Let's walk through this methodically. First, you need to verify the thermostat is sending the correct signal.
- On the thermostat, press Menu > System Mode. Make sure it's set to Cool and press Done.
- Set your desired temperature to be lower than the current indoor temperature shown on the screen. The system needs a reason to turn on.
- Go listen at your outdoor AC unit. You should hear it start within a few minutes.
If you don't hear anything:
- Check your home's circuit breaker for the HVAC system and reset it if needed.
- Make sure the power switch at the outdoor condenser unit and the indoor furnace/air handler are both ON.
- Ensure the furnace door is closed completely.
- Wait a full 5 minutes. Many systems have a built-in delay to protect the compressor.
If that didn't work: The issue might be with the wiring connection. Go back to your installation photo. Verify the Y wire (for cooling) is firmly inserted into the Y-terminal on the thermostat wall plate and the corresponding terminal on the furnace control board.