- 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) List FOUR reasons for a refrigeration compressor to stop unexpectedly, after running for a short period.(4)
(b) Describe the faults which lead to TWO of the reasons for the stoppage, listed in part (a).(6)
- Describe the indications of, and the remedies for, an undercharge on a refrigeration system.(10)
- Explain, with the aid of a sketch, the procedure for vapour re-charging of a refrigeration plant.(10)
- State THREE different methods used to detect a refrigerant gas leak, explaining EACH method.(10)
- Describe, with the aid of a sketch, the procedure for Liquid Charging refrigeration plant stating all safety procedures and checks to be carried out. (10)
6.(a) State FOUR properties of refrigeration oil.(4)
(b) Describe the operation of an Oil Separator in a refrigeration system.(4)
(c) State reasons for the employment of an oil separator in refrigeration vapour compression units.(2)
With reference to blended refrigerants, explain EACH of the following terms, stating the refrigerant state required for charging:
(a) azeotrope;
(b) zeotrope;
(c) near-azeotrope.
- 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)
Question 6.
Many fail to understand that a refrigeration system is positively pressurised throughout and give leaks as a cause of ingress of air with no explanation of how a negative pressure can occur. Many state that air can be bled and some mention pumping down but do not explain what this means or the procedure for removing air.