Refrigeration unit including a hot gas defrosting system

Claim 1

A refrigeration unit operable in a cooling mode and a defrost mode, comprising: a compressor, an evaporator, a cooling circuit including a condensor, said cooling circuit for supplying hot gas discharged from said compressor to said condensor through a discharged gas line and returning said hot gas through said evaporator to said compressor, said cooling circuit comprising a liquid reservoir portion, a hot gas by-pass passage for supplying hot gas discharged from said compressor to said evaporator by-passing said condensor, a hot gas valve means for controlling opening and closing of said hot gas by-pass passage and for controlling opening and closing of said discharged gas line, a hot gas valve control means for causing, responsive to initiation of a pumping down operation, said hot gas valve means to close said hot gas by-pass passage and to open said discharged gas line and for causing, responsive to completion of said pumping down operation, said hot gas valve means to open said hot gas by-pass passage and to close said discharged gas line, a defrost circuit for supplying hot gas through said hot gas valve means to said evaporator and for returning said hot gas to said compressor, and a constant quantity refrigerant flow-out means including a first stop valve mounted in said cooling circuit downstream of said condensor, means for closing said first stop valve, responsive to completion of a said cooling mode, to enable said pumping down operation to begin such that refrigerant is sealed in said liquid reservoir portion, said constant quantity refrigerant flow-out means for supplying a predetermined constant amount of refrigerant from said liquid reservoir portion to said defrost circuit, responsive to completion of said pumping down operation, whereby a defrosting operation is performed with said predetermined constant amount of refrigerant being supplied to the defrost circuit.