How can I get power to my new Ecobee thermostat?

Question

I purchased a new Ecobee smart thermostat which requires a C wire (the Nest unit did not) to power the thermostat. I located the blue C wire behind the thermostat, but it was not connected on the other end in the air handler. I located the red wire, which is connected to a safe t switch wire with an orange twist wire connector and connected the c wire with. It gave the thermostat power but would restart every time the ac was about to turn on, which it never did.

The other safe t switch wire is connected to the yellow (y) wire. I removed the safe t switch wire from the red wire but the y wire would not show as connected. I moved the wires around to different connectors and still can’t figure it out. I assuming the safe t switch is causing the issue but I don’t want to remove/bypass it.

So basically I’m trying to figure out how to get the c wire to power the thermostat, just not sure what to connect to what at this point. Any help would be appreciated!

Answer 1

Go to the source of R and C

They come from a 24 Volt transformer.

In your picture the 24 Volt Transformer is located at the bottom left.

Be aware that it has 120 Volt input so do not confuse those.

Answer 2

You have the C-wire connected to the R-wire in the air handler? And power is lost to the thermostat if the thermostat tries to run the air conditioner? If I understand this correctly then you have been shorting out the 24VAC supply to the thermostat with the thermostat. While it may be unlikely there's a possibility that the transformer has been damaged by being shorted out. This may require an electrician or HVAC installer to diagnose and repair.

Some HVAC systems will have two separate 24VAC transformers, one for heat and one for air conditioning. This is especially common if the house originally had only heating with air conditioning added later. To make the distinction between the two transformers there's often "Rh" for the heating transformer and "Rc" for the cooling transformer. By running the C-wire to one of the R-wires you may have shorted out one of the transformers while creating a return path for getting power to the thermostat from the other. When the thermostat closes the circuit for the air conditioner it could have shorted both transformers, or something, which then means the voltage to power the thermostat drops to zero and it powers off.

I'm trying to draw the possible circuits in my head given what was described and one of them tells me that it is possible the two transformers were put in series at some point, meaning what should be a 24VAC circuit had 48VAC placed on it.

One important piece of information needed to diagnose this is knowing how many 24VAC transformers there are. There's almost certainly one in the furnace, or whatever is the primary device for moving air through the system if there's cooling only or something for heat other than something that burns fuel. I don't know if there's a standard location for a 24VAC transformer on air conditioners so I can't really tell you where to check. If there's a humidifier, dehumidifier, or some other accessory device in the HVAC there may be a third 24VAC transformer.

If the thermostat is going dead when it tries to run the air conditioner then there could be a short circuit somewhere, maybe an overloaded transformer (too much load and the voltage drops), or something else bad that could damage something. It is possible nothing has been damaged, at least not yet. Keep guessing on the wires and I expect it won't be long before something expensive breaks.

If you don't want to call in a professional just yet then slow down and connect each device one by one. Perhaps try connecting just the air conditioner first, and make sure that runs as it should. Then add the furnace, check that works. Then add the humidifier or such if there's anything else, then check that.

Most HVAC installers will come out on short notice but they charge extra for that. If you can get the important bits running temporarily (as in keeping the place safe and comfortable for the next day or so) so the pros come out on a scheduled visit, versus an "emergency call", then they charge a lower rate.

I realize that "call a professional" answers are discouraged here but this might be one of those exceptions.

Answer 3

In the most basic form, the red "R" wire connects to one side of a 24 volt transformer and the blue "C" wire connects to the other side of the transformer. Often the C is connected to the chassis of the furnace/air handler as well, though maybe this is more common with gas-fueled furnaces than with electric air handlers.

The yellow "Y" wire controls the cooling while the white "W" wire controls the heating. Often there's a green "G" wire too; this one controls the blower. The thermostat calls for any of these functions to run by shorting them to R. Cooling mode often requires that both Y and G be activated -- Y turns on only the compressor, which will quickly turn the evaporator into a block of ice if the G is not used to activate the blower.

Yours is equipped with a safe-t-switch. As you noted, this is just a type of float switch whose purpose is to disable equipment when condensate water rises too high. You can choose how you want this to work. Do you want to cut power to the thermostat so that it's obvious something is wrong? Wire it in series with the R connection. Do you prefer to let the thermostat and the blower stay on, and only shut down the condenser if the condensate rises too high? In that case wire it in series with the Y.

When I do a condensing fuel-burning furnace and an air conditioner which both use a condensate pump to get rid of the water, I wire the float switch in series with the R. This ensures that both heating and cooling are shut down if the pump fails.

Your description of finding the safe-t-switch connected to R and Y is suspicious. Consider whether the wire colors might not match convention, or whether it's possible your observation of the original connection might be mistaken.