Unloadable transport refrigeration unit control

Claim 1

The combination of: a transport refrigeration unit including prime mover means driving a multi-cylinder, unloadable compressor adapted to operate in a cooling mode, or alternatively in a heating and defrost mode, in accordance with the positioning of a three-way valve receiving hot gas discharged by said compressor, said valve having its one outlet connected to a refrigerant condenser and its other outlet connected to a hot gas line extending to a refrigerant evaporator, said hot gas line in a cooling mode having a pressure reflecting the evaporator pressure, and in a heating and defrost mode having a pressure corresponding generally to the gas discharge pressure; with a control system including: switch means responsive to the refrigerant pressure in said hot gas line; first circuit means including a first solenoid for controlling the loading of at least one of the cylinders of said compressor; second circuit means including a second solenoid for controlling the loading of the remainder of the cylinders; each of said circuit means including switch means responsive to changes in temperature of the space conditioned by said refrigeration system and independently operable to positions to unload said at least one cylinder and said remainder of cylinders in accordance with demand conditions of said space; said switch means responsive to pressure having a first position corresponding to a pressure below a predetermined value placing said second circuit means in a condition in which said second soleoid causes loading of said remainder of cylinders, and having a second position corresponding to a pressure above the predetermined value placing said second circuit means in an opposite condition in which said second solenoid causes unloading of said remainder of cylinders; whereby said system can operate in a cooling mode in loaded condition with gas discharge pressures significantly higher than said predetermined value.