Heating and Air Conditioning: Description and Operation

MANUAL A/C (HVAC)/REAR WINDOW DEFOGGER
The Prowler comes standard with manual air-conditioning. The actuators for blend-air and fresh/recirc are cable operated. The mode door is electrically activated by the BCM based on input from the HVAC control head. The BCM uses an evaporator fin probe to prevent evaporator freeze-up.

When the ignition is in the "run" position, the body control (BCM) monitors the evaporator temperature state and the status of the A/C switch. Based on this information, the BCM sends a CCD message to the powertrain control module (PCM) indicating the A/C switch status and the evaporator temperature state.

The body control module controls the mode door position by receiving different voltage levels from the HVAC control over the HVAC mode sense circuit. Included in this signal is the input for the rear window defogger. The Rear Window Defogger button is located in the center of the Mode Control knob. Press this button once to turn on the Rear Window Defogger and a second time to turn it off. A LED in the button shows that the defogger is on. The defogger turns off automatically after 10 minutes of operation. Each later activation will allow 5 minutes of operation. The timer functions for the rear window defogger are controlled by the BCM.

The heater/air conditioning systems share many of the same components. This information will deal with both systems together when component function is common, and separately when they are not.

For proper operation of the instrument panel controls, refer to the Owner's Manual provided with the vehicle.

All vehicles are equipped with a common Heater A/C unit housing assembly

SYSTEM AIRFLOW
The system draws outside air through the cowl opening at the base of the windshield. Then it goes into the plenum chamber above the Heater A/C unit housing and passes through the evaporator. At this point airflow 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 control head. After the air passes the blend air door, the air flow is then directed from the PANEL, BI-LEVEL (panel and floor), and FLOOR - DEFROST outlets. Air flow velocity can be adjusted with the blower speed selector switch on the control head.

Fig 2 HVAC Controls:

Ambient air intake can be shut off by rotating the RECIRC knob on the control head, closing the recirculating air door. This will recirculate the air that is already inside the vehicle. Rotating the MODE control knob to the Defrost/Floor or Defrost setting on the control head will engage the compressor. This will send refrigerant through the evaporator, and remove heat and humidity from the air before it goes through the heater core. The compressor can also be engaged by depressing the A/C button on the control head.

A/C PRESSURE TRANSDUCER
The A/C pressure transducer is an electro-mechanical device that functions as the refrigerant system pressure sensor. The PCM uses information from the transducer to control the radiator fans and compressor functions. The sensor is attached to a threaded valve on the liquid line -- near the compressor.

COMPRESSOR CLUTCH/PULLEY/COIL ASSEMBLY
The clutch assembly consists of a stationary electromagnetic coil, hub bearing pulley assembly, and clutch plate.

The electromagnetic coil and pulley are retained on the compressor with snap rings. The clutch plate is mounted on the compressor shaft and secured with a nut.

When the compressor is not operating, the pulley free wheels on the hub bearing which is part of the pulley. When the coil is energized the plate is magnetically engaged with the pulley and turns the compressor shaft.

COMPRESSOR
The compressor used on this vehicle is a Nippondenso 10PA17 R134a. This compressor uses an aluminum swash plate, teflon coated pistons and aluminum sleeved cylinder walls. One-way check valves are used to regulate refrigerant flow through the compressor.

CAUTION: A 10PA17 R-12 compressor looks identical to a 10PA17 R134a and will bolt up to this vehicle. It is extremely important that a R-134a compressor is identified prior to using compressor in question. Check tag located on compressor for model number.

Excessive noise that occurs when the air-conditioning is being used may be caused by:
- Loose Bolts
- Mounting Brackets
- Loose Compressor Clutch
- Excessive High Refrigerant Operating Pressure

Verify the following before compressor repair is performed:
- Compressor drive belt condition
- Proper refrigerant charge
- Thermal expansion valve (TXV) operating correctly
- Head pressure is normal

CONDENSER
The condenser is located in the air flow in front of the engine cooling radiator. The condenser is a heat exchanger that allows the high-pressure refrigerant gas being discharged by the compressor to give up its heat to the air passing over the condenser fins. When the refrigerant gas gives up its heat, it condenses. When the refrigerant leaves the condenser, it has become a high-pressure liquid refrigerant.

The volume of air flowing over the condenser fins is critical to the proper cooling performance of the air conditioning system. Therefore, it is important that there are no objects placed in front of the radiator grille openings in the front of the vehicle or foreign material on the condenser fins that might obstruct proper air flow. Also, any factory-installed air seals or shrouds must be properly reinstalled following radiator or condenser service.

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

EVAPORATOR COIL
The evaporator coil is located in the heater-A/C housing, under the instrument panel. The evaporator coil is positioned in the heater-A/C housing so that all air that enters the housing must pass over the fins of the evaporator before it is distributed through the system ducts and outlets. However, air passing over the evaporator coil fins will only be conditioned when the compressor is engaged and circulating refrigerant through the evaporator coil tubes.

Refrigerant enters the evaporator from the fixed orifice tube as a low-temperature, low-pressure liquid. As air flows over the fins of the evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas before it leaves the evaporator.

The evaporator coil cannot be repaired and, if faulty or damaged, it must be replaced.

EVAPORATOR FIN SENSOR
The evaporator fin sensor can be replaced without having to remove the unit housing from the vehicle.

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

EXPANSION VALVE
The expansion valve is located in the engine compartment on the right side of the vehicle.

The expansion valve can fail in three different positions (open, closed or restricted).

In an Open Position: this will result in a noisy compressor or no cooling. The cause can be a broken spring, broken ball or excessive moisture in the A/C system. If the spring or ball are found to be defective, replace the expansion valve. If excessive moisture is found in the A/C system, recycle the refrigerant.

In a Closed Position: There will be low suction pressure and no cooling. This may be caused by a failed power dome or excessive moisture in the A/C system. If the power dome on the expansion valve is found to be defective replace the expansion valve. If excessive moisture is found recycle the refrigerant.

A Restricted Orifice: There will be low suction pressure and no cooling. This may be caused by debris in the refrigerant system. If debris is believed to be the cause, recycle the refrigerant and replace the expansion valve and receiver/drier.

Fig 1 Filter/Drier Location:

FILTER/DRIER
The filter/drier is a receiver for reserve refrigerant. It also has a desiccant bag and a filter. This is used to absorb moisture and filter the refrigerant as it passes through the filter/drier.

The filter/drier is located forward of the coolant bottle. The A/C refrigerant must be removed from the system before removing the filter/drier. Always use a refrigerant recovery machine.

Replace the filter/drier if an A/C system is left open for an extended period of time.

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

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