Heating and Air Conditioning: Description and Operation

System = R134a with Thermostatic Expansion Valve

INTRODUCTION
Both the heater and 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. When the vehicle has only a heater system, the evaporator is omitted.

Compressor - High Pressure Relief Value:

The term Fixed Displacement Compressor will be used to describe the type of A/C system used.

SYSTEM OPERATION
Engine Cooling System Requirements
To maintain adequate 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, and engine cooling systems.

Handling Tubing And Fittings
Kinks in the refrigerant tubing or sharp bends in the refrigerant hose lines will greatly reduce the capacity of the entire system. High pressures are produced in the system when it is operating. Extreme care must be exercised to make sure that all connections are pressure tight. Dirt and moisture can enter the system when it is opened for repair or replacement of lines or components. The refrigerant oil will absorb moisture readily out of the air. This moisture will convert into acids within a closed system.

CAUTION:
- The system must be completely empty before opening any fitting or connection in the refrigeration system. Open fittings with caution even after the system has been emptied. If any pressure is noticed as a fitting is loosened, retighten fitting and evacuate the system again.
- A good rule for the flexible hose lines is to keep the radius of all bends at least 10 times the diameter of the hose. Sharper bends will reduce the flow of refrigerant. The flexible hose lines should be routed so they are at least 3 inches (80 mm) from the exhaust manifold. Inspect all flexible hose lines to make sure they are in good condition and properly routed.
- The use of correct wrenches when making connections is very important. Improper wrenches or improper use of wrenches can damage the fittings.
- The internal parts of the A/C system will remain stable as long as moisture-free refrigerant and refrigerant oil is used. Abnormal amounts of dirt, moisture or air can upset the chemical stability. This may cause operational troubles or even serious damage if present in more than very small quantities.
- When opening a refrigeration system, have everything you will need to repair the system ready. This will minimize the amount of time the system must be opened. Cap or plug all lines and fittings as soon as they are opened. This will help prevent the entrance of dirt and moisture. All new lines and components should be capped or sealed until they are ready to be used.
- All tools, including the refrigerant dispensing manifold, the manifold gauge set, and test hoses should be kept clean and dry.

System Airflow
The system pulls outside (ambient) air through the air inlet in the hood. It then goes into the plenum chamber above the Heater-A/C housing where the air passes through the evaporator. The air flow can then be directed to the FLOOR or DEFROST outlets, or both vent modes can be selected. Air flow velocity can be adjusted with the blower speed selector switch on the instrument panel. The Heater-A/C system uses fresh air in all modes except Max A/C where a mixture of fresh air and recirculated air is used. When the system is in the OFF position, some air will still flow through the system (while the vehicle is in forward motion).

System Oil Level
It is important to have the correct amount of oil in the A/C system to ensure proper lubrication of the compressor. Too little oil Will result in damage to the compressor. Too much oil will reduce the cooling capacity of the system and consequently result in higher discharge air temperatures.

NOTE: The oil used in the compressor is ND8 PAG R-134a refrigerant oil. Only refrigerant oil of the same type should be used to service the system. Do not use any other oil. The oil container should be kept tightly capped until it is ready for use. Tightly cap afterwards to prevent contamination from dirt and moisture. Refrigerant oil will quickly absorb any moisture it comes in contact with. Special effort must be used to keep all R-134a system components moisture-free. Moisture in the oil is very difficult to remove and will cause a reliability problem with the compressor.

It will not be necessary to check oil level in the compressor or to add oil unless there has been an oil loss. Oil loss at a leak point will be evident by the presence of a wet, shiny surface around the leak.