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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8373
Experience:  Furnace, A/C and heat pump specialist.
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I purchased an ecobee3 thermostat apartment. The installed

Customer Question

I purchased an ecobee3 thermostat for my apartment. The installed wiring was 4 wires, Red, Green, White, and yellow. Unfortunately I cannot get to the HVAC control board to connect the common, or the PEK that came with the ecobee. In order to get around this I connected an external transformer to the "C" and the "Rc" terminal on the ecobee. With the red wire from the equipment to "Rh". Everything powered up normally, after the ecobee calibrated, it rebooted itself then calibrated again. Once it finished calibrating the second time, it did not control my equipment at all. What have I done wrong?
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.
Hello. My name is ***** ***** I'll do my best to help. Let's get started and see what we can do.Most of the ecobees do not work properly using an external transformer. WEre you told this was an option?
Customer: replied 2 years ago.
No. Just wishful thinking.
Expert:  airheatman replied 2 years ago.
The best alternative for you using the Ecobee if you don't have a C wire, is to sacrifice the FAN ONLY mode by stealing the green wire fron G and using it for C. To do this, move the wire from G over to C at both thermostat and indoor unit. Also you need to add a jumper in unit from Y to G so fan is energized in Cool mode.
This provides a common, but you sacrifice the FAN ONLY option since we no longer have a wire for G.