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Air conditioning · triage

AC running, but not cooling

The short answer

Usually this week, sooner in dangerous heat. Check the thermostat, the filter, the outdoor unit’s breaker and fan, and look for ice on the copper lines. Refrigerant and electrical parts are licensed work.

Heat can be the emergencyIf the house is dangerously hot for an older adult, a baby or someone with a health condition, get them somewhere cool first. The repair can wait; they can’t.

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

WatchA thermostat setting

Give it 30 minutes.

  1. Leave it on Cool, below room temperature
  2. Check the vents are blowing cool air after 15–30 minutes
  3. If not, go back through the checks
This weekIced coil or lines

Turn cooling off and let it thaw.

  1. Set the thermostat to Off and the fan to On Running the fan alone helps the ice melt.
  2. Replace a dirty filter and open closed vents Restricted airflow is a common cause.
  3. If it ices again, call a technician Low refrigerant or a failing blower also cause icing; both are licensed work.

Ice forms when not enough warm air crosses the coil (dirty filter, closed vents, weak blower) or the refrigerant charge is low.

This weekThe outdoor unit isn’t running

Check the breaker once. Then it is a technician job.

  1. Check the AC breaker in the panel and the disconnect box by the unit Reset a tripped breaker once by switching it fully off, then on.
  2. If it trips again, leave it off Do not open the disconnect box or the unit’s panels.
  3. Call an HVAC technician A failed capacitor or contactor is common and usually a quick repair.
This weekUnit hums but the fan won’t spin

Turn it off to protect the motor; call a technician.

  1. Turn cooling off at the thermostat Running a stalled motor can damage the compressor.
  2. Clear debris from around the unit Keep 2 feet clear; don’t reach into the fan.
  3. Call an HVAC technician A failed run capacitor or fan motor is the usual cause.
This weekStart with the filter

A clogged filter is the most common cause.

  1. Turn the system off and replace the filter Match the size printed on the old one. Note it in your record.
  2. Hose the outdoor coil gently from inside out if it is matted with debris Power off first at the disconnect or breaker.
  3. Run it for an hour If the air is still warm, call a technician.

ENERGY STAR suggests checking filters monthly in cooling season; a dirty filter cuts airflow and can freeze the coil.

This weekIt needs a technician

Book this week; sooner in extreme heat.

  1. Note what you checked Thermostat, filter, breaker, fan, ice. It saves diagnostic time.
  2. Close blinds and use fans meanwhile
  3. Ask the technician for a written diagnosis before repairs Then run any replacement quote through Quote Check.

Most no-cool calls are a failed capacitor, low refrigerant (a leak), a dirty coil or a failing compressor. Don't add refrigerant yourself; it is licensed work.

Related

Frozen AC coil or iced refrigerant linesAC leaking water insideBreaker 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 thermostat on Cool, set below room temperature, with the fan on Auto?