2-13 62-11863
Figure 2.10 Cylinder Head - Unloaded
1. Solenoid valve
2. Valve stem
3. Gas bypass port
4. Spring guide
5. Spring
6. Piston
7. Piston bypass valve
8. Bleed orifice
9. Strainer
10. Suction manifold
11. Cylinder discharge valve
12. Valve plate
13. Cylinder suction plate
14. Discharge piston check valve assembly
15. Discharge manifold
- - - - -
b. Compressor Manifold
The Supra 950MT unit compressor is fitted with one electric unloader valve. The capacity-controlled cylinder is
easily identified by the solenoid, which extends from the side of the cylinder head. When the solenoid is energized,
two cylinders are unloaded. The unloaded cylinders operate with little or no pressure differential and consume very
little power. A description of unloader operation is provided in the following steps.
Unloaded Operation
Refer to Figure 2.10. Pressure from the discharge manifold (Item 15) passes through the strainer (9) and bleed ori-
fice (8) to the back of the piston bypass valve (7). Unless bled away, this pressure tends to close the piston (6)
against the piston spring (5) pressure.
With the solenoid valve (1) energized the solenoid valve stem (2) opens the gas bypass port (3).
Refrigerant pressure is bled to the suction manifold (10) through the opened gas bypass port. A reduction in pres-
sure on the piston bypass valve takes place because the rate of bleed through the gas bypass port is greater than
the rate of bleed through the bleed orifice (8).
When the pressure behind the piston has been reduced sufficiently, the valve spring forces the piston bypass valve
back, opening the gas bypass from the discharge manifold to the suction manifold.
Discharge pressure in the discharge manifold closes the discharge piston check valve assembly (14), isolating the
compressor discharge manifold from the individual cylinder bank manifold.
The unloaded cylinder bank continues to operate fully unloaded until the solenoid valve control device is de-ener-
gized and the gas bypass port is closed.
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