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    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #1

    Dec 23, 2008, 07:28 AM
    Replacing T874R/Q674L with RTH7600D 1006
    I am trying to replace my thermostat and need help.

    my old thermostat is a T874R with Q674L sub. The wiring diagram can be seen here.

    http://customer.honeywell.com/techli...0s/60-1152.pdf

    Page 9, Fig. 14.

    T is not used.

    All other wires are present (W2, G, R, X, Z, K, Y, W1)

    ---------------
    My new thermostat is RTH7600D. The installation instructions are here.

    http://customer.honeywell.com/techli.../69-2206ES.pdf

    ---------------

    I can not figure out the configuation that I need. Any help would be appreciated.

    -Greg
    dac122's Avatar
    dac122 Posts: 463, Reputation: 17
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    #2

    Dec 23, 2008, 10:21 AM

    Are you having trouble wiring it or configuring the new tstat? Please describe your system (HP, furnace, air handler, etc.)? Manufacturers and models would be helpful.

    Without knowing what you have its hard to tell you how to configure your tstat.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #3

    Dec 23, 2008, 10:22 AM
    Here are the directions for your old subbase/thermostat. Just transpose the wiring from the old as posted to the new unit.


    http://customer.honeywell.com/techli...0s/69-0272.pdf
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #4

    Dec 23, 2008, 10:32 AM

    It is a heat pump made by intertherm. I cannot access the model number right now. I might be able to get it when I get home.

    I am not sure about the wiring, My thoughts are

    old=new
    R=R
    Y=Y
    G=G
    X=C?
    Z=L?
    W1=B?
    K=E?
    W2=Aux?

    Am I close?
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #5

    Dec 23, 2008, 01:23 PM

    update:

    This is a revised list after a little more insight...

    old=new
    R=R
    Y=Y
    G=G
    X=C (common)
    Z=unused (LED for Service)
    W1=O
    K=unused (LED for Em. Heat)
    W2=Aux

    Jump E and Aux together.

    Is this correct?
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #6

    Dec 23, 2008, 01:28 PM

    Almost... W1-O? A heat pump will require either B or O for the reversing circuit (usually O). Connecting W1 to O will activate auxiliary heat when thermostat is set to cool. Post wire colors that correspond to old.
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #7

    Dec 23, 2008, 01:30 PM

    So, W1 should be B?
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #8

    Dec 23, 2008, 01:33 PM

    W1 should not be either O or B. Post wire colors that correspond to old.
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #9

    Dec 23, 2008, 01:37 PM

    R=Red
    Y=Yellow
    G=Green
    X=Black
    Z=Tan/Brown
    W1=White
    K=Orange
    W2=Blue
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #10

    Dec 23, 2008, 01:39 PM
    The reason I say that the W1 is B is because on the diagram it shows it between the Heat Changeover Valve and the rise/fall switches
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #11

    Dec 23, 2008, 01:45 PM

    While variations are possible, the orange wire is most commonly used for the reversing circuit (hence the "O" terminal designation). Does your new t-stat have an "O" terminal? It may be combined with "B", look closely...
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #12

    Dec 23, 2008, 01:48 PM

    It has an "O/B" designation.
    dac122's Avatar
    dac122 Posts: 463, Reputation: 17
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    #13

    Dec 23, 2008, 01:49 PM
    Quote Originally Posted by greoryg View Post
    update:

    This is a revised list after a little more insight...

    old=new
    R=R
    Y=Y
    G=G
    X=C (common)
    Z=unused (LED for Service)
    W1=O
    K=unused (LED for Em. Heat)
    W2=Aux

    Jump E and Aux together.

    Is this correct?
    After looking carefully at both manuals, this is the mapping I'd guess at. To be sure you can wire it up in stages: first just power, then add the fan, then your aux heat only, then your HP. If you can't figure the Hp immediately you'll have aux heat.
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #14

    Dec 23, 2008, 01:50 PM

    I would suggest you re-consult with hvac1000 as he has unlimited access to technical references that might reveal something unconventional about your arrangement.
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #15

    Dec 24, 2008, 05:16 PM


    These are pictures of the front panel in my unit.
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
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    #16

    Dec 24, 2008, 05:51 PM
    Quote Originally Posted by greoryg View Post
    These are pictures of the front panel in my unit.




    Attachments won't open.
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #18

    Dec 25, 2008, 05:48 AM
    Merry Christmas to you and yours.

    -Greg
    greoryg's Avatar
    greoryg Posts: 11, Reputation: 1
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    #19

    Jan 4, 2009, 08:56 AM

    Are the photos any help in solving the case?
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #20

    Jan 4, 2009, 10:23 AM
    Actually I do not see a case to solve. Tape off K and Z and then wire it according to the instructions in the new stat. Then make selections settings for your unit as in O or B? etc. The old subbase drawing shows what the old terminals were used for so just transpose them to the new thermostat.
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