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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A refrigeration system utilizing a fixed orifice (capillary tube) expansion device is exhibiting a 'starved' evaporator and very low suction pressure. Which of the following is the most probable cause?

When moisture is present in the system, it can freeze at the point of pressure drop in the capillary tube, effectively blocking refrigerant flow. This leads to

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Question: A refrigeration system utilizing a fixed orifice (capillary tube) expansion device is exhibiting a 'starved' evaporator and very low suction pressure. Which of the following is the most probable cause?

Answer options:

  • Overcharged refrigerant system
  • Dirty condenser coil
  • Insufficient airflow over the evaporator coil ✅ Moisture freezing in the capillary tube

Correct answer: Moisture freezing in the capillary tube

Explanation: When moisture is present in the system, it can freeze at the point of pressure drop in the capillary tube, effectively blocking refrigerant flow. This leads to a starved evaporator and very low suction pressure, often intermittent as the ice thaws and refreezes.

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