Symptoms
- Set to Cool but no cold air
- Outdoor unit not running
- Indoor fan may or may not run
Likely causes
- CommonWrong mode or set pointCool mode must be selected and set below the current room temperature.
- CommonTripped breaker at the outdoor unit or air handlerAC systems have dedicated breakers that can trip independently.
- CommonFull condensate drain pan tripping a float switchMany systems shut off cooling automatically to prevent water damage when the drain pan fills.
- PossibleShort cycle delay after a recent power lossCompressors often wait a few minutes after power returns before restarting.
- PossibleFailed capacitor or contactor at the outdoor unitThese small parts commonly fail and prevent the compressor and fan from starting.
What to do
- Confirm the thermostat is in Cool mode and set at least a few degrees below room temperature.
- Wait 5–10 minutes in case the compressor is on a built-in restart delay.
- Check both the outdoor unit breaker and the indoor air handler breaker.
- Look for a small float switch near the indoor unit's drain pan and check if it's tripped from standing water.
- Clear any visible clog in the condensate drain line if you see standing water.
- If breakers are fine and the drain isn't full, listen at the outdoor unit for a hum with no fan movement, which suggests a failed part.
Tools and parts
- Flashlight
- Wet/dry vacuum (optional, for drain line)
AC condensate drain line cleanerSearch: “AC condensate line cleaning tablets”
When to call a pro
Call an HVAC technician if breakers hold, the drain isn't the issue, and the outdoor unit hums but doesn't run, or doesn't respond at all.
Safety
Use caution
Never touch components inside the outdoor unit's electrical panel; capacitors can hold a charge even when power is off.