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Ecobee4 installation with Honeywell EIMs

chezchez Dallas, TXMember
edited December 6 in ecobee

I'll start by saying I'm a complete novice when it comes to HVAC, so anything I'm saying here has been learned from the interwebz in the last 2 days.

We just moved into a new house (new to us - built around 4 years ago) and want to replace our existing Honeywell thermostats with Ecobee4s (already bought).

Upon removing the existing thermostats from the wall, there were only 3 wires (labelled 1, 2 and 3 on the wallplate. Data, R and C on the back of the thermostat itself).

After some googling, it seems that we have EIMs installed on the furnaces in the attic.

We have 2 separate units (upstairs and downstairs, both in the attic).

From what I've read, it would seem that we will need to bypass the EIMs and wire directly from the thermostats to the units. The wires are all there in the wall, so that shouldn't be TOO hard (I think).

The two systems seem to be identical with the exception of a box on the ducting on the one on the left (as you enter the attic), which has wires going into it. I have no idea what this is, whether it complicates things or if it's something we'd lose the functionality of with an Ecobee?)

I have taken pictures of the wiring as best I can and would appreciate if you guys/gals could give me any assistance in getting this working (or just tell me that I need to return the Ecobees or call a pro).

Thermostat - https://imgur.com/a/Vw5mR
Left Unit - https://imgur.com/a/KKxX8
Right Unit - https://imgur.com/a/wcxNE


  • kevinmcckevinmcc Macomb, ILMember

    Everything is straight forward for the right unit. Match the wire colors. Brown is dehumidification which will go to ACC++ and then set the accessory to dehumidifier. The rest is Yellow to Y1, White to W1, Green to G, Blue to C, Red to Rc.

    The left unit is nearly the same, except you have a choice of ventilation or dehumidifier. Since you have dehumidifier for right unit, you may want to choose ventilation.

    For ventilation, connect all three Blue wires together for C. The Green going to the damper connect to Brown wire going to the thermostat. The Brown will go to ACC++ and set the accessory for ventilation. The other Brown from the furnace do not use, just cap off. The rest is Yellow to Y1, White to W1, Green to G, Blue to C, Red to Rc.

    Discard all jumpers, they won't be needed.

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