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Old 05-19-2018, 06:42 PM   #1
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Duo-Therm 620526.321 Problem

I've had this problem with the main AC for a while now but since it's warming up it probably needs my attention since I'll be heading out to Orlando in a few weeks.

My main AC, the Duo0Therm 620526.321, blows hot air on the inside and strangely enough cool air to the outside. I understand that hot days deserve to cool down a bit, but I'd rather it cool the inside of my RV instead of the outside.

I'm not sure why I crawled on top of the roof to investigate, but I did anyway. I took the top off and whatever else I could safely remove to see as much as I could. Once again, not sure what I was expecting to find unless there was a neon sign pointing to the problem, which I didn't see one.

While I would give up on this unit and get my penny jar out, sell my plasma, have a yard sale, bake sale and whatever else I could do to buy a new AC/Heat pump unit if I didn't feel any cool air at all, but I do, albeit it's on the outside, and it is very cool indeed.

I did a search on the irv2 site and found a few similar problems, one gentleman said his unit was in heat pump mode. I do have it set to AC. I even turned on the heat pump and it actually blew even more heat into the unit, I was hoping to trick it to think I wanted heat and it give me AC. Nope.

The one thread in particular mentioned a reversing valve which I have no idea what that is; I didn't notice neon lights pointing to the reversing valve.

I'm somewhat handy and do enjoy tackling such projects since I only have so much plasma and one penny jar.

Is there anyone out there who has had this same problem and can clue me in on the location of the reversing valve. I saw a pair of solenoids which I know better to not touch, but nothing that resembles a reversing valve, I did see a picture of one, so if it's hidden under something I didn't take apart then I have no idea where it's located.

In case I have to replace the unit, what's an adequate replacement that would work in conjunction with my bedroom AC unit?

Thanks so much in advance, sorry for being a bit wordy.
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Old 05-19-2018, 08:04 PM   #2
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It probably is the reversing solenoid. To find it you should be looking for copper tubing that comes out of the compressor, evaporator and condenser, it should go through a device that has two wires coming out of it. They should be black wires. Here is a post from 007 with a link the the manual.

The issue could be the relay on the control board that runs the solenoid, the wiring, the solenoid coil or the solenoid itself. The first three are electrical and relatively easily repairable, the fourth will require opening the refrigerant system and replacing the solenoid, Dometic considers it non-repairable and may not sell you the part even if you could find an A/C person to do it.
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Old 05-20-2018, 08:56 AM   #3
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I had a reversing valve solonoid replaced a few months ago. Here is a picture. Its that shiny square surrounded by all the dusty items.

The 2 wires attach to a circuit board. Working with those wires will have you close to 2 high powered capacitors.

Make sure you discharge those bad boys. They bite!
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Old 05-20-2018, 09:09 PM   #4
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Not sure why mine looks not much like yours, maybe that''s my problem I lost my reversing valve. Just kidding.

Not sure exactly what's going on with my system. I'm trying to get hold of a mobile RV Tech to come out and look over my system. My bedroom AC is ice cold but the main area is the exact opposite.

Attached is a picture of mine.

Thanks so much
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Old 05-21-2018, 01:06 PM   #5
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Now this makes sense. I just double-checked the number 620526.321 and it is an air conditioner not a heat pump! You don't have a reversing valve! It's very weird that you feel significantly cooler air on the exhaust of the outside of the unit.

However, troubleshooting is simpler with an A/C. The issue could be that the compressor does not turn on, the starting circuit or start or run caps could be bad, the compressor is frozen or the system has lost its refrigerant charge. The first few are pretty easy to fix but the last two are difficult.

Here's how I'd go about troubleshooting (I've done all of this, I'm not an A/C expert, just a jack of all trades, so those of you who are experts please treat me gently while you correct me):

Do you have any kind of energy management system (EMS) on your coach? If so, you can run your generator so you get the current display and try to run the bad unit. Compare the bad unit to the good unit to get an idea of what the display does with both.

If the compressor is turning on you'll see a significant increase in current, something like 10 to 17A, and you'll hear it turning on. If it does not turn on you can try replacing the control board. When I had this happen a relay had gone bad, I replaced it and resolved the issue.

If the compressor draws tons of current (over 30A) for a short period of time and does not turn on, also you may hear a humming sound as it tries to start. One of several things could be wrong. One, the starting circuit, which could be a relay or PTC, could be bad, the start or run capacitor could be bad, or they could be good and your compressor could be frozen.

One of my Penguins had this issue, I first replaced the PTC start element and start and run cap and made sure the wiring was good. Those things didn't fix the issue, so I concluded that the compressor had frozen and bought a new unit. It drew 70A before the thermal switch in the compressor tripped!

If the compressor runs (you either hear it or see the current increase) but the system does not cool, it needs a charge. I had one with this issue as well, it had a pinhole leak in one of the refrigerant pipes. I did not have any luck getting an A/C person to look at mine, I ended up replacing that one as well. As I mentioned above Dometic considers the sealed refrigerant system non-repairable, but you may have better luck in your area.

Good Luck!
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Old 06-03-2018, 07:13 AM   #6
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My AC fun continues. I ended up buying a Dometic 641816CXX1J0 Penguin II 410 Amp low profile...

And a conversion board for my 5-button thermostat.

At this point I hired an RV Tech who took things over, thankfully, and installed that heavy thing on the roof. All went well until about 6-7 minutes into the cooling when the fan shut off but the compressor was more than happy to continue it's burden of the work.

