Exercises
Principal Faults
Whenever you arrive at an installation which has not been operating correctly, the very first thing to do is to speak to the client. Obtain from him as much information as possible as to why he needs your help (e.g. the ambient temperature is too high, the system is making unusual noises, the installation keeps tripping out the mains supply, another engineer has recently been working on the system, etc.). Then you must "look" at the system, "listen" to the system, and perhaps "touch" the system. This is especially important if the system is new to you. This will help you to detect any possible indications of obvious faults (e.g. general condition, traces of oil, unusual noises, odours of burning etc.). Then gauges must be fitted to the system and the identity of the refrigerant used in the system must be determined. This last information is indicated on the thermostatic line of the expansion valve, or an identification label may be present.
In the majority of instances, the system will run (poorly, but the compressor will operate). The fault will then be one of the 8 families of faults that we've been studying. Your role is to find out which, to repair it, and to make sure that there will not be any other problems in the near future.
Always think in terms of temperatures rather than pressures. Your logic will then be valid whatever refrigerant is in use in the system (R22, R134a, R404A, R407C, etc.) !
REMEMBER THAT A LARGE SUPERHEAT ALWAYS INDICATES A SERIOUS LACK OF REFRIGERANT IN THE EVAPORATOR, AND THAT POOR SUB-COOLING INDICATES EITHER A LACK OF REFRIGERANT (if the LP is low) OR A LACK OF CONDENSER CAPACITY (if the HP is high).
By referring to the general fault flow chart below, the family of faults responsible for the breakdown can be quickly identified.
EXERCISE : In the diagram below, complete all the grey boxes in order to restore the logical sequence used to diagnose the major faults that we've just studied (with an evaporator cooling air and and air-cooled condenser).
(Solution : Refrepair Manual pages 3 to 192)
