Part 1 of 2

ENGINE COOLING SYSTEM REQUIREMENTS
To maintain ample temperature levels from the heating-A/C system, the cooling system must be in proper working order. Refer to Lubrication and Maintenance.

The use of a bug screen is not recommended. Any obstructions forward of the condenser can reduce the effectiveness of the air conditioning system.

SAFETY PRECAUTIONS AND WARNINGS

WARNING:
- WEAR EYE PROTECTION WHEN SERVICING THE AIR CONDITIONING REFRIGERANT SYSTEM. SERIOUS EYE INJURY CAN RESULT FROM EYE CONTACT WITH REFRIGERANT. IF EYE CONTACT IS MADE, SEEK MEDICAL ATTENTION IMMEDIATELY.
- DO NOT EXPOSE REFRIGERANT TO OPEN FLAME. POISONOUS GAS IS CREATED WHEN REFRIGERANT IS BURNED. AN ELECTRONIC TYPE LEAK DETECTOR IS RECOMMENDED. LARGE AMOUNTS OF REFRIGERANT RELEASED IN A CLOSED WORK AREA WILL DISPLACE THE OXYGEN AND CAUSE SUFFOCATION.
- THE EVAPORATION RATE OF REFRIGERANT AT AVERAGE TEMPERATURE AND ALTITUDE IS EXTREMELY HIGH. AS A RESULT, ANYTHING THAT COMES IN CONTACT WITH THE REFRIGERANT WILL FREEZE. ALWAYS PROTECT SKIN OR DELICATE OBJECTS FROM DIRECT CONTACT WITH REFRIGERANT. R-134a SERVICE EQUIPMENT OR VEHICLE A/C SYSTEM SHOULD NOT BE PRESSURE TESTED OR LEAK TESTED WITH COMPRESSED AIR. SOME MIXTURES OF AIR and R-134a HAVE BEEN SHOWN TO BE COMBUSTIBLE AT ELEVATED PRESSURES. THESE MIXTURES ARE POTENTIALLY DANGEROUS AND MAY RESULT IN FIRE OR EXPLOSION CAUSING INJURY OR PROPERTY DAMAGE.
- ANTIFREEZE IS AN ETHYLENE GLYCOL BASE COOLANT AND IS HARMFUL IF SWALLOWED OR INHALED. SEEK MEDICAL ATTENTION IMMEDIATELY IF SWALLOWED OR INHALED. DO NOT STORE IN OPEN OR UNMARKED CONTAINERS. WASH SKIN AND CLOTHING THOROUGHLY AFTER COMING IN CONTACT WITH ETHYLENE GLYCOL. KEEP OUT OF REACH OF CHILDREN AND PETS. DO NOT OPEN A COOLING SYSTEM WHEN THE ENGINE IS AT RUNNING TEMPERATURE. PERSONAL INJURY CAN RESULT.

CAUTION: The engine cooling system is designed to develop internal pressure of 97 to 123 kPa (14 to 18 psi). Allow the vehicle to cool a minimum of 15 minutes before opening the cooling system.

Fig.6 A/C Compressor Clutch Relay:

A/C COMPRESSOR CLUTCH RELAY
The A/C compressor clutch relay is a International Standards Organization (ISO) micro-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO micro-relay terminal functions are the same as a conventional ISO relay. However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay. The A/C compressor clutch relay is located in the Power Distribution Center (PDC) in the engine compartment. See the fuse and relay layout label affixed to the inside surface of the PDC cover for A/C compressor clutch relay identification and location.

The black, molded plastic case is the most visible component of the A/C compressor clutch relay Five male spade-type terminals extend from the bottom of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each terminal. The ISO terminal designations are as follows:
- 30 (Common Feed) - This terminal is connected to the movable contact point of the relay
- 85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
- 86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
- 87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
- 87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.

The factory-installed A/C compressor clutch relay cannot be adjusted or repaired. If the relay is damaged or faulty it must be replaced.

