A/C furnace not working.

[imenzies76]

Hi again, this past weekend i took the trailer out for the weekend. Hooked up the generator for power and to my suprise, the furnace nor the A/C was working. I've checked several items such as the breaker, fuses, thermostat fuse. Still not working. I called the dealer today and they told me there's a fuse up there(ac unit) which controls the whole unit and sends power to the thermostat.
I can't find this fuse to check it.
2017 cougar 33mls with coleman mach t stat and airxcel ac unit.
Any ideas?
Thanks

[imenzies76]

So I've checked every fuse that i can find. Is there any inline fuses that are hidden?
Not sure where to go from here.

[LHaven]

Just for giggles, make sure your battery disconnect switch is in the on position. A lot of needless heartbreak in that "feature"... though it shouldn't affect the A/C, so I'm guessing that's not it.

In the 2019s, at least, there is a "gateway" logic unit suspended smack in the middle of the empty space in the A/C intake area. It mediates the A/C. furnace, and thermostat. If any part of it is user-serviceable, it escaped me. On mine, the thing is a completely featureless white box, with the label on the top side (had to use my smartphone to photograph it) and a bunch of cables coming out one side. If you have one of these, it's a likely culprit given your combined symptoms.

[imenzies76]

So i have power 12vdc to the control box at the furnace. I was talking to a tech today and he suggested jumping the 2 blue furnace wires to eleminate the t stat. However, of course there isn't 2 blue wires to be found. I took a picture of the control box, can anyone tell me which wires to jump to dire the furnace up?

[LHaven]

An educated guess would be two of the five in the socket in the upper left-hand side (when the photo is right-side up). But without mfr/model for either the board or the furnace, I haven't been able to find this board pictured elsewhere. Maybe one of the pro techs on the forum would recognize it offhand, but I can't.

[MarkEHansen]

Do you have a normal thermostat? Take it off the wall and see what are the wire colors that connect to it.

[imenzies76]

Yes it's a coleman mach analog t stat. Yes the wires run back there but there is only 1 blue wire. The furnace is an atwood amf series.

[MarkEHansen]

What I meant was do you see the same wires at the control board as at the thermostat? Those are probably the thermostat wires.

[chuckster57]

Originally Posted by imenzies76

Yes it's a coleman mach analog t stat. Yes the wires run back there but there is only 1 blue wire. The furnace is an atwood amf series.

There should be 4 wires coming to the furnace:

12V positive
12V negative
“Heat” signal wire from thermostat
“Heat” signal wire from furnace to thermostat.

Simple explanation: you turn up the thermostat, the circuit is completed in the “signal” circuit and the furnace starts. It will go through it’s cycle and once the set temp is reached, the “Heat” signal is no longer complete and the control board puts the furnace in “cool down” mode.

Tech just wanted to have you “complete” the signal circuit and force the furnace to start it’s cycle. We do this regularly as part of our “bench test”. Your furnace will have a wiring diagram to help identify the wires. You just need 12V and a “completed” signal circuit to test.

[imenzies76]

Yes Chuckster, thats what I'm trying to do. Will these wires be on the control board? Can you tell from the pic what wires these are? Because I can't.

[chuckster57]

Hard to see, maybe the white insulation with the blue and brown/red wire? There should be some printing on the board that will say “therm” or something like that. The schematic will tell you for sure.

[LHaven]

Think of it this way. The thermostat takes four wires. They're signal wires, not high-current wires. They would be bundled in a single cable and the design engineer would group them into a single plug into the board. Where are there four smaller-gauge wires bundled in a single cable and plugged into a single connector on this card? Upper left hand corner, and it's the only place.

(Since my original posting, I figured out that the "fifth" wire is actually an optical illusion -- it's a jumper on the plug itself and doesn't really come out of the cable.)