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Old 07-16-2021, 07:12 AM   #1
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Coleman Mach 8 Heat Pump question

About a month ago I needed to use my heat pumps to take the edge off of morning cool air. I usually use the front and mid to keep the noise in the bedroom down. My middle unit clicked (thermostat) and started for about one second then shut down. It would not restart. My first instict was the capacitors, so I replaced both. I thought it was odd that the old capacitors tested to spec but I checked all connections. Interestingly, it turned hot so while I tested the AC side, I never did revisit the heat pump side.

This morning it turned cool (All 3 AC's performed admirably during a month of 105 plus weather) so I fired up the center HP and it exhibited the same symptoms. Acted like it would start, then shut down and not start at all.

While I don't require all three HP's, it bugs me something doesn't work. Anyone have any suggestions on what the cause may be?

Thank you.
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Old 07-16-2021, 08:18 AM   #2
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Are the three units connected together thru a central controller? If so it could be the controller telling the units not to fight each other (2 cooling, one heating).

Will the unit start and run OK in cooling mode? If so it rules out capacitor side issues - itís now a reversing valve issue. Reversing valve is normally controlled by the thermostat.
But it doesnít explain the 1 second shut-down. That sounds more like an electrical issue.

There is no good way to load test a capacitor. It can read to be in spec with a meter, but a meter canít load a capacitor like a motor load can.

I would carefully recheck all wiring for the capacitors and compressor/fan motors. These units are notorious for poor crimp connections. Typical signs of poor connections are darkened/discolored wire insulation and stiff wiring. Tarnished and/or green corroded connectors are also signs of bad wiring terminations.

Determine if your unit uses a PTC start type or potential relay type of compressor start kit. IF it is a potential relay type of start kit where there would be a black plastic capacitor used to start the compressor, there should be a 10k ohm resister across the top of the cap. They donít usually come this way from the factory, you have to add it.
There is a purpose for this resistor, but too detailed to go into using this venue.
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Old 07-16-2021, 11:11 PM   #3
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My unit has a separate control for each unit. AC (cooling) works fine. I am leaning toward the reversing valve or relay at this point. Will follow through investigating your recommendations too.
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Old 07-17-2021, 05:18 AM   #4
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On our 2014 Phaeton , there are only 2 heat pumps , front and rear the middle one when turned on will automatically get to Gas furnace.
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Old 07-17-2021, 05:19 AM   #5
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A reversing valve getting stuck isnít unheard of, but not real common in my experience.

I would be checking to make sure the reversing valve coil is being properly held in place. Followed by checking the control wire for that coil going all the way back to the thermostat (are the thermostat wire connector screws at the thermostat all tight?). Finally, a check of the reversing valve coil itself.

My memory is kind of fuzzy on this, but I believe most reversing valves - when the coil isnít powered - will be in heat mode, and it takes power to make them switch to cooling mode. Not sure for a motorhome or RV what coil voltage is used, 12VDC or 24VAC or 120VAC.
So saying that, it seems weird that the issue your having is with heating since cooling seems to work.
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Old 07-17-2021, 06:07 AM   #6
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^^^^+1 If its cooling fine, then you have either a faulty reversing solenoid valve or a thermostat. The solenoid valve will be 120vac and energized in the heat mode of your thermostat. If you desire to get up on the roof and remove the cover, then I or others here on the forum can help with diagnosing.
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Old 07-17-2021, 06:16 AM   #7
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Attached is a Mach 8 service manual. Take it for what it is. Airxcel does a terrible job managing documents.
Attached Files
File Type: pdf Coleman Mach 8.pdf (700.2 KB, 20 views)
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Old 07-17-2021, 10:24 PM   #8
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Thanks all. I did find the manual and read it. Kind of simplistic when it comes to troubleshooting.

I will eventually get up on the roof, but am going to wait for moderate Temps. Then I may ask for help. First, though, I do want to inspect all connections and wiring.
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Old 07-27-2021, 09:17 PM   #9
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I just went through this. Turned out to be the connection on the controller, which is under the evaporator cover in the front of the unit. The white/black call for heat wire from the thermostat is changed to white in the Tiffin harness. The white wire spade connector had intermittent continuity.
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Old 07-27-2021, 10:50 PM   #10
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Thanks. Will start there when I get up on the roof next week. Which is the evaporator cover. I have pulled the cover where the capacitors are located, do I just follow those wires?
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Old 07-28-2021, 08:36 AM   #11
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Never mind my last question....you did say "on the front of the unit" which I missed. Thanks again.
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Old 07-28-2021, 11:41 AM   #12
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I figured I had some kind of bad connection because it worked when I bought the coach and then didn't when I needed it. I looked at it and did a few continuity checks back to the thermostat after which it started. Next day, wouldn't run. I went on the roof uncovered the wires and turned it on and then started checking each connection by gently moving the spade lugs and wires, starting with the white call for heat. Bingo! New spade lug and using tie wraps to prevent the side pull on the wires as installed should hopefully resolve the issue permanently.


The wiring isn't exactly neat and I spent some time tidying things up last time I had it open. Plan to do the same next year to the other two when I do my annual cleaning.
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