I'm attempting to install a new ecobee3 on an older Coleman Evcon gas furnace and AC HVAC system. The system is what I would consider typical residential as far as I can see. There is currently a Honeywell RTH2410B1001 programmable stat installed and (seemingly) functioning as expected. The wiring at the thermostat is the typical Y R G W wiring (actual wire colors also match the terminal label designation).
When I went to install the ecobee3 PEK module, I noticed that the yellow wire (the thermostat Y terminal) is connected directly to the HVAC control board C terminal, and the control board Y terminal is empty. The other wires (R, G, W) are as expected.
I'm not sure what to do at this point. I'm reluctant to simply follow ecobee's instructions (waiting for their support to call me back with with more information) for connecting the PEK module wires to the corresponding control board terminals, and then plugging in the stat wires to the terminal board on the PEK module based on the thermostat wiring (essentially ignoring the fact that Y -> C).
Also, I just don't understand how the AC compressor relay is energized and functions if the Y stat terminal is sent straight to common. (I found the splice up in the drop ceiling between Y and the AC compressor relay).
Any help anyone could provide would be much appreciated.