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AC Running but Not Cooling? 6 Checks Before You Call for Service

Many 'broken' air conditioners are a clogged filter, a thermostat setting, a tripped breaker or a dirty outdoor coil. Work through the checks below first. If the outdoor fan isn't spinning or you see ice on the lines, stop and call a technician.

Verdict: Careful

Filter, thermostat and cleaning are DIY. Refrigerant, capacitors and electrical parts are for a licensed HVAC tech.

Time
20–40 min
Cost
$0–40 for DIY checks; $150+ for a service visit

Safety first: Turn off power at the outdoor disconnect before cleaning. Capacitors inside the unit hold a dangerous charge even with power off; don't open the panel.

Likely causes and how to tell

  • Dirty air filter

    The filter looks gray; weak airflow from vents. Clogged filters can even freeze the indoor coil.

  • Thermostat setting or batteries

    Set to Fan or Heat instead of Cool, or the display is blank.

  • Tripped breaker or outdoor disconnect

    Indoor fan runs but the outdoor unit is silent.

  • Dirty outdoor coil

    Fins caked with dust, grass or cottonwood; the unit runs constantly.

  • Clogged condensate drain

    Water in the drain pan or a float switch shut the system off.

  • Low refrigerant or failed capacitor

    Ice on the copper lines, or the outdoor fan doesn't spin while the unit hums. Pro only.

How to fix it

  1. 1

    Check the thermostat

    Set it to Cool, a few degrees below room temperature, fan on Auto. Replace the batteries if it has them.

  2. 2

    Replace the filter

    Match the size printed on the old filter. Replace every 1–3 months in cooling season.

  3. 3

    Check breakers

    Check the AC and air handler breakers in the panel, and the disconnect box by the outdoor unit.

  4. 4

    Clean the outdoor unit

    Turn off power at the disconnect, then gently hose the fins from the inside out. Clear 2 feet of space around it.

  5. 5

    Clear the condensate line

    Find the PVC line near the indoor unit and clear it with a wet/dry vacuum from the outdoor end.

  6. 6

    Give it an hour

    Run it for an hour and feel the air at a vent. It should be 15–20°F cooler than the room air.

What you'll need

  • Correct-size air filter
  • Garden hose
  • Wet/dry vacuum
  • Flashlight
  • AA batteries

Call a pro if

  • Ice on the refrigerant lines or indoor coil (turn the system off and run only the fan to thaw).
  • The outdoor fan doesn't spin, or the unit hums or clicks without starting.
  • A breaker trips again after reset.
  • Any refrigerant work: EPA certification is legally required to handle refrigerant.

AI Handyman writes a free job brief in trade language, so a pro can quote from your photos.

Questions people ask

How cold should the air from vents be?

About 15–20°F colder than the air going into the return. Smaller differences suggest low refrigerant or airflow problems.

Can I add refrigerant myself?

No. Handling refrigerant requires EPA Section 608 certification, and low refrigerant means a leak that must be found and repaired.

Related fixes

General guidance, not a licensed inspection. Follow local codes; when in doubt, call a licensed professional.