Short answer
If the outdoor unit hums but the fan does not spin, set the thermostat to "Off" right away to protect the compressor. Reset a tripped AC breaker once and make sure the disconnect box is on. With the power off, lift leaves and sticks off the top grille. Do not push the blades with a stick: a bad capacitor or fan motor is a job for a technician.
Safety first
Never push a stick, a screwdriver or your fingers into the fan, and never open the panels of the outdoor unit. The capacitor inside can hold a dangerous charge even with the power off. Switch the disconnect box to "Off" before you clear anything from the unit.
What to check when the outdoor AC fan stops
1Humming, but the fan is still
The outdoor unit hums and the fan on top does not turn. Running like this can overheat the compressor.
Read all the steps
- Humming, but the fan is still. The outdoor unit hums and the fan on top does not turn. Running like this can overheat the compressor.
- Thermostat to Off, right away. Stop the system while you check. Then make sure it was set to "Cool", a few degrees below the room temperature.
- Check the breaker and the disconnect. Reset a tripped AC breaker once, firmly to "Off" and then to "On". Make sure the disconnect box by the unit is on.
- Power off, clear the top grille. Switch the disconnect box to "Off". Lift leaves and sticks off the top. If something is stuck between the blades, leave it for the technician.
- No stick test, no opening the panel. Pushing the blades to start them risks a shock and a cut. A weak capacitor or a bad motor is a quick job for a technician.
- Power on: does the fan spin?. Disconnect on, thermostat to "Cool". If the fan spins, watch it a few minutes. If it hums again with the fan still, turn it off and call.
- Still not fixed? Call an HVAC contractor Especially if: the unit hums and the fan does not spin.
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Why the fan stops
- A failed capacitor, the part that helps the fan motor and the compressor start. It is the most common cause.
- A worn fan motor that overheats and stops.
- A stuck contactor, or a problem with the wiring or the controls.
- Debris jammed in the blades.
- No power to the unit: a tripped breaker or a disconnect box switched off.
What not to do
- Do not try the "stick test" you see online. The blades can start suddenly, and the parts near them carry high voltage.
- Do not open the access panel or touch the capacitor. It can shock you even with the power off.
- Do not leave the AC running with the fan stopped. The compressor can overheat and fail.
When to call an HVAC technician
- The unit hums and the fan does not spin.
- The fan spins slowly, stops after a while or only starts with a push.
- The breaker trips again after one reset.
- You smell burning near the outdoor unit.
Frequently asked questions
Why is my outside AC fan not spinning?
Most often a failed capacitor or fan motor. A tripped breaker, a disconnect box switched off, a thermostat setting or debris in the blades can also stop it.
Why is my AC humming but the fan is not spinning?
The unit has power, but the fan motor cannot start. That usually points to a bad capacitor or motor. Turn the AC off to protect the compressor and call a technician.
Can I push the AC fan with a stick to start it?
No. The blades can start suddenly and the parts near them carry high voltage. If a push starts it, the capacitor or the motor needs replacing anyway.
Can I replace an AC capacitor myself?
It is not a safe DIY job. A capacitor can hold a dangerous charge even with the power off, and the new one must match the unit. A technician can test and replace it quickly.
Is it bad to run the AC if the outside fan is not spinning?
Yes. Without the fan, the compressor overheats and can fail. Set the thermostat to "Off" until a technician checks it.