Capacity control for compression expansion refrigeration systems

Claim 1

A capacity control for a compression refrigeration system having a compressor connected in a refrigerant circuit with a condensing coil to an expansion device and an evaporator coil comprising, a suction modulation valve in the suction line between said evaporator coil and said compressor, servo means to be activated to variably close said modulation valve to change the capacity of the system, a hot gas injection line connected between said compressor and said evaporator to bypass said condenser and inject hot refrigerant gas directly from said compressor into said evaporator to reduce the capacity of the system, a normally closed hot gas valve in said hot gas line to be opened when the capacity of the system is to be reduced from maximum capacity, and thermostatic control means to inactivate the servo control of said modulation valve in the open position and to cause said hot gas valve to be in the closed position when maximum capacity is desired and the controlled refrigerated load temperature is above a predetermined amount above the desired controlled load temperature, said thermostatic control means being responsive to open said hot gas valve and activate the servo means for said modulation valve when the temperature falls below the predetermined amount above the desired load temperature whereby the capacity of the refrigeration system is directly reduced a predetermined amount by the opening of the hot gas valve and is gradually reduced beyond the predetermined amount by the operation of said modulation valve to obtain the desired load temperature.