Thermostat wiring question

Discussion in 'HVAC Heating & Cooling' started by RickM, Dec 14, 2009.

  1. RickM

    RickM New Member

    Messages:
    1
    Location:
    Nothern NJ
    Hi all,

    I'm in the process of planning my thermostat upgrade and have two questions regarding the wiring.

    The current (battery operated) programmable thermostat utilizes 4 wires to operate. They are: White(Heat), Yellow(Cool/AC), Green(Fan) and Red(Hot side of the 24v transformer)

    I'm upgrading to the Honeywell Vision Pro IAQ with the Equipment Interface Module (EIM). The EIM works in conjunction with the thermostat and appears to require one wire in addition to what I have.

    I just want to be sure my wiring assumptions are correct.

    The four wires I have now seem to correspond to the terminals on the Vision Pro EIM. However, the schematic looks to need a hookup from the common side of the transformer to the "C" terminal on the EIM. I assume I need to run another wire from the transformer or the control board (at the furnace) to the EIM to complete installation......correct?

    (I guess what is confusing me is that the EIM schematic shows the need for the extra (common) wire at the "C' terminal but it also shows this wire splitting off and feeding the Heat(W), Cool(Y) and Fan(G) relay terminals as well???)

    Also, do I hook my existing Red wire to the "R" Terminal on the EIM? It is jumpered and doesn't appear to be 100% conducive to accepting another wire.

    FWIW, the Furnace is a Rheem Criterion ll with the 1028-928 control board.

    Thanks in advance for any guidance!

    First image is new Honeywell Vision pro wiring diagram.
    Second is of White-Rodgers Thermostat which is being replaced.

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    Last edited: Dec 14, 2009
  2. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    You would hook up a common to the thermostat so that you could run the thermostat off of the 24v transformer instead of a battery. Most thermostats give you the option of also installing a battery and just forgetting about the C terminal.

    Don't hook the C up to any of the other wires or else you're gonna create yourself a nice little dead short in the wiring.
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