Aux 2 Unit 9 Refrigerant Under/ re-charge, leaks, trouble shooting Q3 Answer

5. Describe the indications of, and the remedies for, an undercharge on a refrigeration system.(10)

Indications of an Undercharge on a Refrigeration System (5 marks)

1. Low suction (evaporator) pressure – insufficient refrigerant in the evaporator.
2. High superheat at the compressor suction – refrigerant fully evaporates before leaving evaporator.
3. Reduced cooling capacity – space temperature does not drop to required level.
4. Bubbles in the liquid sight glass – indicates insufficient liquid refrigerant supply.
5. Compressor short cycling – frequent cut-in/cut-out due to low suction pressure.
6. Evaporator coils not fully flooded – part of coil remains warm.

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Remedies for an Undercharge (5 marks)

1. Locate and repair leaks – perform leak testing with dry nitrogen and soap solution, or electronic leak detector.
2. Evacuate the system – remove air and moisture with a vacuum pump before recharging.
3. Recharge with correct refrigerant type and quantity – add refrigerant until sight glass is clear and system pressures are normal.
4. Check expansion valve operation – ensure correct refrigerant flow to evaporator.
5. Monitor system performance after charging – confirm suction/discharge pressures, temperatures, and superheat values are within design limits.