Variable Displacement Orifice Tube (Vdot)

Variable Displacement Orifice Tube (VDOT):

The Variable Displacement Orifice Tube (VDOT) system consists of the following components:
^ A variable displacement compressor (1)
^ A fixed expansion tube (5)This system matches the air conditioning demands 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. The valve is located in the rear head of the compressor. The valve senses compressor suction pressure. The crankcase-suction pressure differential controls the following items:
^ The wobble-plate angle
^ The compressor displacement

When the A/C capacity demand is high, the suction pressure will be above the control point. The valve will maintain a bleed of discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. A force balance on the 5 pistons controls the angle of the wobble-plate. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons that results in a movement about the wobble-plate pivot pin. The movement reduces the plate angle.