You can fix this
Likely cause: the outdoor unit isn't running
If the indoor fan blows but the outdoor unit is silent, nothing is cooling the air. Check its power first, then work through the AC won't turn on troubleshooter.
Why this happens
The outdoor unit holds the compressor and the fan that remove heat from your house. Lennox lists a tripped breaker or fuse first among the reasons an outdoor unit won't run, followed by the thermostat, a capacitor, the fan motor and frozen coils. Carrier advises turning the AC off if it keeps blowing warm air, because running a malfunctioning system can overheat the compressor.
How to fix it
- Set the thermostat to Off so the system stops running while you check.
- At the breaker panel, open only the hinged door, never the metal cover behind it, and look for a tripped AC breaker. Reset it once. If it trips again, leave it off and call a technician.
- Check the disconnect box mounted on the wall near the outdoor unit and make sure it is switched on.
- Set the thermostat back to Cool and listen at the outdoor unit for a few minutes.
- If it still won't start, or it hums without the fan turning, use the AC won't turn on troubleshooter for the next checks.
When to stop. If the breaker trips again after one reset, stop. Lennox says a breaker that re-trips points to an overloaded circuit, which is a job for a technician.
If this does not fix it, tell the HVAC technician
- The outdoor unit stays silent, or hums without the fan spinning, while the indoor blower runs.
- Whether a breaker tripped and whether it held after one reset.
- The brand and model from the outdoor unit's data plate.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
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