An iced-up evaporator is a common service call for any service technician working in this industry. Generally, determining this is the cause of the system problem is rather easy. But what caused the evaporator to ice up may not always be obvious.
Troubleshooting an iced evaporator should begin with a visual inspection of the coil and its icing pattern. This may not always be easy, as some cabinets or enclosures can make it hard to inspect. In other cases, the evaporator is mounted high up in the case, making it difficult to see. But, a technician should take the extra time to inspect the coil, as it will help him or her determine the true cause of the problem.
Generally, an iced evaporator is caused by one of three things:
• A low refrigerant charge;
• Poor or no airflow across the coil; or
• A defrosting issue.
The icing pattern of a system with a low refrigerant charge will generally not be uniform. Normally, the inlet of the coil will be heavy with ice, and, depending on the level of the lost refrigerant and how long it has been left in this condition, the ice will start to thin along the length of the coil. In many cases, there will just be a ball of ice on the inlet of the evaporator only.
A completely and uniformly iced evaporator is normally the result of either inadequate defrosting or little or no airflow across the coil. To determine which of these two caused the issue, first completely de-ice the evaporator. When de-icing an evaporator coil, be sure to 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 way to defrost a coil is with 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.
Once the coil is de-iced, run the system and inspect the evaporator fan(s) to make sure they are running in the proper direction and at full speed. Then, measure the superheat value of the refrigerant leaving the evaporator. If the superheat value is too low, it is generally caused by low airflow across the coil. It could also be the result of a defective metering device.
Inspect the airflow pattern of the case and make sure nothing is restricting the air across its coil. If the superheat value is acceptable, check the defrost controls and their operation, as this may likely be the cause of the problem.
Visually inspecting the condition of the evaporator coil is a valuable step in troubleshooting icing issues. It may take a little extra effort at times, but the investment of time and energy will allow a tech to more accurately determine the true cause of the issue.
Publication date: 7/4/2016