My Outside AC Unit Is Not Running

If your indoor air handler is running but the outdoor condenser unit is not, the cause could be a tripped breaker, a failed capacitor, a faulty contactor, or a thermostat issue. Some checks are safe for a homeowner; electrical components inside the unit should only be serviced by an HVAC technician.

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What to Do Right Now

The indoor AC unit is running but the outdoor condenser is silent, the fan is not spinning, or the unit makes a humming sound but does not start.

Check the thermostat — make sure it is set to "cool" and the temperature is below the current room temperature
Check the electrical panel for a tripped breaker labeled AC, condenser, or outdoor unit — if tripped, flip it fully off then back on once
Check whether the indoor air handler is running (if the indoor unit is also off, the issue may be thermostat or power related)
Make sure the outdoor unit is not buried in debris, mulch, or overgrown vegetation

What Not to Do

✗Do not open the outdoor unit's electrical panel or touch capacitors, contactors, or wiring — these components carry high voltage and can hold a charge even when power is off
✗Do not attempt to manually spin the fan blade with a stick or tool — if the capacitor is failed, the motor can start unexpectedly
✗Do not reset a breaker that trips immediately again — that indicates a short or component failure

When to Call a Professional

Call an HVAC contractor if the breaker is not tripped, the thermostat is set correctly, and the outdoor unit still will not start. A humming sound with no fan movement often indicates a failed capacitor or contactor — both require a technician. If the breaker trips repeatedly when the AC tries to start, do not keep resetting it.

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FAQ

My Outside AC Unit Is Not Running — Questions

The indoor air handler and outdoor condenser run on separate circuits. If the outdoor unit's breaker has tripped, its capacitor has failed, or the contactor is stuck, the indoor unit will run but no cooling will happen. An HVAC technician can safely diagnose which component has failed.