This one needs a licensed pro
Likely cause: a capacitor or fan motor
A hum or click with no fan, or a silent unit with power on, points to an electrical part inside the outdoor unit. That's a technician's job.
Why this happens
Lennox lists the capacitor and fan motor right after the breaker and thermostat as reasons an outdoor unit won't run, and Trane lists motor failure. These parts store and carry high voltage. Trane says servicing an AC can be dangerous and that a professional technician is trained for it.
What to do right now
- Set the thermostat to Off so the unit stops trying to start.
- Leave the outdoor unit's panels closed and don't poke anything through the fan grille.
- Switch off the disconnect box next to the outdoor unit and leave it off. Then clear loose debris from around the outside of the unit by hand, without reaching inside the fan grille.
- Check the filter while you wait. Trane lists a clogged filter as another cause, and the tech will ask.
What to tell the HVAC technician
- Whether the outdoor unit hums, clicks, or is silent when the thermostat calls for cooling.
- That the breaker and disconnect are on and the thermostat is set correctly.
- How long it has been running this way.
- The brand, model and serial from the outdoor unit's data plate.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
References (every fact above comes from one of these pages)
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