Description
(1) General
The variable displacement system relies an a new compressor to provide automatic response to the changing beat loads placed on the evaporator.
Study the diagram below, paying close attention to the relationship between the piston, socket plate (drive plate) and return spring.
DESCRIPTION
(2) Variable Capacity
The variable displacement compressor responds to evaporator beat loads by increasing or decreasing the cylinder displacement of the compressor
The capacity can be varied from .18 to 8.9 cubic inches by changing the piston stroke from .8236 to 1.126 inches.
DESCRIPTION
(3) Capacity Control
The length of piston stroke determines the capacity of the compressor.
A bellows valve located in the rear compressor bead changes the stroke by controlling the compressor's crankcase pressure. The bellow expands and compresses in response to low side pressure. A single pin valve is positioned by the bellows to:
1) Raise crankcase pressure, decreasing piston stroke.
2) Maintain crankcase pressure, holding piston stroke.
3) Lower crankcase pressure, increasing piston stroke.
DESCRIPTION
(4) This illustration shows the value position for lowering compressor crankcase pressure.
DESCRIPTION
(5) This illustration shows the valve position for maintaining crankcase pressure.
DESCRIPTION
(6) This illustration shows the valve position for raising crankcase pressure.
DESCRIPTION
(7) System Operation
1) Maximum Cooling Capacity/Longer Piston Stroke
When suction (low) side pressure rises above 26 psi, the bellows of the control value will start to compress; 1) decreasing the discharge
(high) side bleed into the crankcase; and 2) increasing the suction
(low) side bleed off. This will lower crankcase pressure, allowing cylinder and spring pressure to increase the angle of the driue plate prouiding a longer stroke. (see fig. Pg 6)
3) Minimum Cooling Capacity/Shorter Piston Stroke
When suction (low) side pressure drops below 26 psi, the bellows of the control valve will start to expand; 1) increasing the discharge
(high) side bleed to the crankcase: and 2) decreasing the suction
(low) side bleed off. This will raise crankcase pressure, allowing cylinder and spring pressure to decrease the drive plate angle providing a shorter stroke. (see fig. pg 8)