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Replacing Dometic DuoTherm A/C Units


Jim Gell

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One of our two Dometic DuoTherm roof mounted air conditioners stopped blowing cold air today. I think they are 13,000 btu.


I am wondering what to do. Here are my thoughts and questions in a somewhat random order:


1) Trailer spent most of it's life in GA, so I would think they have significant hours on them. Based on trailer build date, they are over 11 years old. With the age of these units, it may be cheaper and less hassle to replace them both now, rather than try to repair the broken one and end up replacing both of them in the near future. So how long do these things last? Am I wrong to just replace both rather than repair one?


2) Our trailer measures around 13 feet 4 ½ inches high at the top of one of these A/C units. I would be more comfortable with a replacement that was not as high.


3) From what I have read on the forum, these tall older Dometic units are quieter than some newer models. I don't know if it because of the ducted installation, or the design of the units themselves, but the noise from ours has been minimal and we were happy with them. How much could this change for the worse if we replace with a different model? What brand models would be good (or bad and avoided)?


4) Are these units still made, or do I have to replace with something different anyhow?


5) We have a single control unit that controls both A/C units and both furnaces linked to two zone temp sensors. Seems like I read keeping with Dometic units would make life much easier because we would not have to install new controls or re-size/adapt the roof openings. True?


6) Should I replace them myself,or hire someone? If we hire someone, who would be recommended? We are in AL and headed for TN then OH. We could stop in Elkhart area.


7) Where would a good source be to buy new units?


8) What have I missed?


All help appreciated,


Jim

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2001 Volvo 770, Detroit 60 Series, Gen 2 Autoshift

Passenger assist elevator to enter cab - for when we need it, or sell it?

'05 Travel Supreme Select 40 RLQSO 5th wheel

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We started full timing on December 1st 2014

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In my opinion, much depends upon what the problem is. If you mean that it blows but air don't get cold,does the compressor run and not cool, or does in fail to start? Or do you mean that the blower doesn't blow air? Or is there something else completely? It could be something as simple as a start capacitor that can be replaced quite cheaply, or it could a major issue like a compete loss of refrigerant or some other expensive issue.

 

An air conditioner that has a lot of hours of use will probably have a life span of 10 - 15 years but some last far longer. Any way that you look at this there is a gamble involved as no repair comes with a guarantee that some other part will not fail next week.

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

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Kirk, it blows air, but it is not cold. If there is something simple and relatively cheap that might fix it, I would consider doing that if there is a reasonable chance of getting several more years out of these.

Volvo+and+Travel+Supreme+400+x+103.jpg

 

2001 Volvo 770, Detroit 60 Series, Gen 2 Autoshift

Passenger assist elevator to enter cab - for when we need it, or sell it?

'05 Travel Supreme Select 40 RLQSO 5th wheel

2016 smart car

 

We started full timing on December 1st 2014

Travel is fatal to prejudice, bigotry, and narrow-mindedness - Mark Twain
Not all that wander are lost - J. R. R. Tolkien

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Yes there are other possibilities but someone would need to diagnose it. As Kirk said it could be as simple as a start capaciter or adding something called a "hard start kit" which consist of a capaciter and a relay. It could be a thermal switch that shuts down the compressor if it gets too hot but "usually" resets on its own after it cools down to a certain point. That is usually and indication of something else like the coils. It "could" be as simple as blocked condensor coils on the roof or evaporator coils normally inside. It also could be something in the controls/ thermostat. One thing that needs to be determind is if the compressor itself is actually kicking in. With the power off and the cover off you can back wash the condenser coil with plain water. You have to do it from the side the air exits the coil. It is a good idea to kind of cover the motor electrical stuff just to be careful or let it dry for a couple of days. Don't use a real powerfull stream of water as you can bend the fins on your coil. You need some power but not too much. If your fins are already bent up pretty bad you can carefully straighten them some. If you can get an estimate on the cost of a diagnosis you can decide for youself if you would rather just replace. It is sort of a gamble but could well be worth it. I have seen some go out quick and some last a really long time. I got a window unit going last year by taking it out of the window and cleaning the coils. I am not good at some of the controls/thermostat so that might be better for someone else. I replaced the one on my TT with just an exact changeout by searching out a new one that someone had in stock even though they didn't make the same one anymore. I paid a few dollars more and had to drive a little further but ulitimately saved time and money.

 

There are a fair amount of easy things and a few a little harder. If you don't know much about it and can't pick it up it would probably be best get someone that knows to do it. Might be some stuff about it on youtube. Boy didn't I get long winded.

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I would start by going "up top" and removing the shroud so that you can see inside, then have your helper turn on the unit so that you can observe whether or not the compressor is starting. If it isn't, look at things carefully to see if you can find any signs of a capacitor failure as they usually look different when that has happened. Be very careful where you put your fingers even with the a/c turned off as a capacitor stores electric power and they bite really hard! Even if you pay someone to replace one, a capacitor is not terribly expensive to have done and doing so yourself isn't difficult and will cost less than $50. If you don't do electrical things, see if one of the nearby RV folks does as there are many out there who understand enough of the basics to do this sort of repair.

