An iced evaporator is a common problem encountered by technicians servicing medium-temperature refrigeration systems. A visual inspection of the coil will show this obvious problem. Most technicians will install their low-side service gauge, find the running pressure to be lower than normal, and conclude the system has a low refrigerant charge.
However, an iced evaporator can be caused by a totally different system issue. Before adding refrigerant or wasting time looking for a leak, a technician should further examine the coil and better investigate the cause of the icing. Adding unnecessary refrigerant will not fix the problem, but it may cause an additional problem and make troubleshooting the original cause more difficult.
It is true a system with low refrigerant will have some ice developed on its coil, but normally it will be heavy only at the inlet of the evaporator coil, just at the outlet of the metering device. Depending on how long the system had been left operational, the icing pattern could grow across the coil, but the pattern of ice will typically be uneven with more icing at the inlet of the coil and less icing as it travels across the coil. A completely iced evaporator is normally the result of a totally different system problem. Either there is a defrosting issue or little or no airflow across the coil. So, before deciding the cause of the icing too quickly, look closer at the coil, and see how the ice is developing.
Once the coil has been better examined, it is best to completely de-ice it and further investigate the problem. When de-icing an evaporator coil, do not use any devices that could rupture any refrigerant lines in or around the evaporator. Never use an ice pick or any other sharp instrument to de-ice the coil. The most efficient method is to use a heat gun or to initiate a defrost cycle, if possible. Using water is also an excellent method; however, this may not always be practical if draining the water is an obstacle.
With a completely defrosted evaporator, a system with a low refrigerant charge will typically have both a lower-than-normal suction and discharge pressure along with a high evaporator superheat value. A system with a defrosting issue will seem to be operating normally until the system fails to defrost regularly. A system with an airflow issue will have a lower-than-normal suction pressure along with a lower-than-normal evaporator superheat value.
By not jumping to an early diagnosis and better inspecting the condition of the evaporator coil and the system, a technician can more accurately analyze a system and avoid making a costly mistake. As with many service problems encountered by technicians, patience is a virtue and should be practiced regularly; without it, a technician’s job can be very frustrating.
Publication date: 9/4/2017
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