Variable Displacement Orifice Tube (VDOT)

IMPORTANT: Before any work is performed on the air conditioning system, review precautions on handling Refrigerant 134a (R-134a) along with the discharging, recovery and recycling procedures.

The Variable Displacement Orifice Tube (VDOT) 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 the 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.

When the engine is turned OFF with the A/C system operating, the refrigerant in the system will flow from the high pressure side of the expansion tube (orifice) to the low pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing (hissing) for 30 to 60 seconds and is a normal condition.

The vehicle uses a PCM controlled compressor. Refer to VDOT A/C System Diagnosis, HVAC Compressor Clutch Does Not Engage or A/C Idle Circuit Diagnosis Engine Controls for diagnosis.