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Old 08-08-2021, 04:48 PM   #1
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Roof A/Cs cut off and don't restart

Greetings and looking for ideas. We have 3 rooftop Colman ACs on our 40ft 2011 Winnebago Journey, one an original "Polar Mach" and 2 replacement "Mach 8+” units.

Back when all 3 were Polar Machs, we had occasional issues with the front 2 trying to start and cutting off shortly thereafter at compressor engagement or within a few minutes of compressor engagement. Sometimes they'd reset themselves and start again successfully and sometimes they'd stay off, requiring us to reset the thermostat before they would try again.

As we've worked to diagnose this intermittent issue over the years, our extended warranty has replaced both units AND then their control boards, thus the upgrade to 2 Mach 8+s. We also replaced the thermostat, twice. Here we are having the problem again and finally realizing it only happens when outside temps are over 90. Interestingly enough, the rear still-original AC has never had this issue and still works like a champ all the time. Also, we've never noticed any issues with the heat pump mode on any of them.

Anyhow, if anyone has any thoughts of what else we can look at, please chime in! It is one of the few mysteries we haven't solved on this rig. We are okay with the ACs stopping and restarting themselves, but refusing to restart without system reset (turn ACs off at thermostat and then back on) is a hassle, especially if we aren't home to do it.
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Old 08-08-2021, 05:18 PM   #2
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Roof ACs cut off and don't restart

One question to start if you use only one of the front units will it work fine?
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Old 08-08-2021, 05:28 PM   #3
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One question to start if you use only one of the front units will it work fine?
Nope. Using the 120v breaker we isolated them from each other (they are on separate lines of our 50a power) and this issue still happens. They also aren't being "shed". The 2 ACs ARE on the same AC zone, though they are on a staggered start cycle if they are both on. The" always works" AC is on a zone by itself.
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Old 08-09-2021, 08:13 AM   #4
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Ok I do not have 3 ac so some one else can help but I don’t think they should be on the same zone.

The units have dip switch’s to determine the zone then you can reset the thermostat to see 3 zones not just 2
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Old 08-09-2021, 09:42 AM   #5
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Only speculation on my part, but the fact the issue only happens when outside temps exceed 90* seems to be a significant clue.


Both units work together when in heat pump mode which means it is not an overload problem on the circuits as you already determined. The only variable that changes is the outside temperature. I know nothing about the workings of the units, but I think this would be a good line to follow. Something about high heat on the units prevents them from operation correctly. I would guess there is some type of thermal cut-off switch that protects the compressor, and maybe that is not protected from high ambient temperatures.
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Old 08-09-2021, 01:32 PM   #6
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Since they only quit when it's very hot outside, I think that the thermal breakers may just be doing what they are intended to do. I have operated my AC's in 118 degree temps when stationary, but the thermal breakers will trip when driving. Must be some kind of airflow issue.
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Old 08-09-2021, 02:07 PM   #7
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You are going to just bite the bullet and add 2 soft starts to problem a/c.. yes close to 800 with tax and shipping.. maybe a little cheaper.. but that's what I would do.. rv tech can come out and put on.. but labor is extra.. still small price to pay for comfort in 90+ weather.. good luck and let us know what you did and maybe better members then me will help you
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Old 08-09-2021, 02:10 PM   #8
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Oh.. to save a buck.. you could just try one soft start.. see if that helps.. I would test amp draw on each one and install on one that pulls most amps..
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Old 08-09-2021, 04:41 PM   #9
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Thanks everyone for your ideas. We welcome more if other thoughts pop up. We are in 70 degree temps for the next month and so of course all is running perfectly, but we'll head into higher temps at the end of the month if there are any test cases (former SW programmers!) you can think of for us to try. Husband is going to try running just the fan for a few minutes before engaging the AC at the thermostat to see if that helps. For those thinking about this issue, remember AC #1 (rear) has always been happy as a clam (always wonder where this saying came from?). ACs #2 (middle) & #3 (front) are the problem children, #3 maybe more often than #2. Coleman is going to get a call as well, but often we find the experiences of other owners help solve a problem or at least narrow the scope.
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Old 08-09-2021, 04:53 PM   #10
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I would really try getting them on different zones…has anyone ever had 2 units on the same zone?

I know you pulled the 120 but the thermostat runs on 12v along with the controller board on the ac unit.

Maybe just unplug the phone cable to one of them and see if there is an issue.
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Old 08-09-2021, 11:19 PM   #11
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Can you tell us what Coleman T-stat you are using? I agree with Biljol, I am guessing a control problem. You say you have had the issue with the older units, then replaced with Mach 8's, and still have the same problem.
Can you clarify both ac units are controlled from one t-stat? If so, I believe that is why your having the issue. That's a lot to ask for one stat to handle. The stat is probably hanging on by a thread in the voltage department and as soon as it see's the higher ambient temps, bam..it drops.The Mach 8's require 7 or 8, 20 ga.wires iirc, from the stat to the control board. This would mean a whole bunch of splicing going on behind the t-stat base.

I run 3 Mach 8 15k's in our coach, but each has its own t-stat.( RVComfort.HP) Never had a dropout in very hot temps, driving or not.


Thats a very unique problem your having and one I have never heard of with the Mach 8"s. Hopefully you can get it resolved.
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Old 08-10-2021, 01:11 PM   #12
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Can you tell us what Coleman T-stat you are using? I agree with Biljol, I am guessing a control problem. You say you have had the issue with the older units, then replaced with Mach 8's, and still have the same problem.
Can you clarify both ac units are controlled from one t-stat? If so, I believe that is why your having the issue. That's a lot to ask for one stat to handle. The stat is probably hanging on by a thread in the voltage department and as soon as it see's the higher ambient temps, bam..it drops.The Mach 8's require 7 or 8, 20 ga.wires iirc, from the stat to the control board. This would mean a whole bunch of splicing going on behind the t-stat base.

I run 3 Mach 8 15k's in our coach, but each has its own t-stat.( RVComfort.HP) Never had a dropout in very hot temps, driving or not.


Thats a very unique problem your having and one I have never heard of with the Mach 8"s. Hopefully you can get it resolved.
Our thermostat is an RVComfort.ZC. We only have the one thermostat (replaced twice with same model) with two sensors, one for each zone. Problem zone has 2 ACs it controls and it staggers their startup if we turn both ACs on. Your thoughts on the possible wiring splicing to the 2-AC zone are interesting. Not sure I understand how the heat would be a factor...
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Old 08-10-2021, 02:56 PM   #13
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Ahhh, you are in a Winnebago. Can I assume you have the 8430a331 t-stat? Its the only one that I see is a multi-zone? I tried to upload the pdf but the file was too large.
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Old 08-10-2021, 08:25 PM   #14
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Ahhh, you are in a Winnebago. Can I assume you have the 8430a331 t-stat? Its the only one that I see is a multi-zone? I tried to upload the pdf but the file was too large.
Yes, this is the thermostat we have
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