Universal diagnostic library
Air-conditioner troubleshooting
Verify thermostat demand, indoor airflow and outdoor-unit operation first.
An air conditioner that blows warm air or does not start deserves four checks first: the thermostat set to cool and below room temperature, the breaker and the outdoor disconnect, a clean air filter and a clear outdoor unit. A frozen indoor coil is usually restricted airflow, so turn the cooling off, run the fan to thaw it and change the filter. Refrigerant leaks and electrical faults are for a licensed technician.
Air conditioner problems: what to check before calling
A central air conditioner cools by moving heat out through the indoor coil and the outdoor unit, so the commonest reasons for poor cooling are restricted airflow and a dirty or frozen coil. Replace the filter, make sure the vents and returns are open, and check that the thermostat is set to cool below the room temperature. A frozen indoor coil shows as ice on the pipe or poor airflow; turn the cooling off, run the fan to thaw it and find out why it froze before turning it back on.
The outdoor unit needs clear space around it, free of leaves and plants. A tripped breaker can be reset once. Water around the indoor unit is usually a clogged condensate drain. Low refrigerant, a failed capacitor or compressor problems are for a licensed technician, since they involve live electrical parts and refrigerant.
Why is my air conditioner running but blowing warm air?
A dirty filter, a frozen coil, a dirty outdoor unit or low refrigerant are the usual reasons. Check the filter and the coil first.