Coleman Mach Air Conditioner Troubleshooting

[BR549]

Sorry...I'm not following the symptoms very well. Is the list below correct?

Fan Low = bad
Fan High = bad
Cool Low = good
Cool High = good
Cool Low Auto = bad
Cool High Auto = bad

That’s correct.

[BR549]

Since you have TWO A/C units you probably have TWO Thermostats. It is so easy to just take these off the wall and swap them and see whether the problem follows the thermostat or stays with the A/C unit. Make sure you take pictures of the wires going into the thermostats before moving them.

Yours is an interesting problem since the thermostat controls power to the fan and there isn't a separate wire for Fan High, Cool High, or Cool High Auto. It is the SAME wire for all three settings. So my bet is on the thermostat not energizing the fan wire in two of the three settings.

Would they still be interchangeable to diagnose since the bedroom is a Cool Only model?

[howson]

BR549


Do you have a multimeter and know how to use it? I'm out shopping w/the DW but when I get back to the camper I can do some baseline measurements if it will help.

[howson]

BR549 -- disregard post 18. I just tried to take some measurements and it's a lot harder than I anticipated. The leads I have with me won't work--a specialized lead (with super small and sharp probes) are required.

[howson]

...wouldn’t the problem likely be with the control board in the plenum?

I don't know. The failure mode doesn't make sense. The report that the issue is repeatable is befuddling.

What I did see (on my control box) is that there are two white wires going into the B- plug. These are the -12v returns (aka "ground"). Long shot, but I'd pull that connector and install a new end, recrimping to ensure it's good. I can't fully explain the rationale, but I can't make sense out of the failure reported. (Sorry!)




Swapping thermostats is an option, but the bedroom likely is a different model that does not have furnace (heat) capability.

If you're really up for a challenge, swap the control box between the air conditioners. That should answer the question if it's the box or not. I can't think of any other option at this point.

[BR549]

I don't know. The failure mode doesn't make sense. The report that the issue is repeatable is befuddling.

What I did see (on my control box) is that there are two white wires going into the B- plug. These are the -12v returns (aka "ground"). Long shot, but I'd pull that connector and install a new end, recrimping to ensure it's good. I can't fully explain the rationale, but I can't make sense out of the failure reported. (Sorry!)




Swapping thermostats is an option, but the bedroom likely is a different model that does not have furnace (heat) capability.

If you're really up for a challenge, swap the control box between the air conditioners. That should answer the question if it's the box or not. I can't think of any other option at this point.

Thank you for taking your time to look at the issue. It seems that if the fault was in the thermostat the fan would come on with Fan Hi and Low as it does with Cool Hi and Lo. I may try the swap before we leave for home.

Thanks again.

[pengle]

Would they still be interchangeable to diagnose since the bedroom is a Cool Only model?

You can still do the temporary swap using the bedroom (Cool Only) thermostat in placed of the living room (Cool and Furnace) thermostat. After the swap you won't plug in the WHITE wire anywhere since it provides the furnace power. You don't have to mount the thermostat. You'll just have it hanging there with all wires except the White one installed. Then run through all of your Fan settings and see which settings the fan will come on with.

As you can tell by all the comments your failure mode doesn't make sense to most of us who know how it SHOULD work or SHOULD fail. The failure mode doesn't make sense electrically so that's why I think something inside the circuit board of the thermostat has failed - we can't see all of those connections.

[BR549]

Thanks, all. Since it’s still in the 24 month warranty from Coleman Hach, I’ve decided to forego swapping thermostats and look for a service center where I can have it checked. If I can get it into a shop, I’ll let you know what they find.

[BR549]

The result is in.
Thermostat replaced under warranty.