Part 2B

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.

REAR MODE CONTROL MOTOR
Models equipped with the optional rear heater-A/C unit have an electronic rear mode control actuator motor. The two-position rear mode control motor controls the positioning of the heat-A/C mode door in the rear heater-A/C unit housing, and controls the opening and closing of the rear water valve. The rear mode control motor is mounted near the top of the outboard side of the rear heater-A/C unit upper housing, between the horizontal and vertical duct outlets.

The output shaft of the rear mode control motor is keyed to an adaptor, which is keyed to the rear heat A/C mode door pivot shaft. The rear water valve control cable is engaged in a hole on the end of a lever that is integral to the adaptor, and the other end of the cable is secured to the rear water valve control lever. This arrangement links the rear water valve position with the rear heat-A/C mode door position. In the heat position, the rear water valve is open and the rear heater-A/C unit air flow is directed to the left side panel outlets through a horizontal duct. In the A/C position, the rear water valve is closed and the rear heater-A/C unit air flow is directed to the overhead outlets through a vertical duct.

The rear mode control motor is controlled by a momentary electrical switch that is integral to the heater-A/C control. When the rotary-type temperature control knob is moved to a position that is at least 80 percent of its travel from the full clockwise or full counterclockwise stop position, the switch opens or closes the signal circuit for the rear mode control motor to ground. This signal causes the rear mode control motor to switch modes.

The rear mode control motor is accessible for service by removing the horizontal and vertical ducts from the rear heater-A/C unit. The rear mode control motor cannot be repaired and, if faulty or damaged, it must be replaced. The heat-A/C mode door, the rear water valve, the rear water valve control cable and the adaptor are available for service replacement.

REFRIGERANT
The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.

Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.

R-134a refrigerant is not compatible with R-12 refrigerant in an air conditioning system. Even a small amount of R-12 added to an R-134a refrigerant system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance. In addition, the PolyAlkylene Glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.

R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the compressor identifying to service technicians that the air conditioning system is equipped with R-134a.

REFRIGERANT LINES
The refrigerant lines and hoses are used to carry the refrigerant between the various air conditioning system components. A barrier hose design with a nylon tube, which is sandwiched between rubber layers, is used for the R-134a air conditioning system on this vehicle. This nylon tube helps to further contain the R-134a refrigerant, which has a smaller molecular structure than R-12 refrigerant. The ends of the refrigerant hoses are made from lightweight aluminum or steel, and commonly use braze-less fittings.

Any kinks or sharp bends in the refrigerant plumbing will reduce the capacity of the entire air conditioning system. Kinks and sharp bends reduce the flow of refrigerant in the system. A good rule for the flexible hose refrigerant lines is to keep the radius of all bends at least ten times the diameter of the hose. In addition, the flexible hose refrigerant lines should be routed so they are at least 80 mm (3 inches) from the exhaust manifold.

High pressures are produced in the refrigerant system when the air conditioning compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.

The refrigerant lines and hoses are coupled with other components of the HVAC system with peanut- block style fittings. A stat-O seal type flat steel gasket with a captured compressible O-ring, is used to mate plumbing lines with A/C components to ensure the integrity of the refrigerant system.

The refrigerant lines and hoses cannot be repaired and, if faulty or damaged, they must be replaced.

REFRIGERANT OIL
The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, PolyAlkylene Glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.

There are different PAG oils available, and each contains a different additive package. The TRS-105 compressor used in this vehicle is designed to use an SP-15 PAG refrigerant oil. Use only refrigerant oil of this same type to service the refrigerant system.

After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause compressor damage, and too much can reduce air conditioning system performance.

PAG refrigerant oil is much more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After use, recap the oil container immediately to prevent moisture contamination.

REFRIGERANT SYSTEM SERVICE PORT
The two refrigerant system service ports are used to charge, recover/recycle, evacuate, and test the air conditioning refrigerant system. Unique service port coupler sizes are used on the R-134a system, to ensure that the refrigerant system is not accidentally contaminated by the use of the wrong refrigerant (R-12), or refrigerant system service equipment.

The high pressure service port is located on the discharge line between the compressor and the condenser, near the front of the engine compartment. The low pressure service port is located on the suction line jumper, near the filter-drier at the front of the engine compartment.

Each of the service ports has a threaded plastic protective cap installed over it from the factory. After servicing the refrigerant system, always reinstall both of the service port caps.

THERMAL LIMITER SWITCH
The thermal limiter switch is used to measure the compressor surface temperature. If the compressor surface temperature is excessive, the switch will cut the battery feed voltage to the compressor clutch coil. The switch will reset itself, once the compressor surface temperature returns to normal.

The thermal limiter switch will interrupt the battery feed to the compressor clutch coil at a temperature of about 122 - 128 °C (250 - 260 °F). The switch will reset and restore the clutch coil operation at a temperature of about 104 - 116 °C (220 - 240 °F). The thermal limiter switch cannot be repaired, and is not available as a serviceable item. If faulty or damaged, the entire compressor must be replaced.

VACUUM CHECK VALVE
A vacuum check valve is installed in the vacuum supply line in the vacuum harness. The check valve is located near the left end of the distribution duct under the instrument panel in the passenger compartment. The vacuum check valve is designed to allow vacuum to flow in only one direction through the vacuum supply circuits.

The use of a vacuum check valve helps to maintain the system vacuum needed to retain the selected heater-A/C mode settings. The check valve will prevent the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load (low engine vacuum) operation.

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

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.

WATER VALVE
Front
A vacuum-actuated water valve is installed in the heater hose between the engine and the front heater core in the engine compartment. Vacuum to the front heater core water valve is controlled by the rotary type mode control vacuum switch in the heater-only or heater-A/C control.

The front water valve is a normally-open valve used to control engine coolant flow through the heater core. When vacuum is applied to the integral water valve vacuum actuator, the actuator closes the valve and coolant flow through the heater core is stopped. When the water valve is opened (no vacuum is applied), the coolant flows through the heater core and back to the engine.

The front water valve cannot be repaired and, if faulty or damaged, it must be replaced.

Rear
On models equipped with the optional rear heater-A/C unit, a cable-actuated rear water valve is located near the back of the rear unit housing. The rear water valve is installed in the rear unit heater hose between the engine and the rear combination coil. The rear water valve control cable is operated by the rear mode control motor.

The rear mode control motor is controlled by a momentary switch that is integral to the heater-A/C control. When the rotary-type temperature control knob is moved to a position that is at least 80 % of its travel from the full cool position, the switch closes the signal circuit for the rear mode control motor to ground. This signal causes the rear mode control motor to move the rear heat-A/C mode door to the heat position and open the rear water valve. When the switch opens the signal circuit, the motor moves the rear heat-A/C mode door to the A/C position and closes the rear water valve.

The rear water valve cannot be repaired and, if faulty or damaged, it must be replaced.