced. The thermal limiter switch is only available as a part of a replacement compressor assembly The compressor clutch, pulley, and clutch coil, are available for service.

High Pressure Relief Valve
The high pressure relief valve is located on the rear surface of the compressor housing. This mechanical valve is designed to vent refrigerant from the system to protect against damage to the compressor and other system components, caused by condenser air flow restriction or an overcharge of refrigerant.

The high pressure relief valve vents the system when a discharge pressure of 3445 to 4135 kPa (500 to 600 psi) or above is reached. The valve closes when a minimum discharge pressure of 2756 kPa (400 psi) is reached.

The high pressure relief valve vents only enough refrigerant to reduce the system pressure, and then re-seats itself. The majority of the refrigerant is conserved in the system. If the valve vents refrigerant, it does not mean the valve is faulty.

On new compressor assemblies, a mylar disc is applied to the venting port of the valve. The disc is primarily intended to indicate if the valve has vented refrigerant during operation. A missing or damaged disc does not indicate failure, but is an indicator of abnormal conditions, and should be diagnosed as to why venting has occurred. If the mylar disc has loosened or come OFF, apply a drop or two of refrigerant oil into the valve mechanism through the venting holes. This will prevent salt, dirt, or moisture from affecting the operation of the valve.

The high pressure relief valve is only serviced as part of the compressor assembly and must not be removed or otherwise disturbed.