12VDC Heat Pump Thermostat to control Coleman Mach 3 AC and Gas Furnace

[kuba122]

Yeah ... ac and dc share a common ground. I found that out when one of my GFCI outlets popped and took out my solar controller. It was an expensive lesson. I have since isolated the solar controller from the common ground.

[Hotrock59]

No need to run a separate wire to power center, simply attach blue wire to to new controller metal housing as it is grounded, ac and dc circuits share ground so it makes this mod much easier, determine which of the the 2 wires to wall mounted t-stat is 12 vdc+, attach it to red wire going to new t-stat and new controller. Use the other wire to attach to gas heat terminal on new t-stat.

[kuba122]

Remove the AC Cover and take out all of the control knobs, disconnect the power (make sure breaker is off or the RV is not plugged in!!) Figure out a way to run a new 6 conductor cable to the existing thermostat location and prepare the route. (You can see the speaker I dropped and I also took down a light fixture in the bathroom I drilled 2 small holes and used a wiremold piece to cover the cable path between the ceiling and the wall in the bathroom .... I'll be providing more pictures.

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Remove the power Center and run a blue wire from the AC to the power center. I went through the speaker hole, to the area behind the microwave (had to remove the microwave), then down to the power center. Wasn't easy, but I was able to get the cable down there, inside the wall. Completely hidden.

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More to come .....

[kuba122]

The principals of this mod are easily transferable to other models of AC/Furnace Combinations.

This is Stage 1 of a 2 Stage Mod. This first stage provides simple control of AC and furnace.

Parts Required:

Control Board - Coleman 9330C755
Electric Heat Element - Coleman 9233A4551
Thermostat 12VDC - NEW Coleman 8530A3451

Features and benefits of this configuration:

AC Blower controlled like your home system, when set to auto fan mode it will turn on and off as AC is running or Not running.

The Thermostat runs on 12VDC so the Gas Furnace does not require a seperate controller and will run without 110V present.

If 110V is present electric heat will run, as long as it can keep up with heating and will revert to gas furnace if electric heating cannot keep up.

More accurate AC Heat control than the original provides.

Description of Modification

Cable will need to be run between Existing Thermostat and AC system. Blue wire will need to be run from either the Thermostat to the power center or from the AC unit to the power center. This blue wire will be used to unify the 12VDC ground throughout the system.

Remove cover from AC unit. Remove knobs from AC Unit cover and remove wiring. Connect wires in accordance with the control board instructions and attached schematic. Install the heat element and control board inside of the Mach 3 AC Unit.

Remove Existing Furnace Thermostat connect new thermostat wires to cable wires and Mount New Thermostat.

Connect blue wire to 12VDC ground in power center and put everything back together.

Documenting this mod will take some time .... I will provide pictures as we move through the nuts and bolts. Attached here is the schematic in picture form.

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