Aux 2 Unit 9 Refrigerant Under/ re-charge, leaks, trouble shooting Q1 Answer
Describe EACH of the following vapour compression refrigeration faults, outlining a possible cause for EACH: (a) undercharge;(3) (b) overcharge;(3) (c) short cycling.(4)
(a) Undercharge of Refrigerant (3 marks)
Description: Too little refrigerant in the system → insufficient cooling capacity. Evaporator may not be fully flooded, causing low suction pressure.
Symptoms: Low suction pressure, compressor overheating, possible frosting at the expansion valve, reduced cooling performance.
Possible Cause: Refrigerant leak from joints, seals, or connections; incorrect charging during maintenance.
(b) Overcharge of Refrigerant (3 marks)
Description: Too much refrigerant in the system → excessive liquid in the condenser and high head pressure.
Symptoms: High discharge pressure, high condenser temperature, risk of liquid carryover (liquid slugging) to the compressor, poor efficiency.
Possible Cause: Overfilling during charging, failure to measure refrigerant correctly.
(c) Short Cycling (4 marks)
Description: Compressor starts and stops frequently without running long enough to maintain stable cooling.
Symptoms: Fluctuating temperatures, high wear on starter equipment, reduced compressor life.
Possible Causes:
Faulty or incorrectly set thermostat/pressure switch.
Refrigerant undercharge leading to low suction pressure cut-out.
Electrical faults in control circuit.
Blocked air/refrigerant flow causing rapid temperature rise/fall.
