Carrier Supra 950MT Operation & Service Manual

Also see for SUPRA 950Mt: Operation and service manual Operator's manual

2-13 62-11863Figure 2.10 Cylinder Head - Unloaded1. Solenoid valve2. Valve stem3. Gas bypass port4. Spring guide5. Spring6. Piston7. Piston bypass valve8. Bleed orifice9. Strainer10. Suction manifold11. Cylinder discharge valve12. Valve plate13. Cylinder suction plate14. Discharge piston check valve assembly15. Discharge manifold- - - - -b. Compressor ManifoldThe Supra 950MT unit compressor is fitted with one electric unloader valve. The capacity-controlled cylinder iseasily 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 verylittle power. A description of unloader operation is provided in the following steps.Unloaded OperationRefer 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 thanthe 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 valveback, 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 thecompressor 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.12 3456789101112131415