The A/C compressor clutch relay is an electromechanical switch that uses a low current input from the Powertrain Control Module (PCM) to control the high current output to the Compressor clutch electromagnetic coil. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The A/C compressor clutch relay terminals are connected to the vehicle electrical system through a receptacle in the PDC. The inputs and outputs of the A/C compressor clutch relay include:
- The common feed terminal (30) receives a battery current input from a fuse in the PDC through a fused B(+) circuit at all times.
- The coil ground terminal (85) receives a ground input from the PCM through the A/C compressor clutch relay control circuit only when the PCM electronically pulls the control circuit to ground.
- The coil battery terminal (86) receives a battery current input from a fuse in the fuse block module through a fused ignition switch output (run-start) circuit only when the ignition switch is in the ON or Start positions.
- The normally open terminal (87) provides a battery current output to the compressor clutch coil through the A/C compressor clutch relay output circuit only when the A/C compressor clutch relay coil is energized.

The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the A/C compressor clutch relay coil is de-energized.

Refer to the appropriate wiring information for complete air conditioning-heater wiring diagrams.

A/C HEATER CONTROL
Both the heater-only and heater-A/C systems use a combination of, electrical, cable, 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 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 panel is located to the right of the instrument cluster on the instrument panel. The control panel contains rotary-type knobs. There is a blower motor speed switch, mode control switch, temperature control, and airflow control.

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

Fig. 16 High Pressure Cut Out Switch Location:

A/C HIGH PRESSURE SWITCH
The high pressure cut out switch is located on the rear of the compressor. It turns OFF the compressor if the system pressure exceeds 3240 kPa (470 psi). The high pressure cut out 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 A/C low pressure switch is a single pole, single throw, pressure actuated switch that is installed in a threaded port into the suction passage of the accumulator. The switch is located on the top of the accumulator in a fitting that contains a Schrader type valve, which allows the switch to be serviced without discharging the refrigerant system. The accumulator fitting is equipped with a O-ring to seal the switch plumbing connection.

The A/C low pressure switch is a factory calibrated unit. The switch cannot be adjusted or repaired and if faulty or damaged it must be replaced.

The A/C low pressure switch monitors the pressure of the refrigerant leaving the accumulator to the compressor. The switch is connected in series electrically with the heater-A/C control blower and mode switches and the high pressure cut out switch between ground and the Powertrain Control Module (PCM). The switch contact open or close the path the ground, signaling the PCM to turn the compressor clutch ON and OFF. This regulates the refrigerant system pressure and controls evaporator temperature. Controlling the evaporator temperature prevents condensate water on the evaporator fins from freezing and obstructing air conditioning system air flow.

The A/C low pressure switch contacts are open when the suction pressure is approximately 152 kPa (22 psi) or lower. The switch contacts will close when the suction pressure rises to approximately 234 to 262 kPa (34 to 38 psi) or above. Lower temperatures, below approximately -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.

Fig.18 Blower Motor Resistor Block:

BLOWER MOTOR RESISTOR BLOCK
The blower motor resistor is located in the cowl, at the base of the windshield. There are two different resistor blocks depending on whether the vehicle is equipped with A/C or not. The blower motor resistors will get hot when in use. Do not touch resistor block if the blower motor has been running.

EVAPORATOR TEMPERATURE SENSOR - BUX
The evaporator probe can be replaced without having to remove the A/C housing from the vehicle.

The evaporator probe is located in the A/C housing and placed in the evaporator fins. The probe prevents evaporator freeze-up. This is done by cycling the compressor clutch OFF when evaporator temperature drops below the freeze point. It cycles ON when the evaporator temperature rises above the freeze point. The evaporator probe uses a thermistor probe in a capillary tube. The tube is inserted between the evaporator fins in the heater-A/C housing.

Fig.26 A/C Vacuum Line:

Fig.27 Recirculation Air Door Vacuum Actuator:

RECIRCULATION DOOR ACTUATOR
The vehicle uses vacuum to operate only the recirculation door. All other controls are cable. When vacuum is supplied to the actuator, the door moves to the Recirculation position. The actuator is spring loaded so the door moves to the Outside-air position when there is no vacuum supplied. The operation of the door can be viewed by removing the blower motor and looking up into the unit inlet.

