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Refrigeration & Air Conditioning Mechanic Red Seal · Question

Which of the following describes the most common sequence for an electric defrost cycle in a medium-temperature walk-in cooler (-5°C evaporator temperature)?

The standard electric defrost sequence involves shutting down the compressor and fans, energizing heaters, allowing for a drain time, then activating fans after

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Question: Which of the following describes the most common sequence for an electric defrost cycle in a medium-temperature walk-in cooler (-5°C evaporator temperature)?

Answer options:

  • Compressor OFF, evaporator fan OFF, defrost heaters ON, drain pan heaters ON, fan delay, defrost termination/fan delay thermostat, compressor ON, fan ON.
  • Compressor OFF, evaporator fan ON, defrost heaters ON, fan delay, defrost termination/fan delay thermostat, compressor ON, fan ON.
  • Compressor ON, evaporator fan OFF, defrost heaters ON, drain pan heaters ON, fan delay, compressor ON, fan ON. ✅ Compressor OFF, evaporator fan OFF, defrost heaters ON, drain pan heaters ON, defrost termination/fan delay thermostat, fan delay, compressor ON, fan ON.

Correct answer: Compressor OFF, evaporator fan OFF, defrost heaters ON, drain pan heaters ON, defrost termination/fan delay thermostat, fan delay, compressor ON, fan ON.

Explanation: The standard electric defrost sequence involves shutting down the compressor and fans, energizing heaters, allowing for a drain time, then activating fans after the coil cools enough (fan delay) and the termination thermostat is satisfied, before restarting the compressor.

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