Symptoms
- Mode selector shows Cool and won't change
- AC runs even when set to Heat or Off
- App and thermostat display disagree on mode
Likely causes
- CommonSoftware or app sync glitchThe app and physical thermostat can temporarily disagree on the active mode.
- PossibleRestricted mode setting enabledAn installer setting may lock out heat mode, common in cooling-only or warm climates.
- PossibleStuck cooling relay or contactorThe outdoor unit's contactor can occasionally stick closed.
- Less commonWiring crossfeed between heat and cool circuitsIncorrect wiring can cause cooling to run regardless of the selected mode.
What to do
- Try changing the mode directly on the thermostat and separately through the app to see which one is out of sync.
- Restart the thermostat by removing it from its base plate or pulling batteries for 30 seconds.
- Check the settings menu for any mode restriction that an installer may have set.
- Cut power to the outdoor unit at its breaker for one minute to reset a possibly stuck contactor, then restore power.
- If the AC still runs regardless of mode after a full reset, have the outdoor unit's contactor inspected.
Tools and parts
- Screwdriver
When to call a pro
Call an HVAC technician if the AC keeps running in the wrong mode after a power cycle, since the outdoor contactor may be stuck.
Safety
Use caution
Turn off power at the outdoor unit's breaker before resetting it.