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HomeRepair HelpCentral A/C RepairCentral air conditioner coil icing up Repair
Central air conditioner coil icing up
If your central air conditioner coil is icing up, the evaporator coil may be frozen because airflow is restricted or refrigerant flow is incorrect. Start with the humidifier damper, which should be closed or set to summer mode so air cannot bypass the evaporator coil. Next, inspect the blower motor in the furnace or air handler. A seized motor, failed motor, or blower wheel that does not turn freely can cause an evaporator coil frozen condition. A clogged blower wheel and housing can also reduce airflow and lead to an AC coil freezing up, so clean the wheel carefully with compressed air or a soft brush. A failed run capacitor or blower capacitor may keep the blower motor from running. The thermal expansion valve, or TXV, can also cause ac icing over by misregulating refrigerant in the evaporator coil. Turn off power before inspecting components, and treat 240V wiring and capacitors as beyond basic DIY scope. TXV or refrigerant-line service requires EPA 608 certification and a licensed HVAC technician. Enter your central air conditioner's model number to find the exact replacement blower motor, blower wheel, capacitor, or other part for your system.
01 - Humidifier Damper is Open
An 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.
Highly Likely
02 - Central Air Conditioner Blower Motor
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.
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Highly Likely
03 - Central Air Conditioner Blower Wheel and Housing
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.
Common
04 - Central Air Conditioner Run Capacitor
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.
Common
05 - Central Air Conditioner Capacitor
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.
Common
06 - Central Air Conditioner Thermal Expansion Valve
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.
Common
Frequently Asked Questions
Why is my central AC coil freezing up?
Can a dirty blower wheel cause my air conditioner to freeze up?
How do I test the blower motor or run capacitor when my AC coil is icing over?
Should I replace the TXV or add refrigerant when my evaporator coil is frozen?
How do I find the correct replacement part for my icing-up central air conditioner?
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