An AC that runs but blows warm air is a standard July call for HVAC technicians in the Triangle. The first few checks take ten minutes and cost nothing. If they do not fix it, the problem needs a licensed tech with refrigerant gauges.
Start at the thermostat
Confirm it is set to Cool, not Heat or Fan, and that the set point is at least three degrees below the room temperature. On a heat pump, Aux or Heat on the screen in July means someone changed the mode. If the screen is blank, replace the batteries.
Check the filter
A clogged filter starves the indoor coil of air. The coil drops below freezing, ices over and stops cooling. Pull the filter and hold it up to a light. If no light comes through, replace it, then set the system to Fan only for two to three hours to thaw the coil before switching back to Cool.
Look at the outside unit
With the thermostat calling for cooling, go outside and look at the condenser. The big fan on top should be spinning, and you should hear the compressor running under it.
- If the unit hums but the fan does not spin, a failed capacitor is the likely cause. Turn the system off at the thermostat so the compressor does not overheat, and call.
- If nothing runs at all, check the breaker in the panel and the disconnect box on the wall next to the unit. Reset a tripped breaker once.
- If the fan spins but you hear no compressor and the air inside is warm, the compressor or its start components have a problem that needs a tech.
- If everything runs and the air is only a little cool, the system is often low on refrigerant from a leak, or the coil is caked with pollen and grass clippings.
Rinse the outdoor coil
Spring in Chapel Hill leaves a film of pine pollen on every outdoor unit. Turn off the power at the disconnect box, then spray the coil fins with a garden hose on a gentle setting. Skip the pressure washer, which flattens the fins.
When to call
Call us if the breaker trips again, if ice comes back after thawing, or if the outside unit hums without the fan turning. Refrigerant work requires EPA Section 608 certification. Topping off a leaking system without fixing the leak means paying for another recharge next summer.
| Repair | Typical price |
|---|---|
| Capacitor replacement | $150 to $400 |
| Contactor replacement | $150 to $350 |
| Frozen coil diagnosis and cleaning | $150 to $450 |
| Refrigerant leak search and recharge | $400 to $1,500 |
If none of those checks fixed it, call (980) 245-1226 and we will send a licensed AC repair technician.