Part 2A
FILTER-DRIERA single filter-drier unit is used for both the front-only A/C system, and for the combined front and rear A/C system. The filter-drier is mounted on the right side of the engine compartment in front of the heater-A/C housing. It is located in the liquid line between the condenser outlet and the evaporator inlet. Refrigerant enters the filter-drier as a high pressure, high-temperature liquid.
The filter-drier performs a filtering action to prevent foreign material in the refrigerant from contaminating the expansion valve. A desiccant bag is mounted inside the filter-drier canister to absorb any moisture which may have entered and become trapped within the refrigerant system. In addition, during periods of high demand air conditioner operation, the filter-drier acts as a reservoir to store surplus liquid refrigerant.
The filter-drier cannot be repaired. If the filter-drier is faulty or damaged, if the refrigerant system has been contaminated, or if the system has been left open to the atmosphere for an indeterminable period, it must be replaced.
FIN SENSING CYCLING CLUTCH SWITCH
The fin sensing cycling clutch switch is used on this model to signal the Powertrain Control Module (PCM) to cycle the compressor clutch on and off in order to control the evaporator temperature. Controlling the evaporator temperature prevents condensate water on the evaporator fins from freezing and obstructing air conditioning system air flow.
Fin Sensing Cycling Clutch Switch:
The fin sensing cycling clutch switch consists of a probe and a switch unit. The probe, which is a Negative Temperature Coefficient (NTC) thermistor in a capillary tube, is inserted between the front evaporator coil fins to monitor evaporator temperature. The switch unit contains internal control logic that monitors the input from the probe in order to switch an internal transistor that controls the output to the PCM.
When the fin sensing cycling clutch switch sees a temperature input below about 1.6 °C (35 °F), it signals the PCM to cycle the compressor off. When the temperature input reaches above about 3.9 °C (39 °F), the switch signals the PCM to cycle the compressor back on.
The fin sensing cycling clutch switch can be accessed for service by removing the screws and care- fully lifting the front of the top cover up from the heater-A/C housing. The fin sensing cycling clutch switch is a sealed unit and cannot be adjusted or repaired. If faulty or damaged, the switch must be replaced.
HEATER AND AIR CONDITIONER
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.
HEATER AND AIR CONDITIONER 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 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 % 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 % 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.
HEATER CORE
Front
The heater core is located in the heater-A/C housing, on the right side of the engine compartment. It is a heat exchanger made of rows of tubes and spacers. Engine coolant is circulated through heater hoses to the heater core whenever the front water valve is open. As the coolant flows through the heater core, heat removed from the engine is transferred to the heater core spacers and tubes.
Air directed through the heater core picks up the heat from the heater core spacers. The blend air door allows control of the heater output air temperature by controlling how much of the air flowing through the heater-A/C housing is directed through or around the heater core. The blower motor speed controls the volume of air flowing through the heater-A/C system.
The heater core cannot be repaired and, if faulty or damaged, it must be replaced.
Rear
Models equipped with the optional rear heater-A/C unit have a combination coil located within the rear unit housing.
The combination coil functions as both the rear heater core and the rear evaporator coil.
HIGH PRESSURE CUT-OFF SWITCH
The high pressure cut-off switch is located on the discharge line near the condenser. The switch is screwed onto a fitting that contains a Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The discharge line fitting is equipped with an O-ring to seal the switch connection.
The high pressure cut-off switch is connected in series electrically with the low pressure cut-off switch between the fin sensing cycling clutch switch and the Powertrain Control Module (PCM). The switch contacts open and close causing the PCM to turn the compressor clutch on and off. This prevents compressor operation when the discharge line pressure approaches high levels.
The high pressure cut-off switch contacts are open when the discharge line pressure rises above about 3100 - 3375 kPa (450 - 490 psi). The switch contacts will close when the discharge line pressure drops to about 1860 - 2275 kPa (270 - 330 psi).
The high pressure cut-off switch is a factory-calibrated unit. The switch cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
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 - 4135 kPa (500 - 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 con- served 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 for 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.
HIGH SPEED BLOWER MOTOR RELAY
Front
The front blower motor electrical circuit uses a high speed blower motor relay. The high speed blower motor relay is a International Standards Organization (ISO)-type relay. The relay is a electromechanical device that switches the blower motor to ground, bypassing the remainder of the blower motor feed circuit.
The high speed blower motor relay is energized when the relay coil is provided a ground signal by the blower motor switch, and a battery feed from the ignition switch. When the relay is de-energized, the front blower motor ground feed is routed through the front blower motor switch and the blower motor resistor.
The front high speed blower motor relay is located in the engine compartment, on a bracket that is secured under one of the screws for the top cover on the inboard side of the heater-A/C housing. The high speed blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced.
Rear
The optional rear heater-A/C unit blower motor electrical circuit uses a high speed blower motor relay. The high speed blower motor relay is a International Standards Organization (ISO)-type relay. The relay is a electromechanical device that switches the blower motor to ground, bypassing the remainder of the blower motor feed circuit.
The high speed blower motor relay is energized when the relay coil is provided a ground signal by the blower motor switch, and a battery feed from the ignition switch. When the relay is de-energized, the rear blower motor ground feed is routed through the rear blower motor switch and the blower motor resistor.
The rear high speed blower motor relay is located in a connector that is secured to the back of the rear heater-A/C unit housing in the passenger compartment.
The rear high speed blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced.
LOW PRESSURE CUT-OFF SWITCH
The low pressure cut-off switch is located on the suction line jumper near the filter-drier in the engine compartment. The switch is screwed onto a fitting on the suction line jumper that contains a Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The suction line jumper fitting is equipped with an O-ring to seal the switch connection.
The low pressure cut-off switch is connected in series electrically between the fin sensing cycling clutch switch and the Powertrain Control Module (PCM). The switch contacts open and close causing the PCM to turn the compressor clutch on and off. This helps to regulate the refrigerant system pressure and protects the compressor from damage due to loss of refrigerant and refrigerant oil.
The low pressure cut-off switch contacts are open when the suction pressure is about 48 - 90 kPa (7 - 13 psi) or lower. The switch contacts will close when the suction pressure rises to about 103 - 172 kPa (15 - 25 psi) or above. Lower ambient temperatures, below about -1 °C (30 °F), will also cause the switch contacts to open. This is due to the pressure/temperature relationship of the refrigerant in the system.
The low pressure cut-off switch is a factory-calibrated unit. It cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.