VDOT A/C Refrigerant System

VDOT A/C Refrigerant System:

The basic operation of the Variable Displacement Orifice Tube (VDOT) refrigeration system is the same as for conventional A/C systems. The VDOT refrigeration system utilizes a variable displacement compressor which contains seven cylinders; a V7 compressor that can maintain the automotive air conditioning demand under all conditions without cycling the compressor.

The basic compressor mechanism is a variable angle wobble-plate with axially oriented cylinders. The control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor which senses 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 control 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 control 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 seven 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.

The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing. The rotation acts as an oil separator, which removes some of the oil from the crankcase-suction bleed, rerouting it to the crankcase where it can lubricate the compressor mechanism.

The compressor, depending upon engine usage, is cut-off under certain conditions, such as wide-open throttle, low idle speed, low ambient air temperature, high power steering loads and high engine oil or engine coolant temperatures. The V7 compressor has a mechanical destroker that will destroke during engine speeds of 3000-3800 RPM.

When the air conditioning system is turned OFF, the refrigerant in the system will flow from the high pressure side of the evaporator tube orifice to the low pressure side until the pressure is equalized. When the engine is turned to OFF without first turning OFF the A/C system, this may be detected as a sound of liquid flowing (a hissing sound) for 30-60 seconds and is a normal condition.