Part 1 of 3
HEATING & AIR CONDITIONINGRefrigerant 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 to 128 °C (250 to 260 °F). The switch will reset and restore the clutch coil operation at a temperature of about 104 to 116 °C (220 to 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.
Fig. 1 Compressor Clutch - Typical:
A/C COMPRESSOR CLUTCH
The compressor clutch assembly consists of a stationary electromagnetic coil, a hub bearing and pulley assembly, and a clutch plate. The electromagnetic coil unit and the hub bearing and pulley assembly are each retained on the nose of the compressor front housing with snap rings. The clutch plate is mounted on the compressor shaft and secured with a nut.
These components provide the means to engage and disengage the compressor from the engine serpentine accessory drive belt. When the clutch coil is energized, it magnetically draws the clutch plate into contact with the pulley and drives the compressor shaft. When the coil is not energized, the pulley freewheels on the clutch hub bearing, which is part of the pulley. The compressor clutch and coil are the only serviced parts on the compressor.
The compressor clutch is controlled by several components: the heater-A/C mode control switch, the low pressure cut-off switch, the high pressure cut-off switch, the fin sensing cycling clutch switch, the thermal limiter switch, the compressor clutch relay, and the Powertrain Control Module (PCM). The PCM may delay compressor clutch engagement for up to thirty seconds. Refer to Fuel System for more information on the PCM controls.
A/C COMPRESSOR CLUTCH RELAY
The compressor clutch relay is a International Standards Organization (ISO) micro-relay. The terminal designations and functions are the same as a conventional ISO relay. However, the micro-relay terminal orientation (footprint) is different, the current capacity is lower and the relay case dimensions are smaller than those of the conventional ISO relay.
The compressor clutch relay is an electromechanical device that switches battery current to the compressor clutch coil when the Powertrain Control Module (PCM) grounds the coil side of the relay. The PCM responds to inputs from the heater-A/C mode control switch, the low pressure cut-off switch, the high pressure cut-off switch, and the fin sensing cycling clutch switch.
The compressor clutch relay is located in the Power Distribution Center (PDC) in the engine compartment. Refer to the PDC label for relay identification and location.
The compressor clutch relay cannot be repaired and, if faulty or damaged, it must be replaced.
A/C 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.
Fig. 7 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 carefully 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.
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.
A/C HIGH PRESSURE 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 to 3375 kPa (450 to 490 psi). The switch contacts will close when the discharge line pressure drops to about 1860 to 2275 kpa (270 to 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.
A/C LOW PRESSURE 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 to 90 kPa (7 to 13 psi) or lower. The switch contacts will close when the suction pressure rises to about 103 to 172 kPa (15 to 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.
BLOWER MOTOR RELAY
Blower Motor Relay
Front
The front blower motor relay is a International Standards Organization (ISO)-type relay. The relay is an electromechanical device that switches battery current from a fuse in the Power Distribution Center (PDC) directly to the blower motor. The relay is energized when the relay coil is provided a ground signal by the blower switch. This arrangement reduces the amount of battery current that must flow through the ignition switch.
The blower motor relay control circuit is protected by a fuse located in the fuse block. When the relay is de-energized, the blower motor ground path through the high blower relay is interrupted.
The front blower motor relay is located in the PDC in the engine compartment.
The blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced.
Rear
The blower motor relay for the optional rear heater-A/C unit is a International Standards Organization (ISO)-type relay. The relay is energized when the relay coil is provided a ground signal by the blower switch. This arrangement reduces the amount of battery current that must flow through the blower switch.
The blower motor relay control circuit is protected by a fuse located in the junction block. When the relay is de-energized, the blower motor ground path through the high blower relay is interrupted.
The rear 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 blower motor relay cannot be repaired and, if faulty or damaged, it must be replaced.
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 beater-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.
BLOWER MOTOR RESISTOR BLOCK
Front
The front blower motor resistor is mounted to the inboard side of the heater-A/C housing in the engine compartment. It can be accessed for service from the engine compartment. It is secured to the housing with two screws and is connected to the headlamp and dash wire harness.
The blower motor resistor has multiple resistor wires, each of which will change the resistance in the blower motor ground path to change the blower motor speed. The blower motor switch directs the ground path through the correct resistor wire to obtain the selected blower motor speed.
With the blower motor switch in the lowest speed position the ground path for the motor is applied through all of the resistor wires. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed. When the blower motor switch is in the highest speed position, the blower motor resistor is bypassed and the blower motor receives a direct path to ground through the high speed blower motor relay.
The front blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.
Rear
The optional rear heater-A/C unit has a blower motor resistor mounted to the inside of the unit lower housing in the passenger compartment. It can be accessed for service through the horizontal duct opening in the rear heater-A/C unit upper housing. It is secured to the inside of the lower housing by two mounting tabs and a snap feature that are molded into the lower housing, and it is connected to the rear heater-A/C unit wire harness.
The blower motor resistor has multiple resistor wires, each of which will change the resistance in the blower motor ground path to change the blower motor speed. The blower motor switch directs the ground path through the correct resistor wire to obtain the selected blower motor speed.
With the blower motor switch in the lowest speed position the ground path for the motor is applied through all of the resistor wires. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed. When the blower motor switch is in the highest speed position, the blower motor resistor is bypassed and the blower motor receives a direct path to ground through the high speed blower motor relay.
The rear blower motor resistor cannot be repaired and, if faulty or damaged, it must be replaced.
BLOWER MOTOR SWITCH - REAR
The optional rear heater-A/C unit blower motor is controlled by a four position rotary-type blower motor switch, mounted in the accessory switch plate located to the right of the heater-A/C control on the instrument panel. The switch allows the selection of one of three blower motor speeds and an OFF position.
The rear blower motor switch directs the blower motor ground path to the blower motor resistor, or provides a ground directly to the high speed blower motor relay, as required to achieve the selected blower motor speed.
The rear blower motor switch cannot be repaired and, if faulty or damaged, it must be replaced. The rear blower motor switch knob is serviced separately. The rear blower motor switch also has a replaceable incandescent-type illumination lamp bulb.
MODE DOOR ACTUATORS
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.
BLEND DOOR ACTUATOR
The blend-air door on heater-only and heater-A/C models is connected with a short mechanical link to an electronic blend-air door actuator motor. The blend-air door motor controls the positioning of the blend-air door in the heater-A/C housing. The blend- air door motor is mounted to the top of the right end of the distribution duct under the instrument panel in the passenger compartment.
A mechanical link is attached to the end of the blend-air door motor lever in the passenger compartment and passes through a bellows-type boot and a small hole in the dash panel to the engine compartment. In the engine compartment, the link is attached to the end of the blend air door lever on the top cover of the heater-A/C housing.
The blend-air door motor is controlled by a potentiometer that is integral to the heater-only or heater- A/C control. The rotary-type temperature control knob positions the potentiometer, and the potentiometer controls the voltage to the blend-air door motor. The blend-air door motor moves the blend-air door based upon the voltage level of the signal received from the potentiometer.
The blend-air door motor is accessible for service through the instrument panel glove box opening. The blend-air door motor cannot be repaired and, if faulty or damaged, it must be replaced. The mechanical link and boot are available for service replacement.
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.