Why Is My ecobee Not Turning On The A/C?


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Nothing coming out of the air vents? Or is the air that’s blowing not cold? 

If you’re wondering why your ecobee is not turning on the air conditioning, you’ve come to the right place. 

There are several main reasons why your ecobee smart thermostat won’t turn on the Air Conditioning (A/C). In this guide, I detail the troubleshooting steps that can help you get your air conditioning back under the control of your ecobee smart thermostat. 

This article covers all the main ecobee thermostat models, including the ecobee3 Lite, ecobee4, and the ecobee SmartThermostat. Where there are steps that are specific to a particular model, I will make special note of them.

The problem may not lie with your ecobee thermostat, but with your air conditioner system itself. In this first section, I discuss some steps you can take to get a problematic A/C system back up and running. 

If your ecobee is not cooling to the set temperature, you can also troubleshoot with these steps here. The issues may crossover here.

Troubleshooting A/C issues

Many air conditioner problems are caused by excess water build-up caused by condensation within an HVAC system.

All HVAC systems have a primary drain line or drain pan. These can get dirty and clogged up over time. Drain clog issues can cause a build-up of condensation. If the water level reaches a preset maximum limit, then a switch will kill the power to the boiler and the thermostat. 

Symptoms of this issue could be: – 

  • Puddles or other signs of moisture around the air conditioning unit.
  • The ecobee thermostat frequently reboots. Or it powers off and the ecobee won’t turn on.
  • The drain pan is full or overflowing.
  • Signs of corrosion or other water damage around the drain pan or drain line.

If you have a removable drain pain, do keep an eye on it once in a while to prevent water from accumulating that could lead to mold buildup. 

If any of these symptoms appear to be affecting your HVAC system, then follow the troubleshooting steps below. 

Important: Before you proceed, ensure that the main power to your HVAC system has been turned off. This should be turned off from your home’s main breaker box. If this is something you’re not comfortable with, you will want to hire a HVAC technician.

Step 1 – Locate the Drain Pan, Evaporator Coils, and Condensate Drain Line

Depending on your HVAC system, these may be located in different places. On some models, they might be on top or bottom of the furnace, and some even have them on either side or possibly on the ground.

The drain line (drain pipe) is normally a PVC pipe (usually white) and can be found on the side of your furnace. 

One other thing to note is that if your HVAC system is in the attic, then it is highly likely that there will be two drain pans. Normally, there will be the main drain pan directly under the evaporator coil, and a further backup pan that is usually found underneath the air handler. 

Step 2 – Clear the Condensate Drain Line of Any Blockages and Empty the Drain pan(s)

If the backed-up drain pan is full or nearly full, then empty it of water and thoroughly clean it. The condensate drain line should also be flushed to clear any blockages.

There are several methods to do this, which are listed below. But if you are not comfortable with DIY, then a HVAC technician can perform this task. 

1. A stiff, thin brush can be pushed into the end on the condensate drain line, this will clear any blockages that are close to the end of the drain tube. 

2. Locate the vent tee that connects the drain line to the drainage tray. Remove the PVC cap from this and pour a 50/50 water and bleach solution into the drain line. Leave it in for thirty minutes. Check to see if water has drained out of the line.

3. Use the thin brush to clear any debris from the vent tee side.

4. If it is still blocked, then a wet and dry vacuum cleaner with the nozzle duct-taped onto the drain line can be used to try and suck the debris from the rube.

Step 3 – Find and Reset the Float Switch to Check It’s Working

Often the float or safety switch will need to be reset before the HVAC system will function. Normally these are located beside the drain pan or close to the bottom of the furnace or handler.

If you can’t locate the switch, then check the “R” terminal on your HVAC system’s control panel. This is where the safety switch is normally placed. It is possible to follow the wire from this terminal to the safety switch. 

Once you have followed these steps and the drain pan is emptied of any excess water, then you can try switching on the system again. 

Troubleshooting ecobee Thermostat Issues

While the previous section focused on your HVAC/air conditioning system, this section focuses on potential issues with the ecobee thermostat itself.  I’ll explain some issues that can stop your ecobee from turning on the A/C. 

Step 1 – Check the ecobee Thermostat Wiring

We’ll start with looking at potential wiring issues with the ecobee thermostat wire bundle. Loose wire connections could easily stop the A/C from turning on.

Remove your thermostat from its wall housing. The wiring terminals will now be exposed.

The crucial wire to check is the “Y” wire. It is this wire that is responsible for switching the external A/C compressor on. Give this wire a gentle pull to ensure it is connected properly. 

Also make sure no wires are in the wrong terminals. The wiring can get confusing, so you can look at the thermostat installation wiring diagrams on ecobee’s site

Note: If you have used a Power Extender Kit (PEK) with the ecobee3 Lite or ecobee4 thermostat, then this wire will not be present. This is normal and in these cases, double-check there are no issues with wiring that does exist. 

Step 2 – Check the Wiring at your Furnace or Air Handler Unit

Once you’ve confirmed the thermostat wiring is all okay, then the next step is to check the wiring at your HVAC furnace or air handler control board.

Once again, the “Y” wire is important here. Check that it is terminated properly, and is the same “Y” wire that is connected to your thermostat. If there are any wire splices on the “Y” wire, these should also be carefully checked. 

There should also be two separate wires coming from the external compressor. One of these wires should be connected to the “Y” terminal, the other should be connected to the “C” terminal. Check that both of these wires are securely fitted. 

Step 3 – Check your configuration

If you are happy that the wiring is all okay, then the next step is to check the configuration of the equipment. 

Note: This step does not apply to ecobee3 Lite or ecobee4 thermostats that are wired using a PEK. 

To check the configuration, use the ecobee app or access the menu on the thermostat and navigate to the following section. 

Settings –> Installation Settings –> Equipment –> Wiring

You should see both the RC and RH highlighted. If only one wire shows as being connected to the RC terminal on the thermostat, this will require reconfiguring. 

You should also see the Y1 option highlighted. If it isn’t, then this will need to be reconfigured. The steps for this are detailed below.

Step 1 – Using the app or thermostat screen, navigate to Settings -> Installation Settings -> Equipment -> Reconfigure Equipment

Step 2 – The first screen will ask if you have one or two wires connected to the R terminal. (Two wires are RC and RH). If there is only one wire connected then select “Yes, only RC is connected.” If an RC and RH wires are connected then select, “No, RC and RH are connected.”

Step 3 – The next screen will display all the detected wires. The Y1 wire should be highlighted. If it isn’t, then select “No” when asked if the wiring looks correct.

Step 4 – Select the Modify option and manually select the Y1 terminal. Step through the rest of the process. 

Step 5 – There should now be an option for Air Conditioner displayed. Open the Wiring Menu from the Equipment screen and you should see Y1 selected. 

Step 4 – Check the Threshold Settings

Navigate to the following section using the app or from the thermostat. 

Settings -> Installation Settings -> Thresholds

In this section, there are a couple of settings you need to check. 

1. Compressor Minimum Outdoor Temperature – The outdoor compressor unit will not run if the outside temperature is below this setting. Adjust the temperature lower if needed.

2. Compressor Minimum Cycle Off Time – This is the least amount of time that your compressor will remain off between run cycles. By default, the minimum compressor cycle time is set to 5-minutes (300 Seconds). If your compressor has completed a cycle within the stated period, it won’t power on until this period has elapsed. 

If you are still having issues after following the steps in this guide, then contact the ecobee support desk. If you’re not as comfortable dealing with HVAC units, do call a HVAC technician. 

For more ecobee guides and troubleshooting articles, check these out: