In this troubleshooting situation you are dealing with equipment that has only been in operation for two months. And during that time frame, the customer has complained that at times the box temperature is higher than it should be, but the unit then seems to recover and freeze OK until the next time some of the items inside are found to be thawing.
The details on this freezer are as follows:
• The refrigeration system was field-designed and assembled with components purchased individually, and the condensing unit is sitting on top of the cabinet.
• The defrost system is hot gas, employing a timer to initiate the defrost cycle.
When you arrive to evaluate this equipment, you find all refrigerant pressures to be normal and the box temperature is near 0°F. Satisfied that the freezing mode of the unit is operating according to specifications, your next step is to force a defrost mode.
When you do, you note that the evaporator fan motor shuts down and the hot gas solenoid operates normally. Figure 1 shows you the path of refrigerant flow during the hot gas defrost mode… from the got gas solenoid valve, directly through the evaporator, and back to the compressor.
Near the end of the defrost mode, you find that the compressor kicks off on overload, and isn’t able to re-start until after an extended delay.
Your troubleshooting question: What mistake was made during the design and construction of this system, causing the compressor to shut down?
Compare your answer with ours here.
Publication date: 11/9/2015
For information on Jim Johnson’s HVACR technician training DVDs, go to http://techtrainassoc.com/training-videos/hvacr-training-videos/.