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

The most common cause of your air conditioner not turning on is an excessive build-up of water from condensation within your HVAC system.

Your HVAC system has a drain pan or drain line. Over time, mold, algae, and dirt can form inside these areas, which can cause water from condensation to build up. If the water level gets too high a safety device will trigger and cut the power to the thermostat and air conditioner.

Some signs that you have a backed-up drain pan or drain line are:

  • Your ecobee thermostat is powered off or is frequently rebooting
  • Water leakages, puddles of water, or signs of moisture around the air conditioning unit
  • An overflowing or full condensate drain pan
  • Signs of water damage around the drain pan or condensate drain line


Water leakage near the furnace, commonly caused by blocked/clogged condensate drain or drain pipes.


Troubleshooting condensate drain clog issues

NOTE: Before proceeding with these steps, turn off the main power for your HVAC unit at your home’s circuit breaker box. Ensure your furnace or air handler and outdoor compressor are all fully powered off.

Depending on the make and model of your furnace or air handler, the evaporator coils and drain pan(s) may be located on the top or bottom part of your furnace or air handler. Some drain pans may also be located on the side or even on the ground.

The condensate drain line is usually located on the side of your furnace and usually consists of a white PVC pipe.

NOTE: If your HVAC unit is in an attic, you likely have two drain pans. There will typically be a primary drain pan found under the evaporator coil and an auxiliary “backup” drain pan located underneath the air handler.


If the drain pan is full, it will need to be drained and cleaned. You may also need to clear any potential clogs inside the drain pipe itself by flushing out or removing any potential obstructions inside.

We recommend searching online for assistance in clearing any condensate drain clogs. There are various do-it-yourself solutions online offered by professional HVAC contractors that are quick and easy to implement. If you’re not the DIY type, we recommend contacting an HVAC technician.

Float switches are often attached to the side of the drain pan or on the ground at the bottom of the furnace or air handler.

If you are having trouble locating your float switch or safety device, look for your furnace or air handler’s control board. These safety devices will usually have a wire connecting to the “R” terminal in some way. You can locate the float switch or safety device by following this wire.

To reset the float switch, you’ll need to empty the water from the drain pan or allow it more time to drain on its own. If you are unsure of how to empty the drain pan, there are many free resources and do-it-yourself guides available online. For help finding these guides, CLICK HERE


Troubleshooting your ecobee thermostat 

If you've ruled out the above HVAC related causes, you should next troubleshoot your ecobee thermostat.

The following applies to all ecobee thermostats except Smart, Smart SI, EMS and EMS SI

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.

If you've followed all of the troubleshooting steps above and your air conditioner still isn't turning on, please contact usat 1-877-932-6233 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.

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