AC Not Cooling: How to Diagnose and Fix It
Your air conditioner running but not cooling is one of the most miserable home problems in summer. Before you call an HVAC company, there are several things to check yourself — some of them (like a clogged filter or tripped breaker) you can fix in minutes for free.
Likely Causes
- 1Clogged or dirty air filter restricting airflow
- 2Outdoor condenser unit covered in debris or overgrown vegetation
- 3Refrigerant leak (gradual cooling loss over days/weeks)
- 4Frozen evaporator coil (ice visible on the indoor unit)
- 5Faulty or incorrectly set thermostat
- 6Tripped circuit breaker for the outdoor unit
- 7Failed capacitor (outdoor unit hums but fan doesn't spin)
High urgency in extreme heat — dangerous for elderly, children, and pets. Check DIY fixes immediately; call a tech same day if they don't resolve it.
How to Fix It: Step by Step
- 1Check the air filter
A severely clogged filter can reduce airflow enough to freeze the evaporator coil and stop cooling entirely. Replace the filter if it's gray and compacted.
- 2Check the thermostat
Confirm it's set to COOL (not FAN), the temperature setpoint is below current room temperature, and the fan is set to AUTO. Replace the batteries if the display is dim.
- 3Check the circuit breaker
The outdoor condenser and indoor air handler may be on separate breakers. Check both. Reset any tripped breaker once — if it trips again immediately, stop and call a tech.
- 4Inspect the outdoor condenser unit
Clear any vegetation, debris, or mulch within 2 feet. The coils on the outside of the unit should be visible and not caked with dirt. You can gently rinse them with a hose from the inside out.
- 5Check for a frozen indoor unit
If you see ice on the copper lines or on the indoor unit, turn the system to FAN ONLY and let it thaw for 2–4 hours. If it freezes again, you likely have a refrigerant or airflow issue requiring a tech.
- 6Call an HVAC technician
If none of the above resolves the issue, call for service. The most common pro-required fixes are refrigerant recharge (low refrigerant) and capacitor replacement — the latter is about $150–$300.
Materials & Tools Needed
Warning Signs It's Getting Worse
- ⚠Ice forming on refrigerant lines or indoor unit
- ⚠Unusual grinding or screeching from the outdoor unit
- ⚠Outdoor fan not spinning when compressor is running
- ⚠Water dripping from indoor unit onto the floor
When to Call a Professional
Call an HVAC technician if the filter is clean, the condenser is clear, and the system still isn't cooling — refrigerant handling requires a licensed technician with EPA certification.
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