AC Running But Not Cooling: What to Check

Updated October 13, 2026 · by Aurora Star Tech Inc.

AC running but not cooling? Start with the thermostat, the filter, the breakers and the outdoor unit. Ice on the pipes, a silent outdoor unit or warm air from the vents usually means it is time for a licensed technician.

Homeowner with a air conditioner problem? Call (647) 657-2977 or book a service call — licensed technicians across Vaughan and the GTA.

Common reasons: ac running but not cooling

Thermostat set to Fan On or the wrong mode
Clogged filter or blocked return vents
Outdoor unit off: tripped breaker or disconnect
Dirty outdoor coil or debris around the unit
Frozen indoor coil from low airflow or low refrigerant
Failed capacitor or contactor (outdoor unit hums or does not start)

Safe checks you can do yourself

Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
Check both breakers and the outdoor disconnect box beside the outdoor unit; all should be ON.
Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
Keep about 2 feet around the outdoor unit clear of leaves, grass and debris.
If you see ice on the pipes or the indoor coil, turn the system off and run only the fan for a few hours, then call a technician.
Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

When to call a licensed technician

Ice on the copper lines or indoor coil
The outdoor unit is not running or only hums
The breaker trips again
Cooling is weak even with a clean filter (possible refrigerant leak)

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Showing an error code? Look it up by brand

Bosch Heat Pump Carrier AC Carrier Heat Pump Fujitsu Heat Pump Goodman AC Goodman Heat Pump Gree Heat Pump ICP Heat Pump KeepRite AC KeepRite Heat Pump Kinghome Heat Pump Lennox AC Lennox Heat Pump Midea Heat Pump Mitsubishi Heat Pump Rheem Heat Pump Trane AC Trane Heat Pump

Detailed troubleshooting guides

Not cooling All brands · Air Conditioner
Amber STATUS or green COMM light not on Carrier · Air Conditioner
Compressor will not run - winding and electrical checks - Carrier split systems Carrier · Air Conditioner
Delay before the compressor restarts Carrier · Air Conditioner
Hissing from the outdoor unit after it shuts off Carrier · Air Conditioner
Outdoor unit unresponsive after several faults Carrier · Air Conditioner
Superheat too high or too low on TXV system - Carrier split systems Carrier · Air Conditioner
Two-stage unit not changing stages - Carrier 24ANB/25HNB/25HCB6 Carrier · Air Conditioner
No cooling - R-32 GLXS/ALXS condenser Goodman · Air Conditioner
Checking OAT and OCT thermistors - KeepRite C4A3/CXA6 KeepRite · Air Conditioner

Ac running but not cooling: questions homeowners ask

Why is my AC running but not cooling?

Most often the filter is clogged, the outdoor unit is not running, or the coil has frozen. A refrigerant leak or a failed capacitor are common causes a technician has to fix.

What should I do if my AC is frozen?

Turn cooling off and run only the fan for a few hours to melt the ice, replace the filter, then call a technician if it freezes again.

Can I add refrigerant myself?

No. Refrigerant work needs a licensed technician, and low refrigerant means there is a leak that has to be found.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.