Heating and Air Conditioning: Description and Operation

INTRODUCTION
System = R134a w/expansion valve
Both the heater and the heater/air conditioning systems share many of the same functioning components. This deals 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.

Heater Only Unit Housing:

The unit housing is divided into two sides. The left side is called the air distribution module. The air distribution module is the same on vehicles with or without air conditioning. On the right side there is either a blower module (non-A/C vehicles) or all evaporator/blower module (vehicles with A/C). The blower module is unique to heater only systems.

The air distribution module contains the heater core and doors used to control air flow. The vehicle uses the same air distribution module on all models (with or without air conditioning).

A/C Unit Housing:

The air conditioning evaporator is located in the evaporator/blower module.

To service the heater core, evaporator and/or any of the air doors the unit housing must be removed from the vehicle.

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.

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 every thing 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 cowl opening at the base of the windshield. Then it goes into the plenum chamber above the unit 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 defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core.