The part(s) or condition(s) listed below for the symptom Central air conditioner 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.
Central Air Conditioner Not Cooling? Central Air Conditioner Troubleshooting
Central Air Conditioner Noisy? Central Air Conditioner Troubleshooting
Central Air Conditioner Fan Motor Not Running? Central Air Conditioner Troubleshooting
Central Air Conditioner Not Running? Central Air Conditioner TroubleshootingAn open humidifier damper will let air bypass the evaporator coil. This loss of air flow can cause the evaporator coil to freeze up. If you have a humidifier on your furnace or air handler, confirm the humidifer damper is in the "summer mode" or closed position.
Since the furnace or air handler blower motor is the component that circulates the air through 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.
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.
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.
A thermal expansion valve, commonly referred to as a TXV, regulates the amount of refrigerant in the evaporator coil to help maintain an optimal working temperature.
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. If the blower is damaged it will need to be replaced.
The evaporator in a central air conditioning system is located either in the furnace or air handler. Refrigerant in the system is pumped through the evaporator and absorbs heat from the circulated air passing through it from the blower. Because of the damp environment, corrosion can start to deteriorate the welds on the aluminum or copper coils. When this happens, the refrigerant can leak out of the system and the evaporator coil 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 it should be 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.
Located in a housing, the blower wheel may be directly attached to a motor or driven by a belt which spins the blower wheel to create air flow. If the blower fins are clogged or damaged, the blower wheel may not move enough air or may vibrate and cause unwanted noise. A damaged blower wheel will need to be replaced.
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.
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.
A filter drier helps to keep the refrigerant used in the condensing unit's sealed system clean and it also helps to remove moisture from the system. Although not usually the cause of a sealed system failure, the filter drier should be replaced any time the sealed system is compromised, such as when a compressor or evaporator is replaced, or when a refrigerant leak needs to be repaired.
Most central air condensing units will have a service valve on both the high side and low side ports. The service valve is used to check the refrigerant charge and to isolate the refrigerant from the evaporator coil when servicing the system. If the valve is not shutting off all the way or is leaking externally, it will need to be replaced.
