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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A residential heat pump in heating mode is operating with low refrigerant pressures on both sides of the system, and the outdoor coil is not defrosting correctly. What is the most likely cause?

Low refrigerant charge (undercharge) in a heat pump system leads to low pressures on both the high and low sides in heating mode. This directly impacts the syst

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Question: A residential heat pump in heating mode is operating with low refrigerant pressures on both sides of the system, and the outdoor coil is not defrosting correctly. What is the most likely cause?

Answer options:

  • Reversing valve malfunction ✅ Undercharged refrigerant
  • Failed outdoor fan motor
  • Thermostat set too low

Correct answer: Undercharged refrigerant

Explanation: Low refrigerant charge (undercharge) in a heat pump system leads to low pressures on both the high and low sides in heating mode. This directly impacts the system's ability to efficiently transfer heat and can prevent proper defrosting of the outdoor coil.

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