A Nest thermostat may show Cool but delay the compressor, stay in Eco, or have an equipment setting that does not match your AC. The thermostat can call for cooling, but it cannot fix mechanical AC problems.
These steps apply to Nest Learning Thermostat, Nest Thermostat 2020, and Nest Thermostat E connected to central AC or a heat pump.
Does this affect you?
Use this if you set a cooler temperature and the AC does not start, or air blows without cooling the house.
Check mode, Eco, and compressor delay
- Tap the thermostat display.
- Confirm the mode is Cool.
- If it is Heat, Off, or Heat-Cool, switch to Cool.
- Look for Eco mode or the leaf icon.
- Select Cool and your desired temperature to override Eco if needed.
- Set the target at least 3 degrees below the current room temperature.
- Wait a full 5 minutes after changing settings.
Nest protects AC compressors from rapid cycling, so a short delay after recent cooling is normal.
Check equipment profile and outdoor unit
- Open the Google Home app.
- Tap the thermostat.
- Go to Settings > Equipment.
- Confirm the system type matches your actual central AC, heat pump, or dual-fuel setup.
- Go outside and check whether the condenser runs when cooling is active.
- Check the AC breaker and outdoor disconnect switch.
- Look for a condensate drain safety switch if your system has one.
If the outdoor unit is silent while Nest is calling for cooling, the issue may be the AC unit, breaker, disconnect, drain safety switch, or control wiring.
When it is an HVAC problem
If air blows but is not cold, suspect refrigerant, compressor, coil, or airflow issues rather than the thermostat. If the system cools briefly and stops, compressor overload protection may be tripping.
Some Nest models show an error when the Y cooling wire is loose or missing. Before checking wiring, shut off power at the AC disconnect and breaker if needed, then photograph the existing connections. Do not open or service the outdoor condenser yourself; refrigerant and high-voltage parts require a licensed HVAC technician.
Sources
- Google Nest Help – Nest Thermostat isn’t cooling (2025)
- Google Nest Help – Nest Thermostat equipment settings (2025)
- Google Nest Help – Nest Thermostat compressor protection (2025)