AC/Refrigerator Paper 2 WASSCE (SC), 2016

Question 1

State the function of the following accessories of a refrigeration system: overload, high pressure cut out switches, low pressure cut out switches, anti-freeze, thermostats.

Observation

            The expected responses are:
                       
(a)        FUNCTION OF THE FOLLOWING ACCESSORIES OF A                                                          REFRIGERATION SYSTEM OVERLOAD

                        -           This is a device either temperature, pressure or current operated which will stop operation of unit if dangerous condition arise.

                        -           It is used to protect the compressor from overheating

  1. HIGH PRESSURE CUT OUT SWITCHES:

                        -           This is  an electrical control switch operated by the high side    pressure which automatically opens electrical circuit if too high pressure is reached.

                        -           It is used to stop the system when the pressure exceeds safety limit.

  1. LOW PRESSURE CUT OUT SWITCHES

      -           This is a device used to keep low side evaporating pressure from                                                     dropping below certain pressure.

      -           It is used to stop the system when evaporation or suction pressure                                                   becomes low.

      -           It also sometimes causes the compressor to produce a high vacuum at                                             high speed.

(iv)       THERMOSTAT:  
-           This is a device that is used to control the temperature of a refrigerator                                           system. 
-           This is a device which senses ambient temperature conditions and in turn                                       acts to control a circuit


(b)        TYPES OF REFRIGERATOR

  1. Single door refrigerator.
  2. Double door refrigerator
  3. Single compressor
  4. Multi compressor.

                                                                                             
(c)       Refrigerant Blend:   
-           Refrigerant blend is the liquid mixture of refrigerant which
exhibit a constant maximum and minimum boiling point  and these                                                 mixtures act as a single refrigerant.
-           It is also the combination of two or more refrigerant to produce a single                                         refrigerant.

                        Majority of the students were able to answer the questions correctly.