Normally, vacuum is supplied to the actuator by placing the Circulation control knob in the Recirculation position. The Mode and the circulation control are mechanically interlocked so the circulation control cannot be placed in the RECIRC position if the mode control is at or between the mix and defrost positions. Vacuum is supplied to the actuator only when circulation control is at the RECIRC position. If the circulation control is between the outside air position and RECIRC position the system will be in outside air. If the circulation control is in the RECIRC position and the mode control is moved from the floor to the defrost positions, the circulation control will move from the RECIRC position, to the outside air position beginning at the mix position. This is to prevent window fogging.

Fig.31 Expansion Valve And Low Pressure Cut-Off Switch:

LOW TEMPERATURE SWITCH - BUX
The Low Pressure Cut Off Switch monitors the refrigerant gas pressure on the suction side of the system. The low pressure cut off switch is located on the expansion valve. The low pressure cut off switch turns OFF voltage to the compressor clutch coil when refrigerant gas pressure drops to levels that could damage the compressor. The low pressure cut out switch is a sealed factory calibrated unit. It must be replaced if defective.

DISTRIBUTION
System Airflow
The system pulls outside (ambient) air through the cowl opening at the base of the windshield. Then it goes into the plenum chamber above the heater-A/C housing. On air conditioned vehicles, the air passes through the evaporator. Air flow can be directed either through or around the heater core. This is done by adjusting the blend-air door with the TEMP control on the instrument panel. The air flow can then be directed from the panel, floor and defrost outlets in various combinations using the mode selector. There are 17 different mode selections possible. Air flow velocity can be adjusted with the blower speed selector switch on the instrument panel.

On A/C equipped vehicles the ambient air intake can be controlled by opening and closing the recirculating air door. When placed in RECIRC, air that is inside vehicle is removed continuously and recirculated through unit housing. Ambient air cannot be controlled on vehicles without A/C. The system uses outside air at all times.

The air conditioning compressor can be engaged by turning the fan switch counterclockwise from the OFF position. It can also be engaged by placing the mode control in the mix to defrost positions. This will remove heat and humidity from the air before it is directed through or around the heater core.

Fig.1 Common Blend - Air HVAC (Heating, Ventilation, Air Conditioning) System - Typical:

Heater And Air Conditioning
All vehicles are equipped with a common heater A/C housing assembly. The system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted under the instrument panel. On heater-only systems, the evaporator coil is omitted from the housing and replaced with an air restrictor plate.

Outside air enters the vehicle through the cowl top opening at the base of the windshield, and passes through a plenum chamber to the heater-A/C system blower housing. Air flow velocity can then be adjusted with the blower motor speed selector switch on the heater-A/C control panel. 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 are 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 fresh 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.

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. A temperature control knob on the heater-A/C control panel determines the discharge air temperature by moving a cable, which operates the blend-air door. This allows an almost immediate manual control of the output air temperature of the system.

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. The mode control switch uses a cable to control the mode door, while the recirculation air door is operated by a vacuum actuator motor.

On air conditioned vehicles, the outside air intake can be shut off by selecting the recirculation mode (Recirc) with the mode control knob. This will operate a vacuum actuated recirculating air door that closes off the outside fresh air intake and recirculates the air that is already inside the vehicle.

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 an evaporator probe to maintain minimum evaporator temperature and prevent evaporator freezing, and cycles the compressor clutch.

AIR OUTLETS
The demisters direct air from the unit housing through the outlets located on the top corners of the instrument panel. The demisters operate when the mode selector is anywhere between floor and defrost settings. Some air may be noticeable from the demister outlets when the mode selector is in the bi-level to floor positions.

BLOWER MOTOR
Blower Motor Wheel
The blower motor wheel is only serviced with the blower motor The wheel and the motor are balanced as an assembly. If the blower motor wheel requires replacement, the blower motor must also be replaced. Refer to blower motor for replacement procedure.

The blower motor will only operate when the ignition switch is in the ON position, and the blower control switch is in any position except OFF. The blower motor circuit is protected by a fuse in the instrument panel fuse block. The blower motor speed is controlled by regulating the battery feed through the blower control switch and the blower motor resistor. The blower motor and wheel are used to control the velocity of air moving through the heater-only or heater-A/C unit housing. The blower motor controls the velocity of the air flowing through the heater-A/C housing by spinning the blower wheel within the housing at the selected speed.