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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A technician is troubleshooting a commercial freezer maintaining a higher-than-setpoint temperature. The refrigerant sight glass is showing bubbles, and the discharge pressure is normal while the suction pressure is slightly low. What is the probable issue?

Bubbles in the sight glass with a slightly low suction pressure and normal discharge pressure are classic indicators of a refrigerant undercharge. This reduces

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Question: A technician is troubleshooting a commercial freezer maintaining a higher-than-setpoint temperature. The refrigerant sight glass is showing bubbles, and the discharge pressure is normal while the suction pressure is slightly low. What is the probable issue?

Answer options:

  • Restricted return air filter
  • Defective evaporator fan motor ✅ Refrigerant undercharge
  • Non-condensable gases in the system

Correct answer: Refrigerant undercharge

Explanation: Bubbles in the sight glass with a slightly low suction pressure and normal discharge pressure are classic indicators of a refrigerant undercharge. This reduces cooling capacity, leading to warmer box temperatures.

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