The part(s) or condition(s) listed below for the symptom Air handler coil icing up are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
The furnace or air handler air filter should be checked and replaced at least twice a year, more often in dusty/dirty environments. A clogged air filter will greatly reduce the air flow of the furnace or air handler blower, causing the evaporator coil to ice up.
If the run capacitor is defective, the blower fan motor may fail to run which could result in the evaporator coil icing up. To determine if the run capacitor has failed, test the capacitor with a multimeter. If the capacitor is unable to hold and release a charge or is bulging or leaking, replace it.
If the capacitor is defective, the blower fan motor may fail to run which could result in the evaporator coil icing up. To determine if the capacitor has failed, test the capacitor with a multimeter. If the capacitor is unable to hold and release a charge or is bulging or leaking, replace it.
Proper air flow is critical for the central air conditioner to work properly. The evaporator needs proper air flow to keep the condensing water from freezing. If the air filter or blower wheel gets clogged, ice can start forming on the evaporator coils, eventually freezing them up. It is recommended to replace the air filter at least every 6 months, or sooner depending on the conditions. Avoid covering registers with furniture, rugs, or other items that will restrict the air flow.
Over time, the blower wheel and housing can become clogged with dust and debris. This will restrict the air flow which could result in the evaporator coil icing up. You can try cleaning the blower wheel with compressed air or with a soft bristle brush. Use caution when trying to clean the blower wheel as the fins are sharp and can be easily damaged. If the blower is damaged, it will need to be replaced.
Since the furnace or air handler blower motor is the component that circulates the air through the unit to cool it, a defective blower motor could result in the evaporator coil icing up. You can use a multimeter to test the blower motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the blower motor will need to be replaced.
If the air flow is good but the evaporator coil is still freezing up, there is likely a leak in the sealed system. If the refrigerant is low, the coil will start to freeze up on one side or section. When this happens, you may also notice a loss of cooling and water leaking near the coil. If you suspect the system is low on refrigerant, have the system checked by a licensed technician.
Some air registers have adjustable louvers that allow the air flow to be restricted or shut off entirely. This would be used to cut off the air flow to a room that isn't being used, or to restrict air flow to one room so more air will flow to the other rooms. If there is low air flow, check that the louvers are fully open.
Over time, the blower wheel can become clogged with dust and debris. This will greatly affect the air flow circulating throughout the home. You can try cleaning the blower wheel with compressed air or with a soft bristle brush. Use caution when trying to clean the blower wheel as the fins are sharp and can be easily damaged. A damaged blower wheel will need to be replaced.
