Refrigeration System Description

VDOT Refrigerant System:

CAUTION: Avoid breathing the A/C Refrigerant 134a (R-134a) and the lubricant vapor or the mist. Exposure may irritate the eyes, nose, and throat. Work in a well ventilated area. In order to remove R-134a from the A/C system, use service equipment that is certified to meet the requirements of SAE J 2210 (R-134a recycling equipment). If an accidental system discharge occurs, ventilate the work area before continuing service. Additional health and satisfy information may be obtained from the refrigerant and lubricant manufacturers.

The Variable Displacement Orifice Tube (VDOT) system is comprised of the following components:
^ A variable displacement compressor
^ A fixed expansion tube (7)

This system matches the air conditioning demands under all modes without cycling. The basic compressor mechanism is a variable angle wobble-plate with 5 cylinders. The 5 cylinders are oriented around a common axis. The center of control of the compressor displacement is the control valve. The control valve is actuated by a bellows. The control valve is located in the rear head of the compressor (16) that senses compressor suction pressure. The crankcase-suction pressure differential controls the following conditions:
^ 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 performs the following functions:
^ Maintains a bleed discharge gas into the crankcase.
^ Closes 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. The force on the pistons produces a movement about the wobble-plate pivot pin that reduces the plate angle.