Symptoms
- AC suddenly stops running with no other obvious symptoms
- Thermostat may still show a call for cooling but nothing happens
- Condensate drain pan is full or overflowing when checked
Likely causes
- CommonClogged condensate drain line causing the pan to fillWhen the pan can't drain, it eventually fills enough to trip the float switch as designed.
- PossibleFloat switch stuck or misalignedA switch can occasionally stick in the tripped position even after the pan is emptied.
- PossibleFailed condensate pump backing water up into the panIf a pump normally removes water and it fails, the pan fills and trips the switch.
What to do
- Locate the condensate drain pan, usually near or under the indoor air handler, and check if it's full of water.
- Clear the condensate drain line as described for a clogged AC drain, since this is almost always the underlying cause.
- Once cleared, check that the float switch resets on its own or manually reset it per the manufacturer's instructions.
- If there's a condensate pump, check that it's running and its float moves freely.
- Empty the pan of standing water once the drain is clear, and restart the system.
- Never bypass or disable the float switch, since it's protecting your home from water damage.
Tools and parts
- Wet/dry shop vac
- Bucket
When to call a pro
Call an HVAC technician if clearing the drain doesn't resolve the trip, or if the float switch or condensate pump needs replacement.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.