Few things are more frustrating than an air conditioner that runs but doesn’t cool. Before you call for service, here are six common causes — some you can fix yourself in minutes.

1. Dirty or Clogged Air Filter

This is the most common cause we find — and the easiest fix. A clogged filter restricts airflow so severely that the system can’t move enough air across the evaporator coil to cool your home.

Fix: Replace the filter. If your filter looks gray and packed with debris, it’s past due. Replace every 1–3 months depending on usage and pets.

2. Frozen Evaporator Coil

If airflow is restricted (see above) or refrigerant is low, the evaporator coil can freeze solid. When frozen, the system is physically incapable of cooling your home.

Signs: Ice visible on the indoor unit, warm air from vents, water dripping when it thaws.

Fix: Turn the system to FAN ONLY for 2–4 hours to thaw the coil. If it refreezes, call a technician — you likely have a refrigerant leak.

3. Low Refrigerant (Leak)

Refrigerant isn’t “used up” — if your system is low, it’s leaking. Low refrigerant means your system can’t absorb enough heat to cool your home effectively.

Refrigerant is not something you can top off yourself. It requires an EPA 608 certified technician to diagnose, locate the leak, repair it, and recharge the system.

4. Dirty Condenser Coils (Outdoor Unit)

The outdoor unit rejects heat from your home to the outside air. If the condenser coils are caked with dirt, grass clippings, or cottonwood, that heat can’t escape — and your system struggles to cool.

Fix: Turn off the system, then rinse the coils gently with a garden hose from the inside out. Don’t use a pressure washer.

5. Failed Capacitor

Capacitors start the compressor and fan motors. A failed capacitor often causes the system to run — fans spinning, unit humming — but the compressor won’t kick in, so no cooling happens.

Signs: Outdoor unit is running but not making the normal compressor sound. Capacitors are inexpensive ($10–$30) but require a technician to safely discharge and replace.

6. Thermostat Issues

Before assuming a mechanical failure, verify your thermostat is set correctly — cooling mode, set temperature lower than current room temperature, and working batteries. If the thermostat itself is malfunctioning, it may not signal the system to cool even though everything else is fine.

When to Call a Professional

If steps 1 and the thermostat check don’t solve the problem, it’s time to call. Refrigerant handling, electrical components, and coil cleaning beyond surface level require a licensed technician.