My air conditioning won't turn on! How can I troubleshoot?

This article applies to the ecobee3, ecobee3 lite, and the ecobee4


Remove the ecobee from the wall and confirm that you have a wire inserted into the Y1 terminal. This terminal is responsible for engaging your outdoor compressor, so you will need to have your Y wire securely connected to this terminal for your air conditioning to work. Give the wire a gentle tug to ensure that it's secure.

* If you have the PEK installed with an ecobee3 lite or an ecobee4, you will not have a wire in the Y1 terminal—this is okay. We recommend double-checking all of the wire connections to ensure they are securely connected to their terminals just to be safe.

If the wiring at your ecobee is correct, double-check the wiring at your furnace/air handler control board. Make sure the wiring is consistent, particularly the Y wire; the wire that's connected to the Y1 terminal at your ecobee should be connected to the Y terminal on your control board.

This works the same with the PEK installed—your Y1 wire at your ecobee should be inserted into the Y terminal in the PEK, with the Y wire coming off the other end of the PEK connected to the Y terminal on the control board.

If you have any splice points on your Y wire, double-check to ensure that all splice points are secure. 

You'll also want to ensure that the two wires coming from your outdoor compressor unit are connected. These two wires will come from a wire bundle that's separate from the thermostat wire bundle—one of these wires should be connected to Y, the other should be connected to C. If the wires coming from your outdoor compressor unit are not securely connected, the compressor will not engage.

You can check your equipment configuration by going into:


* If you have the PEK installed, ignore these steps. Your equipment configuration will be different with a PEK installed.

1) Do you see both RC and RH highlighted? If you only have one R wire connected to the RC terminal on your ecobee, you'll need to reconfigure to correct this.

2) Do you see Y1 highlighted? If you don't, you'll need to reconfigure to correct this. 

To reconfigure your equipment, go to:


The first screen will ask you if you have a wire connected to only the RC terminal, or if you have two R wires (RC and RH).

  • If you only have one R wire connected to your ecobee, select "Yes, only RC is connected"
  • If you have both an RC and an RH wire (this means you have separate heating and cooling systems, such as a boiler and an air conditioner) select "No, RC and RH are connected"

Next, the ecobee will display all of the detected wires. Check to see if Y1 is highlighted—if it isn't, select "No" in the bottom left corner when it asks you if the wiring is correct.


You will see the option for "Modify" in the bottom right corner—select this, then manually select the Y1 terminal. Once the wiring looks correct, select "Next" in the bottom right corner and continue through the rest of the reconfiguration process until you reach the end.

y1-2.png y1-3.png

You should now see the option for Air Conditioner under the EQUIPMENT screen. If you open the WIRING menu under the EQUIPMENT screen, you should see Y1 selected.

y1-4.png y1-5.png



Compressor Minimum Outdoor Temperature. Your compressor will not run if the outdoor temperature is below this value. Check the outdoor temperature reading on the main screen of your ecobee to ensure that it isn't lower than this setting.

Compressor Minimum Cycle Off Time. This is the minimum amount of time your compressor will remain off between cycles. This is set to 300 seconds (5 minutes) by default. If your ecobee has completed a cooling cycle, it will wait at least 5 minutes (or whatever you've set this value to) before turning the compressor on again. Once this time has elapsed, your compressor should turn back on.
A tripped float switch is usually accompanied by rebooting during a call for cooling which may result in a loss of power completely. Inspect your float switch/condensation pump/drip pan (located at the furnace) to see if there's an excess of water or any blockage preventing the water from draining.


If you've followed all of the troubleshooting steps above and your air conditioner still isn't turning on, please reach out to our Support team for further assistance.

For your convenience, when contacting Support, please have your serial number (found by going to MAIN MENU > ABOUT) handy, as well as clear photos of the following:

  • The wiring at your ecobee thermostat
  • The wiring at your terminal block/air handler/furnace board
  • The wiring at the Power Extender Kit (if applicable)
  • The wiring at any wire splice points or wire nuts/marrettes

Having these photos handy will ensure faster service and will help us identify any potential wiring issues sooner.

Was this article helpful?

Have more questions? Submit a request