It was a hot day so we let the fan cool down. Tried again and exact same thing happened. The tech did notice the fan was drawing almost 5 amps which he said was excessive.

The current logic is that the high current draw is causing the fan to overheat and to protect itself shut itself off after around 6 minutes which is very consistent as we've tested that many times.

We're guessing that it's a bad fan assembly and hope Dometic agrees and sends a new fan.

Of course if Dometic suggests something otherwise that fixes it then I'd be happy with that.

An interesting thing, the conversion board I purchased looked identical to the board in my old unit with the exception of newer looking parts. I believe I could've saved about a $100 and moved the board from the old unit to the new unit.

Would it make any sense, or is it even feasible, for me to buy the newer thermostat CCC2 for the new unit with its original control board and run the communication cable for the bedroom unit (Still older AC) to the existing 5 button thermostat. So I'd have two thermostats.

As usual, thanks for any and all assistance.
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Old 06-03-2018, 01:32 PM   #7
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A quick update.

I purchased the CCC2 Dometic Thermostat from Camping World plugged it up and the AC has been running for 4 hours.

Next step is to run a temporary control cable through the ducts to the old Dometic five button thermostat so I can have two AC units running.

I'll let you know how it ends.
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Old 06-03-2018, 08:28 PM   #8
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This will be my final update on the AC issues which resulted in replacing the failed AC with a Dometic Penguin 2, I also purchased a conversion board to work with my 5 button thermostat.

With this setup both ACs worked but the Penguin II would shut off after about six minutes.

I purchased a new CCC2 and hooked it up and it worked, but of course the older unit in the bedroom doesn't work on the newer thermostat. So I figured I'd wire the older 5 button thermostat directly into the older unit so I could use both on these hot days. Unfortunately it didn't work, I suspect it was because I wasn't getting the necessary DC voltage.

I gave up. Way beyond me at this point.

I'll start saving my pennies so I can replace the back AC unit.

Thanks for everyone's assistance.
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Old 06-03-2018, 08:39 PM   #9
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Quote:
Originally Posted by Mitchone View Post
This will be my final update on the AC issues which resulted in replacing the failed AC with a Dometic Penguin 2, I also purchased a conversion board to work with my 5 button thermostat.

With this setup both ACs worked but the Penguin II would shut off after about six minutes.

I purchased a new CCC2 and hooked it up and it worked, but of course the older unit in the bedroom doesn't work on the newer thermostat. So I figured I'd wire the older 5 button thermostat directly into the older unit so I could use both on these hot days. Unfortunately it didn't work, I suspect it was because I wasn't getting the necessary DC voltage.

I gave up. Way beyond me at this point.

I'll start saving my pennies so I can replace the back AC unit.

Thanks for everyone's assistance.

Usually the rear A/C is jumpered off the front one, just to see if the rear A/C works, you could get a long data cable, plug it into the rear A/C and run it up to the 5 button thermostat and see if it works, you will have to do a reset on the 5 button thermostat.

With the data cable hooked up, the 5 button should recognize the rear A/C.
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Old 06-03-2018, 08:50 PM   #10
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Thatís pretty much what I did except with a difference. I took the five button thermostat on the roof and connected it directly to both ports on the control board. I saw where it was connected directly to the front unit. When I connected it directly to the com ports I didnít get power to the five button thermostat.
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Old 06-03-2018, 09:02 PM   #11
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Hmmm, maybe someone with some more expertise will chime in, hate for you to spend more money when you have a perfectly running A/C unit.


Do you have the troubleshooting manual for the 5 button thermostat?


Maybe some dip switches need to be moved?


The Comfort Control


Center requires DC voltage


to be supplied to the


red (positive +) and


black (negative -) leads


of the control box or


power module.





The rear A/C will be Zone 1, and all dip switches off.
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Old 06-03-2018, 09:03 PM   #12
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Totally agree. Thanks so much.
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Old 06-04-2018, 06:48 AM   #13
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I actually didn't see your entire post describing that the control board needs 12vdc power applied. I did assume that's what I was missing but was not sure where to tackle that problem.

I'm heading to Orlando for a week on Friday, it's still a work week for me so I won't be able to look at this problem until I get back. If I see the current AC unit can't handle keeping my rig comfortable I may need to see about finding a good tech to come by and look into running DC up to the control board, however, I did see some loose DC cables in there with no power to them, I just need to figure out where they go and put a fuse in the DC breaker panel and terminate those leads to the appropriate places on the control panel.

Thanks so much, you've given me a bit of hope and a lesson learned to read the entire message, which in my feeble defense I didn't realize the message continued.

Above all, thanks again
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Old 07-30-2018, 12:43 PM   #14
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Looking to replace my HP for an AC Only unit?

I have a 2007 NEWMAR All-Star with two Dometic units. The rear has already been replaced and is a high profile A/C only unit. The front unit is still working, but seem VERY power hungry and blows cold air, but not arctic air and occasionally pops the breaker on hot days. I'm in the Southwest and I don't really care for the whole HP thing when I really need AC at the lowest power consumption I can get. 110 F is not out of line in Vegas and when driving with hot de-rated ONAN Quiet Diesel 7500 GenSet running, I would like the get the best bang for the buck. This old HP strikes me as the wrong answer. So I was looking at the Dometic 641816CXX1J0 AC unit. I have a 5 button Thermostat that runs both units #1 (Front) and #2 (Rear) ducted intake and exhaust. Is this the right unit for the job with the correct control card installed? Thoughts?
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