Aux 2 Unit 9 Refrigerant Under/ re-charge, leaks, trouble shooting Q9 Answer

  1. With reference to refrigeration systems, explain EACH of the following:
    (a) why air is undesirable;(3)
    (b) how air may enter;(3)
    (c) how air may be removed.(4)

(a) Why air is undesirable (3 marks)

  1. Reduces heat transfer efficiency – air is non-condensable and collects at the condenser top, reducing surface area for condensation.
  2. Raises condenser pressure – increases head pressure, leading to higher compressor power consumption and reduced efficiency.
  3. Causes corrosion and moisture issues – air can introduce moisture, leading to acid formation and potential damage to system components.

(b) How air may enter (3 marks)

  1. During charging – if poor procedures are followed when charging refrigerant into the system.
  2. Through leaks on the suction side – low-pressure side leaks may allow air to be drawn into the system while running.
  3. During maintenance – opening the system without proper purging or evacuation introduces air.

(c) How air may be removed (4 marks)

  1. By purging from the condenser – many systems have manual or automatic air purge valves at the condenser top.
  2. By evacuating the system – using a vacuum pump before recharging refrigerant ensures air and moisture are removed.
  3. By using refrigerant charging cylinders with non-condensable vents – allows trapped air to be bled off before charging.
  4. Through automatic purge units (large plants) – continuously separate and discharge air/non-condensables while retaining refrigerant.