What is the first step taken before initiating a hot gas defrost cycle?

The first step taken before initiating a hot gas defrost cycle is to open the defrost valve. This action is essential because it allows hot refrigerant gas, typically warmed up by compression, to flow into the evaporator coils where frost or ice has built up. The introduction of this hot gas increases the temperature of the coils, effectively melting the accumulated ice or frost.

The other potential steps, such as stopping the compressor or adjusting the temperature set point, may occur during the overall defrost process but are not prerequisites for beginning the actual cycle. Closing the expansion valve is also typically part of managing the refrigerant flow, but it is not the first action required to start the hot gas defrost. Opening the defrost valve is specifically the critical first action that enables the defrost process to begin efficiently.