Gas Flow and Defrosting Time

Hot gas defrost is typical for many commercial and industrial refrigeration applications. It requires that the compressor be energized during the defrost cycle. The hot gas is a function of compressor discharge gas being diverted from the condenser to the evaporator. Since a refrigerator is simple in design a minimum number of flow control components are used.

The hot gas is injected down stream of the expansion device when a solenoid valve opens. The flow of hot gas will flow through the evaporator and in to a suction accumulator. This is required to vaporize condensed liquid refrigerant to enhance compressor lubrication and prevent oil migration from the compressor crankcase.

Termination of the defrost cycle is usually time or a defrost termination switch mounted on the evaporator. I have never seen a hot gas defrosting refrigerator in the US. Most refrigerators are critically charged. This requires that the refrigerant charge be weighed. The required charge weight is on the data plate.

Commercial and industrial defrost applications use a counterflow method with pressure regulation. A different method significantly more complex.