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Dave_H_M's avatar
Dave_H_M
Explorer II
Sep 24, 2019

Wiring a ColemanMach Thermostat?

I have to replace my Hunter. It will not remember the cold setting it has been set on.

I have an RV Comfort.HC Coleman-Mach Thermostat. Colors of the wires coming out the back are: Yellow, Green,Blue,White,Red, and Grey

Two bundles of wires lead to the opening in the fifth wheel.

One bundle has a red and white in it

The other bundle has a blue, green, white, and red wire in it.

I bought this TStat a long time ago based on a post here and have since misplaced/lost instructions. After finding a loose wire,I really thought I would not need it but the Hunter went south again today.

i have went nutso on the YOUTube site this eve.

I would be thankful if someone could tell me what to wire nut together or point me in the direction of where to get that info on the internet. It is gona be at least a week and a half until I am in an area where Mobile techs will be available as a last resort.

Thanks in advance.

I found out the function of the TStat wires by color:

green high fan
grey low fan
yellow compressor
red 12V DC pos
Blue 12V DC neg
white heat
  • Dave_H_M's avatar
    Dave_H_M
    Explorer II
    Oct 07, 2019
    Well won't go into the reasons, but we did not make the get away and the camper is back in the barn.

    I needed to get this Tstat install sorted out. So I dug thru some old notes and some head scratching looking at the previous wiring job.

    Soooo, on this Laredo the four wires in the bundle coming from the air conditioner worked out to be.

    Green - low fan
    red - compressor
    white - high fan
    Blue - 12V - (ground)

    The white and red coming from the heater were

    Red - 12V +
    white - heat

    So hooked them up accordingly and all is well.

    Thanks all.
  • Dave_H_M's avatar
    Dave_H_M
    Explorer II
    Sep 24, 2019
    On edit: You reference Yellow, Green, Blue, White, Red, and Gray going into the the existing t-stat. However, you say the bundles have red/white and blue/green/white/red. There's a yellow missing somewhere, which I suspect is an oversight in the second bundle...

    No oversight. The yellow is not there. i am suspecting that the bundle that was run from the ac to the stat was not "standard". So i don't know which wire is substituted for the yellow.

    And labeling on the mach is not the same as the hunter. So at this point I am throwing in the towel and looking for a mobile tech when I get to the east coast. :S
  • ScottG's avatar
    ScottG
    Nomad
    Sep 24, 2019
    happy2rv wrote:
    ScottG wrote:
    Oddly, my Mach Digital stat does not use the blue wire although it is dangling loosely inside the wall behind it.

    Interesting. You appear to have a black wire in the photo. The blue wire is usually 12V- / battery negative. I'm not sure if your black is in place of the blue or not. If it is its hard to say why... RV manufacturers seem to love doing things in the most interesting ways ;).

    On edit: After studying your photo, yours seems to have several "non-standard" color variations. It looks like your black wire is the furnace and your white wire is battery negative. The white battery negative is somewhat of an RV standard, but not standard for the AC.

    For anything that's wired standard, it should be:
    R - Red +12V
    B - Blue 12V- i.e. 12V ground
    GH - Green High Fan control
    GL - Gray Low Fan Control
    W - White Furnace control

    These labels should be on both thermostats. Wire colors ideally should match, but like I said, the RV industry likes to keep it interesting. Move wires between terminals of the same labels on both t-stats and it should be good.


    Good post - thanks!
  • happy2rv's avatar
    happy2rv
    Explorer
    Sep 24, 2019
    ScottG wrote:
    Oddly, my Mach Digital stat does not use the blue wire although it is dangling loosely inside the wall behind it.

    Interesting. You appear to have a black wire in the photo. The blue wire is usually 12V- / battery negative. I'm not sure if your black is in place of the blue or not. If it is its hard to say why... RV manufacturers seem to love doing things in the most interesting ways ;).

    On edit: After studying your photo, yours seems to have several "non-standard" color variations. It looks like your black wire is the furnace and your white wire is battery negative. The white battery negative is somewhat of an RV standard, but not standard for the AC.

    For anything that's wired standard, it should be:
    R - Red +12V
    B - Blue 12V- i.e. 12V ground
    GH - Green High Fan control
    GL - Gray Low Fan Control
    W - White Furnace control
    Y - Yellow Compressor control (cooling)

    These labels should be on both thermostats. Wire colors ideally should match, but like I said, the RV industry likes to keep it interesting. Move wires between terminals of the same labels on both t-stats and it should be good.
  • ScottG's avatar
    ScottG
    Nomad
    Sep 24, 2019
    Oddly, my Mach Digital stat does not use the blue wire although it is dangling loosely inside the wall behind it.
  • happy2rv's avatar
    happy2rv
    Explorer
    Sep 24, 2019
    One bundle, almost certainly the red and white, should be the furnace. These are standard colors. The other should be the AC. A quick Google search for Coleman Mach Wiring Diagram shows lots of wiring diagrams. The t-stat should have labels for the blue, green, gray, and yellow wires to the AC. These are also standard colors. Not sure about the white wire in this bundle. How is it connected to the existing t-stat?

    Take pictures before disconnecting, if you haven't already.

    On edit: You reference Yellow, Green, Blue, White, Red, and Gray going into the the existing t-stat. However, you say the bundles have red/white and blue/green/white/red. There's a yellow missing somewhere, which I suspect is an oversight in the second bundle...

    The t-stat should have either similarly colored wires or labeled terminals. The labels may be molded into the plastic and hard to read. On the top of ScottG's photo above, it looks like the labels are silk screened in white behind the wires.
  • wnjj's avatar
    wnjj
    Explorer II
    Sep 24, 2019
    Dave H M wrote:
    Two bundles of wires lead to the opening in the fifth wheel.

    One bundle has a red and white in it

    The other bundle has a blue, green, white, and red wire in it.

    Are the wires still connected to the existing thermostat? If so, please note the connections as the wiring in your RV doesn't necessarily follow a standard. Then you can match old thermostat for new.

    If they're already disconnected, you may have to pull the A/C cover to see where they go or use trial and error.

    My (slightly educated) guess:
    The red & white bundle are +12 (red) and heat (white) and head to/from the heater. Shorting those together should make the heater start.

    The other bundle heads to/from the A/C and will consist of a ground (usually blue), cool (usually yellow but you don't have one), fan low (usually gray, again you don't have) and fan high (usually green).

    As you can see in this outback owner's post, the trailer wire colors have nothing to do with the thermostat standard colors.
  • ScottG's avatar
    ScottG
    Nomad
    Sep 24, 2019
    Not sure if this helps but I took a pic of the wire connections on my Coleman Mach thermostat so I could move the stat from its current (idotic) location to a better one.

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