I am having issues properly installing an ecobee SmartThermostat with voice control. My HVAC system is forced air with gas furnace, AC and HRV. The HRV is hooked up to the furnace board using the interlock wiring displayed on the right side of the attached screenshot.
I got the ecobee thermostat to better control heating, cooling and the fan and wanted to leave the HRV control separate. So I left the interlock wiring as-is, connected the C wire at the thermostat (yellow wire in the attached photo) to the board (it was originally not connected as the old thermostat ran on battery), and followed the standard ecobee thermostat wiring in the manual.
I have no issues cooling or running the HRV. However when I switch to heat or turn on the fan, the AC always turns on. I tried reaching out to ecobee support, but they could not find a solution. Any ideas before I book a service call?
Thanks very much!
Do you have the red wire connected to RC and nothing to RH?
It sounds like an interlock wiring problem, back feeding the Y wire. Can you post a picture of the wiring at the furnace, HRV and the interlock wiring?
Here are photos of the wiring. In the wide shot of the board, you can see on the left two bundles of wires - one upper tan from the thermostat and the lower brown from the HRV.
From HRV to board:
NO red to R
C darker green to G
NC white connected to thermostat wire G lighter green
From thermostat to board:
Rc red to R
G lighter green as above
Y1 blue to Y/Y2
C yellow to C
W1 white to W
On the left of the wider shot you can also see a grey-brown bundle of wires from the AC to board:
C black to C
Y thicker white to Y/Y2
Apart from the C wire from the thermostat, this seems to be the alternate interlock wiring from the HRV manual. I am not sure what might be energizing the Y wire to activate the AC when the fan or heat turn on.
Any further thoughts would be most appreciated!
I think the issue is at the green molex plug on the HRV. Remove the red wire from the Y and move it to R.
Thanks for the suggestion! I tried it and...
- Power is cut from the HRV wall control, so I can't turn it on.
- I did a test run of the fan from the ecobee settings and the AC still turned on.
Actually my mistake, the Deco control uses the R and 4 wires. The Lite touch control uses Y, G and B like you had it. Sorry about that!
There's a setting in the Ecobee MAIN MENU > SETTINGS > INSTALLATION SETTINGS > EQUIPMENT > FURNACE > FAN CONTROL IN HEAT MODE. Is yours set to have the Ecobee or HVAC control the fan? Set it to HVAC and see if the AC still starts on a call for heat.
Start by double checking all the Ecobee settings. Make sure it's set for a gas furnace and not electric and AC not a heat pump.
Otherwise, your interlock wiring looks good but I would eliminate it and see if the problem stops.
Disconnect the green and white wires from the interlock connection (remove orange wiring connector). Remove the green wire from furnace G and connect the Ecobee G wire directly to it. Tape up the ends of the abandoned white and green HRV wires while you test. Now that the interlock wiring has been eliminated see if the AC still starts with a call for heat or continuous fan.
Originally you said you have no issues with the cooling or running the HRV. Does that mean when you start the HRV the AC does not also start? The interlock should have started the furnace fan the same way turning the Ecobee fan on does. But if I'm understanding correctly, the AC only starts when you turn the fan on using the Ecobee, or with a call for heat. The heat does not start when you turn on the AC?
I normally see this problem when the HRV uses the 2 wire interlock method, and the 3 wire method that you use fixes the problem. Sometimes the stat or control board will jumper Y and G and this is what I'm thinking is allowing the AC to start. 24V on G is back feeding to Y somehow. It could be a faulty thermostat or setting issue, faulty furnace control board or wiring issue.
We should be able to narrow it down.
Thanks for persisting with this!
Just to clarify the issue:
- AC turns on when I try to run only the fan through the ecobee controls.
- AC turns on when I switch to heat or test run heat through ecobee controls.
- AC does not turn on when I turn on the HRV using its separate wall control.
I don't think when the AC is running, the heat is also running based on the sounds from the furnace and the vent temperature - lower than 15C. But if there is a way to confirm this, I would be happy to learn more.
I did try to rewire according to the standard interlock diagram from the HRV manual (left side of the screenshot). That is, remove the marrette connecting thermostat G wire and HRV NC wire, connect thermostat G wire to G on the board. The above problems persisted, and further the AC would start when I turned on the HRV. If I remove the HRV C wire from G on the board, won't this mean the HRV would run without the fan?
I went back through the ecobee settings, switching to HVAC for fan control in heat mode. This resolves the problem of the AC turning on when I test run heating. Test run of only the fan still turned on the AC, though, but this is some progress!
That's good news the heating issue is resolved.
When the HRV is turned on it powers furnace G and starts the furnace fan, and the AC doesn't start.
And when you turn the Ecobee fan on and energize furnace G the furnace fan starts but the AC also starts. This is strange but means something is powering Y. I wonder if there is some dehumidification setting in the Ecobee. It may be worthwhile doing a factory reset on the Ecobee so all the settings are reset.
I'm thinking the issue is with the thermostat or settings, or the thermostat wire itself may have a short between G and Y. A continuity test between these 2 wires would rule this out.
When you turn the Ecobee fan on, and the AC starts, does the Ecobee report that the AC is running? Or just that the fan is running?