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Air conditioning · triage

Outdoor AC unit not running

The short answer

Check the thermostat, then the AC breaker and the disconnect switch by the unit, once. Anything inside the unit (capacitor, contactor) holds a charge and is technician work.

Capacitors hold a chargeEven with the power off, an AC capacitor can shock you. Do not open the unit’s service panel.

Know your shutoffs

Electrical panel and main breakerThe breaker panel (or fuse box), often in a garage, basement, utility room or hallway.

Every outcome on this card

WatchBack on after one reset

Watch for a repeat.

  1. Log the date
  2. Keep 2 feet clear around the unit
  3. If it trips again, leave it off and call
This weekThe breaker trips again

Leave it off; technician this week.

  1. Leave the breaker off Repeated resets can damage the compressor or wiring.
  2. Use fans and close blinds
  3. Call an HVAC technician
This weekPower is on, the unit doesn’t start

Book a technician this week.

  1. Confirm the thermostat calls for cooling Set it 5°F below room temperature.
  2. Don’t open the unit Capacitors store a charge.
  3. Call an HVAC technician Failed capacitors, contactors and thermostat wiring are common, usually same-day repairs.

Related

AC running, but not coolingBreaker keeps tripping after you reset it

Written from

Original casaq guidance, updated 2026-10-05. General guidance, not a diagnosis; licensed-pro review pending. Severity levels: Emergency now / Today / This week / This month / Watch. Send a correction.

Step 1

Is the AC breaker (often a double breaker labeled AC or condenser) tripped?