Freezer Defrost Sequence
The freezer defrost sequence is as follows:
1. Defrost is initiated, or started, according to the time setting on the defrost clock.
2. The compressor and the evaporator fan(s) stop.
3. The electric heater (or hot gas) starts warming the coil.
4. When the coil reaches a temperature high enough to have melted all the frost, a temperature sensor, called the defrost termination switch, takes the coil out of defrost and returns it to refrigeration operation.
5. The compressor starts, but the fan(s) stay off. The refrigerant now cooling the coil removes defrost heat and refreezes any remaining water droplets from defrost.
6. When the evaporator drops to approximately 25°F, the fan delay switch closes. The fans start and continue circulating air until the next defrost cycle.
Source : Commercial Refrigeration: For Air Conditioning Technicians
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