 

While it is possible that your problem is from the thermostat, that isn't probable in this case based upon my experience. I have found that RV techs who are good at air conditioners are not common place so be careful who you select. I have found that mobile techs are usually more reliable for a host of reasons. Many RV dealers just replace things like air conditioners and refrigerators because they don't know enough to trouble shoot one.

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
Kirk & Pam's Great RV Adventure

            images?q=tbn:ANd9GcQqFswi_bvvojaMvanTWAI

 

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5) We have a single control unit that controls both A/C units and both furnaces linked to two zone temp sensors. Seems like I read keeping with Dometic units would make life much easier because we would not have to install new controls or re-size/adapt the roof openings. True?

Someone correct me if I am wrong. I believe with very few exceptions the roof opening is standard for RV roof air conditioners. About 14" I think.

Al & Sharon
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The Open Range 5th wheel we have is set to have two A/Cs. We have thought of putting a mini-split into the forward bay just to cool down the bedroom in the evening. These only use 500 to 750 W as opposed to the over 2 kW required by the Dometic in living room. The forward sky panel is wired for 110 AC and mini-splits are available at 110 and 220 V AC and for 12, 24, and 48 V DC. Our battery suite is 48 V nominal.

 

Has anyone had experience with mini-split additions or replacements.

 

Reed and Elaine (it was 52 last night here in San Miguel del Allende)

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We had to change one Dometic low profile a few years ago because of a botched repair on the old one. Otherwise we would have kept the old unit, it would have been much cheaper. New ducted Dometics require new thermostats and old units cannot work with the new thermostats, so you have to retro-fit the electronics on the new unit or replace all A/C units. The wiring works. The ducting layout is different between the low profile and high profile units, so you can't mix and match. Retro-fitting the new A/C consists of taking the board off the old A/C and making a couple wiring changes to it that Dometic does document. If the installer says it can't be done, find someone who knows better. I know places in Portland OR (Laurelhurst Distributors (503) 236-2679) and Kissimme (Orlando) FL (R V Gas Appliance/Ac Mobile (407) 870-9842) that know how to do it correctly.

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A couple days ago one of my 15 year old Dometic Penguin heat pumps stopped working completely. No fan, no nothing. I turned off the breaker and pulled the cover from the electronics compartment. I checked for 120V power by turning on the breaker while I tested it, I then checked that the 3 amp fuse on the control board was good and that I was getting 12V through it. Finally I unplugged and reattached all the connections on the circuit board. Presto! It works. After all these years it could be as simple as re-seating all the connections. They can build up corrosion in time. Its worth a try and very inexpensive.

2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter

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Reed, I've often thought of putting a mini-split into one of our custom built trailers. And I may in the future, and set it up for running off a 48 volt battery bank. In my case I'd put the condenser under the coach, where our genset is now - next to the genset. There is plenty of space under there for it. You just have to make sure that you get a unit that can have a pipe run as long as you need it....not all units can tolerate a run that far - some have restrictive limits.

 

You also have to have enough wall space to mount the interior air handler. In the case of a custom coach that is a little easier if you do it during design.

 

You might consider some of the commercial truck (HDT) units. These have vibration mitigation in them. Using a residential unit on an RV may be problematic because of vibration. The issue with the truck units is output, but there are some that will do one ton.

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If you have a 5 button Dometic thermostat turn it off.

 

Then hold down the mode and zone buttons at the same time.

 

While holding them both in turn the thermostat back on..

 

That is doing a reset on the system.

 

If there is FF showing when you turn it on that shows the system has all functions

 

If there is an EE then there is an electrical control problem.

 

If that does not fix it then someone needs to check the components one at a time.

 

Safe Travels, Vern

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Thank everyone for their suggestions. Vern wins the prize this time. I did the reset he suggested and it showed FF. Then I turned on the AC unit that was not working before and it is blowing cold! Thank you Vern!

 

I hate to admit it, but I think I was told how to do this reset a year or two ago and forgot it. I think I may have early onset CRS. I asked Cathy to be in charge of remembering this for next time.

 

Again, thank you all. You gotta love this forum and all the fine folks helping others here.

Volvo+and+Travel+Supreme+400+x+103.jpg

 

2001 Volvo 770, Detroit 60 Series, Gen 2 Autoshift

Passenger assist elevator to enter cab - for when we need it, or sell it?

'05 Travel Supreme Select 40 RLQSO 5th wheel

2016 smart car

 

We started full timing on December 1st 2014

Travel is fatal to prejudice, bigotry, and narrow-mindedness - Mark Twain
Not all that wander are lost - J. R. R. Tolkien

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Glad it was a simple fix. Just a note while on this subject. We replaced 1 Dometic on our Teton. It is louder. It is noisier. It cools better. We did keep the older thermostat but they wired in a new inter phase box on new unit.

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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