Heater, Ventilation, and Air Conditioning System Operation
Notice: The refrigeration system on this vehicle uses R-134a which is not compatible with refrigerant R-12. Before servicing the system always make sure the proper servicing equipment is used or the system could become severely damaged. Always refer to the service text and manufacturer instructions included with the service equipment before proceeding.
The A/C system provides the following features:
| • | Cooled or dehumidified air for the comfort of the occupants |
| • | Power ventilation |
| • | Windshield defrosting |
| • | Side window defrosting |
During most operating conditions, outside air enters the vehicle in the following manners:
| • | The blower motor pulls in outside air through the heater and air conditioning blower case. |
| • | The forward movement of the vehicle forces in outside air. |
Air flows along the following path within the evaporator module:
- Through the evaporator core
- Through the heater core
- Into the passenger compartment
The flow of air through the heater core is determined by the positions of the right and left temperature valves.
If the ambient temperature is above 7° C (45° F), the refrigeration system will chill the evaporator to almost freezing. This action permits operation of the air conditioning or defroster functions.
As the air passes through the evaporator, the air temperature drops. Air moisture condenses on the evaporator core fins. A gravity feed through a drain hole removes the moisture from the vehicle. This action dehumidifies the air.
From the evaporator, some or all of the air may pass through the heater core. If the system is in the heating mode, the engine coolant warms the air.
If the user selects the A/C RECIRC mode, most of the air that enters the blower motor is from the passenger compartment. The air from the passenger compartment is usually cooler than the outside air. The other modes use only outside air.
VDOT A/C System
The Variable Displacement Orifice Tube (VDOT) refrigeration system has a V5 compressor. The V5 compressor can match the automotive air conditioning demand under any conditions without cycling.
The basic compressor mechanism is a variable angle wobble-plate with five axially oriented cylinders.
A bellows actuated control valve controls the compressor displacement. This control valve is located in the rear head of the compressor that senses the suction pressure of the compressor.
The crankcase suction pressure differential controls the following features:
| • | The wobble-plate angle |
| • | The compressor displacement |
The following actions occur when the A/C capacity demand is high:
| • | The suction pressure is above the control point. |
| • | The valve maintains a bleed from the crankcase to the suction. |
| • | No crankcase-suction pressure differential exists. |
| • | The compressor has maximum displacement. |
The following actions occur when the A/C capacity demand is lower and the suction pressure reaches the control point:
| • | The valve bleeds discharge gas into the crankcase. |
| • | The valve closes off a passage from the crankcase to the suction plenum. |
A force balance on the five pistons controls the angle of the wobble plate. A slight increase of the crankcase-suction pressure differential changes the total force on the pistons. This change affects the movement around the wobble-plate pivot pin and reduces the angle of the wobble plate.
The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate. This routing permits lubrication of the wobble-plate bearing. The rotation acts as an oil separator. Some of the oil is removed from the crankcase-suction bleed and rerouted to the crankcase. The rerouted oil can lubricate the compressor mechanism.
Depending upon engine usage, the compressor is cut off when the following conditions exist:
| • | Wide-open throttle |
| • | Low idle speed |
| • | Low air temperature |
| • | High power steering loads |
The refrigerant in the system flows from the high pressure side to the low pressure side of the expansion (orifice) tube when the following conditions exist:
| • | The engine is turned off. |
| • | The A/C system is operating. |
The refrigerant continues to flow until the pressure is equalized. This action may cause a faint sound of liquid flowing (hissing) for 30 to 60 seconds. The sound is a normal condition.
