Electrical and Vacuum Diagnostics

HVAC System Air Flow - Typical:

System:

GENERAL DESCRIPTION
Passenger compartment comfort is maintained by the mix of cooled ambient air and heated air as controlled by the temperature lever on the instrument panel.

The A/C system uses the V-5 Variable Displacement compressor along with a Thermal Expansion Valve (TXV) as a flow control device.

Electrical and vacuum system related diagnosis are located under Electronic Control Diagnostics. Testing and Inspection

Engine Control Module (ECM) controlled components are diagnosed in Powertrain Management. Testing and Inspection

VARIABLE DISPLACEMENT COMPRESSOR - THERMAL EXPANSION VALVE REFRIGERANT SYSTEM
The Variable Displacement Thermal Expansion Valve Refrigerant system employs the constant run V-5 compressor. The V-5 is a variable displacement compressor that can match the automotive air conditioning demand under all conditions without cycling. The basic compressor mechanism is a variable angle wobble-plate with 5 axially oriented cylinders. The center of control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor that senses compressor suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-suction pressure differential. When the A/C capacity demand is high, the suction pressure will be above the control point; the valve will maintain a bleed from crankcase to suction; no crankcase-suction pressure differential; and the compressor will have maximum displacement. When the A/C capacity demand is lower and the suction pressure reaches the control point, the valve will bleed discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. The angle of the wobble-plate is controlled by a force balance on the 5 pistons. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons resulting in a movement about the wobble-plate pivot pin that reduces the plate angle.