Coleman Mach 3 thermostat retrofit

[GordonThree]

Hi gang,

I'm considering a retrofit for my Mach 3 from its existing manual controls to using an external thermostat, like a Ecobee or some such.

Ideally I want two relays, one for fan, one for compressor, so that I can run the AC in fan-only mode. There is little difference between high/low fan so I'll leave the manual controls on full-cold high-fan, when the external thermostat is being used.

Two trains of thought on this. First is "the right way", which is to replace the entire ceiling unit with one that has the junction box for an external thermostat. That seems excessively invasive, and eliminates the manual controls. It is also expensive.

The second train is jumper some 12v relays in across the existing switches that control the fan and compressor. I haven't taken my ceiling unit apart to see how accessible the wiring is, or if there's a safe place to secure the relays.

What does the hive mind think about either method?

[Joe417]

I went the route that RSL7201 went except I used a 40 Amp for the compressor and a 25 for the fan.

I didn't cut any of the Coleman wiring. Just unplugged existing wires from the manual controls and made jumpers to route them to the new relays. All were slide on spade lugs.

I put the fan relay on the low side only and still have a manually controlled high fan.
That worked great for us as we only need the high fan to cool it down when we first stop somewhere. Once cooled, we turn the manual control back to low cool and the thermostat takes control of both the fan and compressor.

Our camper is laminated polystyrene and I was able to make a flexible drill rod to make a path through the foam keeping the wiring in the ceiling and walls.

My cost, from ebay, was about $15 + a thermostat from Lowes.

I did the same to a neighbors Carrier unit, but had to removed his remote control hardware and had to run the thermostat wire across the ceiling using snap together wire hiding conduit that Lowes sells. It matched his ceiling well and isn't obtrusive.

As RSL7201 said, use the SSR-40DA or SSR-50DA for the compressor. The SSR-25DA is fine for the fan.

[ronday]

Just did this to the Coleman Mach 8 Cub in my truck camper. Removed the internal module and replaced it with a 9330A755 module to wire to the external thermostat which controls heating and cooling. Lots of info on u tube. Google this. Ron

[RLS7201]

I did the same project as you intend to do.
You'll get tired of the mechanical relays going thunk thunk.
I re-did my project with solid state relays.
Make sure and use the 50 amp relay for the compressor, as the back EMF, when the compressor shuts down, will blow a smaller relay.
I used two smaller relays for the two fan speeds.
I can't seem to get a link posted to the relays on Ebay
Look for "Single Phase Solid State Relay SSR-50DA 3-32VDC 50A/250V Output 24-380VAC"

Richard

[GordonThree]

So I'm not looking for the thermostat.
I'm looking for feedback on adding the thermostat interface.

I have the 100% manual ceiling unit, so there's nothing to wire a thermostat into.

[msb1766]

Got mine from Amazon also here is a link:
https://www.amazon.com/gp/product/B004RCOU9Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[JimJohnson]

Coleman Airxcel makes the thermostat you want. The trick may be getting the wiring from your roof unit over to the thermostat.

Here is the Amazon listing for the digital version:
Coleman Airxcel 8330-3862 T-Stat Wall Digital Heat/Cool
https://smile.amazon.com/gp/product/B01M8LFHT3/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

We have this thermostat and a Coleman Mach A/C unit. The wiring was factory, we upgraded thermostat from the factory provided analog unit as the digital version is more accurate and the wiring harness is identical between the two versions.