Coleman Mach Air Conditioner Troubleshooting

[hduring]

Spending the day in western Kansas, besides the wind it is also 92 degrees outside. Anyways, when we arrived at our CG, the RV interior was a nice, bug destroying 93 degrees. Turned on the main thermostat to Auto Hi Cool and set temp to 78 degrees. No matter what we did on that Coleman AC and thermostat, the temp in the main living area would drop only a couple degrees. Turned on Maxxair fan in kitchen thinking it would push hot air out, no help (don’t completely understand that fan). Note that our bedroom was getting cooler the entire time. The thermostat in the bedroom showed a reasonable 82 degrees even though it was off. Tried closing the vents in bedroom AC, then main living area AC vent, one at a time, but no change. We then turned on bedroom Coleman Mach AC using bedroom thermostat and now finally the RV is cooling off. Question is, why would bedroom AC have an affect on main area temps? Note that cold air was coming from main area ceiling vents the entire time but not really strong like it seems to be doing now. We thought the bedroom AC was only good for the bedroom? Right now, with both AC’s running, the RV is cooling off nicely. TIA for any inputs/advice.

[Skiba]

Is your bedroom AC ducted? Our bedroom ac is not ducted and when it is hot as it is now in SW TX we need to keep the bedroom door open and use a fan to blow the cool air to the living area

[Country Campers]

Both AC's are ducted. You may want to drop the interior cover of the rear AC to see if the chambers are split and sealed properly. The rear chamber will be the cold air out and the front chamber wlll be cabin air in if they are leaking between the two you will not get good air flow from the ceiling ducts. If the AC has the foam block air flow installed it may be installed incorrectly also causing poor air flow.

Brian

[howson]

hduring -- the video Chad and Tara from Changing Lanes put together should help with understanding what you can check yourself.

[Jlawles2]

I have the same issue with our 303. I've tried closing the front ducts closing the door, etc. What we found works best is to set the rear to Lo or Hi Cool (not auto) open the bedroom door, and then set the bedroom AC to Hi Cool and about 2 degrees cooler than the rear AC and they cycle about the same then. Note that in the bedroom the dump vents can blow directly on the thermostat and cause it to early cycle. Because of this, I close both dumps and one of the duct vents (forces more air into the racetrack).

[hduring]

I have the same issue with our 303. I've tried closing the front ducts closing the door, etc. What we found works best is to set the rear to Lo or Hi Cool (not auto) open the bedroom door, and then set the bedroom AC to Hi Cool and about 2 degrees cooler than the rear AC and they cycle about the same then. Note that in the bedroom the dump vents can blow directly on the thermostat and cause it to early cycle. Because of this, I close both dumps and one of the duct vents (forces more air into the racetrack).

Jlawles2 Meanwhile, we are someplace in Tennessee, and we have the two ACs cooling the RV nicely. Joseph, a couple questions: what are the dump vents, are they the AC built in vents? Sometimes at night, the bedroom AC kicks on for less than 30 seconds and then turns off, is that early cycle?

We’ll try your temp / thermostat settings and see what happens.

[Jlawles2]

hduring The dump vents are the slider openings on the front and rear of the ceiling facia.

[BR549]

Both Coleman-Mach units have been working until today. When we arrived at our CG, we ran the living room unit to cool the trailer. It cycled off, but later when it came on again, we could hear the unit hum but the fan doesn’t come on when set to Hi or Lo Auto. The fan doesn’t come on when set to Fan, but does come on when the thermostat is set to Hi or Low Cool (just not Auto).

Any thoughts on why the fan would run on Hi or Lo Cool but not on Fan or Cool Auto? Thermostat issue or AC issue?

[howson]

Both Coleman-Mach units have been working until today. When we arrived at our CG, we ran the living room unit to cool the trailer. It cycled off, but later when it came on again, we could hear the unit hum but the fan doesn’t come on when set to Hi or Lo Auto. The fan doesn’t come on when set to Fan, but does come on when the thermostat is set to Hi or Low Cool (just not Auto).

Any thoughts on why the fan would run on Hi or Lo Cool but not on Fan or Cool Auto? Thermostat issue or AC issue?

Control box in the plenum? (Remove the filters and look at the connections.)

[BR549]

Control box in the plenum? (Remove the filters and look at the connections.)

Nothing obvious in the connections or wiring. Everything seems to be in place.

[howson]

Nothing obvious in the connections or wiring. Everything seems to be in place.

What prompted that thought was 50ST8R had a similar problem at the '22 National Rally. Neil, Brian and myself were over looking at the issue and just by slightly wiggling the wires on the control box the fan kicked on and off. If I remember right all we had to do was resecure the wires.

There is a way to move the fan control wires on the control box to see if it's the box itself (all the control box does is act like a relay). Examine the wiring closely and the designations and I think you'll see what I'm referencing (GH and GL).



CAUTION: YOUR WIRING MAY BE DIFFERENT FROM THE EXAMPLE SHOWN--VERIFY BEFORE SWAPPING ANYTHING!



Another possibility is the thermostat, or wiring at the thermostat. Since the fan appears to work in other modes it (and the start/run capacitors) should be fine--those parts don't care about the specific mode.

Finally, the symptom described--was it seen just once or is the problem repeatable no matter how long between attempts? (Fan and/or capacitor could be intermittent.)

Howard

[Scott'n'Wendy]

Both Coleman-Mach units have been working until today. When we arrived at our CG, we ran the living room unit to cool the trailer. It cycled off, but later when it came on again, we could hear the unit hum but the fan doesn’t come on when set to Hi or Lo Auto. The fan doesn’t come on when set to Fan, but does come on when the thermostat is set to Hi or Low Cool (just not Auto).

Any thoughts on why the fan would run on Hi or Lo Cool but not on Fan or Cool Auto? Thermostat issue or AC issue?

The exact same thing happened with our AC, and what Howard suggests is what fixed it. Before looking at the control box in the plenum I removed the t-stat and with a meter verified that the signal is being sent. It was...so....
I went to the plenum and the wiring looked fine. But I removed and reinstalled each one to verify a good connection anyway. After which it works fine. I have to think that one of the connections, while looking good, was in fact a poor connection.
*****Actually I didn't remove ALL the wires. One was so darn snug I couldn't pull it off by hand so I used needle nose pliers and just wiggled it for a bit to make sure it had a clean connection. It was taking SOOO much force to remove that I figured I would damage the board trying to pull any harder.*****

[BR549]

There are three wire connections to the board along with the large bundle. Pulled and replaced, but no change. It’s not intermittent. No fan on Fan or Auto settings.

looking at the operation chart for the AIRXCEL thermostat, it looks like the the gray and green wires are energized for Fan, Cool, and Auto. So if the fan works on Cool, then wouldn’t the problem likely be with the control board in the plenum?

[howson]

There are three wire connections to the board along with the large bundle. Pulled and replaced, but no change. It’s not intermittent. No fan on Fan or Auto settings.

looking at the operation chart for the AIRXCEL thermostat, it looks like the the gray and green wires are energized for Fan, Cool, and Auto. So if the fan works on Cool, then wouldn’t the problem likely be with the control board in the plenum?

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

[pengle]

Both Coleman-Mach units have been working until today. When we arrived at our CG, we ran the living room unit to cool the trailer. It cycled off, but later when it came on again, we could hear the unit hum but the fan doesn’t come on when set to Hi or Lo Auto. The fan doesn’t come on when set to Fan, but does come on when the thermostat is set to Hi or Low Cool (just not Auto).

Any thoughts on why the fan would run on Hi or Lo Cool but not on Fan or Cool Auto? Thermostat issue or AC issue?

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.