Outside AC unit not running?

What usually causes this

These are the common possibilities, not a diagnosis. A page cannot tell which one it is — that takes a technician testing the system.

Tripped breaker or pulled disconnect

The outdoor unit has its own breaker and a disconnect box on the wall beside it. Either can cut power while the indoor unit keeps running.

Failed capacitor

The capacitor gives the compressor and fan motor the boost they need to start. When it fails, the unit often hums without starting. It's one of the most common AC repairs.

Failed contactor

The contactor is the switch that turns the outdoor unit on when the thermostat calls. Pitted or stuck contacts stop it starting.

Fan motor failure

If the compressor runs but the fan doesn't, the unit overheats and shuts down on its safety limit.

Compressor problem

Less common, but a compressor that won't start or keeps tripping its overload is a major repair.

What you can safely check yourself

• Check the breaker for the outdoor unit and reset it once if it has tripped.
• Check that the disconnect switch or pull-out block beside the outdoor unit is fully in place — without opening anything beyond its cover.
• Look and listen from a safe distance: is it humming, clicking, or silent? Is the fan turning? Tell the technician — it helps.
• Clear leaves, grass and plants from around the unit.

What we check when we get there

1. 1The technician tests the capacitor, contactor, fan motor and compressor rather than swapping parts until one works.
2. 2If a part has failed, you'll hear why — for example, a capacitor that failed early can point to heat or voltage problems worth knowing about.

What it is likely to cost

Capacitors and contactors are among the least expensive AC repairs. A fan motor is mid-range; a compressor is the most expensive and often prompts a repair-or-replace conversation.

Diagnostic / service call

$89

Capacitor replacement

From $179

Contactor replacement

From $189

Condenser fan motor

$449–$799

Compressor

$1,799–$3,499

Prices are starting points for standard work in the Savannah area. Final price depends on the system and site, and is confirmed before work begins. Permits and code-required upgrades may be additional.

Repair or replace?

A failed capacitor or contactor is a repair on almost any system. A failed compressor on a system past about 12 years old is where replacement deserves a real comparison.

Questions people ask about this

Why is my outside AC unit humming but not turning on?

Most often a failed capacitor or a seized fan motor. Switch the system off at the thermostat so the compressor doesn't overheat, and have it tested.

Is it safe to run just the indoor fan?

Yes. Setting the thermostat fan to On with cooling off will move air without stressing the outdoor unit while you wait for service.

Where to go next