An iced-up evaporator is a common service call for any technician. A visual inspection of the coil will reveal this obvious problem.
But visually inspecting the coil is not always easy. The evaporator coil is usually enclosed in some type of housing, making it hard to inspect. It can also be mounted high up, as in the case of a large walk-in cooler or freezer, making it even more difficult to inspect.
On a running system that is not cooling properly, most technicians will install their service gauges on the system and read both the suction and discharge pressures. A system with a completely iced-up coil will show lower than normal suction and discharge pressures.
Technicians could easily misdiagnose this condition as a system low on charge if they do not visually inspect the evaporator coil. If there is this misdiagnosis, and refrigerant is added to the system, they now have overcharged the system and have created an additional problem.
It is vitally important to visually inspect the evaporator coil when troubleshooting a system with lower than normal suction and discharge pressures.
Visually inspecting the condition of the evaporator coil will aid the technician in determining if the system:
Is low on its refrigerant charge;
Has poor or no airflow across the evaporator coil; or
Has a problem defrosting.
A system low on charge may show some icing on the evaporator coil, but it will normally only be at the inlet of the evaporator coil at the outlet of the metering device. The icing will normally be contained to this area as opposed to the entire coil being iced up.
A completely iced evaporator is normally the result of either inadequate defrosting or little or no airflow across the coil. The technician can determine the cause by visually inspecting the evaporator fans to make sure they are running in the proper direction and at full speed. Then the technician can inspect the airflow leading to the evaporator coil to make sure it is not blocked.
Once an evaporator has become iced up, it is important to completely de-ice the coil in order to completely repair the system. 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 ways to defrost a coil are 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, as draining the water can be an obstacle.
Visually inspecting the condition of the evaporator coil is an integral step in troubleshooting any air conditioning or refrigeration system.
Marchese is the owner of Arctic-Air Refrigeration, Pittsburgh, PA.