Outdoor AC fan not spinning? Start here.

You go outside and the condenser unit is doing nothing -- no fan, no hum, no buzz -- even though the thermostat is set to cool and the house is warm.

A completely silent unit often points toward a power or control-signal problem reaching the outdoor unit, rather than the fan itself: a thermostat that is not actually calling for cooling, or a break somewhere in the electrical or low-voltage control path. It can also overlap with a system that will not start at all.

• Confirm the thermostat is set to Cool and the temperature is set a few degrees below the current room temperature.
• Confirm the thermostat screen is on and responsive; replace the batteries if it uses them and the screen is blank.
• Note whether the outdoor unit appears to have lost power or whether a breaker is already tripped, and tell the technician what you saw.

• Do not reset a breaker when there is a burning/electrical/hot-plastic odor, smoke, sparks, unusual heat/scorching, buzzing/crackling, water near electrical equipment, or a previous repeat trip. Outside those conditions, one reset after turning the HVAC off at the thermostat is the maximum. Do not operate the outdoor disconnect.
• Do not reset a breaker repeatedly.
• Do not open or work inside the electrical panel.

• The thermostat is set to cool and responsive but the outdoor unit stays completely silent -- a technician needs to trace the power and low-voltage control path to the unit.
• A breaker is already tripped, or trips again after the system is switched off and left alone -- treat that as an electrical fault for a professional.

The outdoor unit hums or buzzes with power in it, but the top fan sits still. In some cases the fan starts turning only after it is given a push, and the air indoors is warm.

A humming unit with a stopped fan, or a fan that only starts after a push, is commonly associated with a weak or failed run capacitor or start circuit -- the part that helps the fan motor start turning. The fan motor itself can produce the same pattern. A fan that only starts when pushed is a symptom to report, not a repair.

• If the unit is humming and blowing warm air with the fan stopped, switch cooling off at the thermostat so the system is not forced to run without the fan.
• Check the thermostat setting and the indoor air filter while you wait for service.

• Do not push-start the fan with a stick, and do not spin the fan by hand -- it is a risky shortcut that can cause injury or damage, and it does not fix anything.
• Do not open, discharge, or touch the capacitor or its terminals -- a capacitor can hold a hazardous electrical charge even after the power is off.

• The unit hums but the fan will not spin on its own -- capacitor testing and replacement, and fan-motor diagnosis, are professional work.
• The fan only starts after a push -- report that pattern to the technician rather than relying on it.
• You already had a capacitor replaced and the fan still will not spin -- the remaining possibilities (fan motor, contactor, wiring, wrong capacitor, or a control issue) all need a professional.

You can hear or feel the indoor air handler running, but the outdoor condenser and its fan never kick on, so the air coming from the vents is not cold.

When the indoor side runs but the outdoor side does not, the issue is often in the path that tells the outdoor unit to start: the contactor not pulling in, a missing 24-volt control signal, a relay, or a break in the power or control wiring between the thermostat and the condenser.

• Confirm the thermostat is set to Cool and is actively calling for cooling (the setpoint is below room temperature).
• Note whether the outdoor unit appears to have lost power or whether a breaker is already tripped, and tell the technician.

• Do not push, tap, or hold the contactor closed, and do not touch any electrical component inside the unit -- these are live parts.
• Do not jump or bridge any wires.
• Do not open or work inside the electrical panel, and do not operate the outdoor disconnect as a troubleshooting step.

• The indoor air handler runs but the outdoor unit stays off -- low-voltage, contactor, relay, and control-path diagnosis is electrical work for a licensed technician.

The outdoor fan runs slowly or unevenly, cuts in and out, stops after running a while, or you notice unusual heat coming off the outdoor unit. In some cases the compressor keeps running while the fan is stopped.

A slow, intermittent, hot, or stiff fan often points toward the condenser fan motor itself -- worn bearings, overheating, or a motor shaft or blade that is binding. Running the compressor with the fan stopped can let the outdoor unit overheat, because the fan is what carries heat away from the condenser.

• If the fan is stalled, running slowly, or the motor is overheating, switch the system off so it is not running without proper airflow.
• From a safe distance, and without reaching into the unit, note whether obvious debris is visible in the fan.

• Do not keep running the system with the fan stopped or stalling.
• Do not spin the fan by hand or try to free it.

• The fan is slow, intermittent, hot, seized, or hard to turn -- fan-motor, bearing, wiring, and overheating diagnosis is professional work.
• The compressor keeps running while the fan is stopped -- switch the system off and arrange service to avoid overheating damage.

The fan will not turn freely, a blade looks cracked, bent, or torn, the fan hits the shroud or guard, or the unit rattles and shakes when it tries to run. Sometimes this follows leaves, twigs, or a broken guard getting into the unit.

A physically damaged, bent, or stuck blade, debris jammed against the blade, a restrictive leaf guard, or an out-of-balance fan after earlier work can all stop the fan or make it unsafe to run. Severe vibration can damage the motor shaft and mount.

• Switch the system off at the thermostat and leave it off before you look at the unit.
• From outside the unit only, look for a broken or bent blade, or obvious loose debris such as leaves or twigs against the fan.
• Clear only loose external debris you can reach from outside, without removing any panel or guard and without reaching into the unit.

• Do not reach into the unit, and never reach into a unit that still has power to it.
• Do not run the system with a damaged blade or a blade that is rubbing or hitting the guard.
• Do not remove the fan guard or any panel.

• A blade is broken, bent, cracked, or rubbing, the fan is out of balance, or the unit shakes hard when it runs -- blade, motor-shaft, and balance work is professional.
• Debris is packed in past what you can safely clear from outside, or a guard or mesh is restricting the fan.

The outdoor unit is completely off, and when you look you find a breaker for the air conditioner already in the tripped position, or the unit otherwise appears to have lost power.

A breaker that has already tripped, or a breaker that trips immediately or repeatedly, usually points toward an electrical fault -- a short, an overcurrent, or a locked motor or compressor drawing too much current. This is a protective device doing its job, not a nuisance to override.

• Note whether the outdoor unit appears to have lost power or whether a breaker is already tripped, and tell the technician what you found.
• Leave the system switched off at the thermostat until it has been checked.

• Do not reset the breaker if there are any electrical/burning hazard signs or if it has already tripped/retripped. With no hazard signs and no prior repeat trip, one reset after thermostat OFF is the maximum. Do not operate the outdoor disconnect.
• Do not reset a breaker repeatedly to try to force the system to run.
• Do not open or work inside the electrical panel.

• A breaker is already tripped, or trips again after the system is switched off and left alone -- an electrician or HVAC technician needs to find why before the unit is used again.