Symptoms
- Air blows but isn't cold
- House temperature climbs despite the AC running
- Outdoor unit may or may not be running
Likely causes
- CommonDirty air filter restricting airflowReduced airflow over the indoor coil can prevent effective cooling.
- CommonThermostat set wrong or in the wrong modeA thermostat set to Fan Only or Heat won't cool even if the AC works fine.
- CommonDirty outdoor condenser coilA coil caked in dirt or grass clippings can't release heat efficiently, weakening cooling.
- PossibleLow refrigerant from a leakLow refrigerant reduces cooling capacity and often shows up alongside a frozen coil.
- Less commonFailing compressorThe compressor is the heart of the system, and its failure means little or no cooling.
What to do
- Confirm the thermostat is set to Cool with a target temperature below the current room temperature.
- Replace the air filter if it looks gray or clogged.
- Go outside and check the condenser unit is running; you should hear a fan and feel warm air blowing out the top.
- Turn off the system and gently hose off visible dirt or debris from the outdoor unit's fins (with power off).
- Check the indoor evaporator coil (usually behind an access panel) for ice buildup, which points to a different, related problem.
- If airflow and both units look normal but cooling is still poor, the system likely needs a refrigerant check by a technician.
Tools and parts
- Garden hose
AC air filterSearch: “central air filter size replacement”
When to call a pro
Call an HVAC technician if the filter and outdoor unit are clean but cooling stays poor; low refrigerant or a compressor issue needs professional diagnosis.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.