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Old 08-25-2020, 12:20 PM   #1
GHallof
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Dometic Ducted AC and CT Thermostat Lessons Learned

2017 3661RL

HOPE SOMEONE FINDS THIS USEFUL - AS FOR ME...MY NEXT STEP IS TO SELL IT.

There is a lot of information regarding issues with the Dometic ducted AC systems on the site. In my case I have two Dometic CT capacitive touch thermostats, controlling a Blizzard NXT 15k in the rear and a Penguin 15K in the front. I like many others have been plagued by the issues, and there appears to be no “exact” fix. Dometic and Keystone seemingly have completely looked away from what appears to be an ongoing problem since about 2015 based on my research.
Contact Dometic and they love to respond by sending you new thermostats or the faceplates. I guess they have had good results lulling folks into believing the issue is fixed by pacifying them with some response at least.
Folks describe the same issues over and over. (Not just Keystone Customers)
Thermostat issues: Temperature Accuracy. Touch controls seeming change on their own or with a simple brush of clothing.
AC Unit Issues: Units don’t run correctly on anything other than HIGH FAN (Maybe). Units shut off sporadically for no reason at all and will not restart without a reset. Units cycle, run for a few seconds shut off, then restart over and over.
I’m sure there are other scenarios and more than likely the few that I described I didn’t get completely right.
The bottom line – THIS STUFF DOESN’T WORK THE WAY IT SHOULD. No end in sight, no matter how much troubleshooting you or your preferred RV repair service does.
In my particular situation I am out of warranty as I am the second owner of the trailer, and based on what some others have gone through getting the issue looked at, I am not willing to pay the labor rates for the many hours of investigation. So…I either live with what I have and attempt to improve my scenario or eat the cost of some other AC solution and trash what is there. IM CHEAP!!
At this point I made the choice to IMPROVE my current system as best that I can in the hopes of alleviating/eliminating the problems.
Nothing that I list below hasn’t been discussed previously on the site. I just wanted to put it all together in a list for folks.

1. Thermostats – If you are having issues where your thermostats have a mind of their own. Reach out to Dometic support and obtain new faceplates. If you continue to have issues keep communicating with them until another set of faceplates, or complete thermostat replacements alleviate the “mind of their own” issue. Believe me they love to send these things out. Examples of this are where the thermostats change settings on their own.
Insulate the cavity behind the thermostat – I found that the heat in the wall was causing severe problems with temperature accuracy. I was able to use a combination of rolled insulation and spray foam to provide enough surface area behind the thermostats that allowed them to pick up the ambient temperature in the room vs. fight with the heat in hollow wall cavity.
While you have the thermostat off the wall. Check the wiring job. Clean it up. Even though mine were wired appropriately I found one thermostat to have wire exposure in the insulation further down the wires from the terminals.

2. Duct Work – Specifically check for collapsed duct work for your WARM air returns. All of my warm air returns were collapsed. I used two 9” pieces of 1.25” PVC on either side of each duct to open them up. Right off the bat there was a significant increase in the performance of the system. I checked my cold air supply duct work and found all to be OK. A bore scope helps.
Check all cut openings in the duct system – Both warm and cold air ducts at their cut opening points need re-tapped ensuring a positive seal. INTERIOR: For the cold air diffusers inside the 5ver this will ensure that cold air being pushed from the AC units flows fully into the trailer and not between the duct and the ceiling panels. For the warm air returns it will ensure that supply air back to the AC is pulled from the 5ver interior and not the cavity between the roof and the ceiling. Almost all interior cut openings in my case had to be re-tapped so I redid them all. The foil tape was either junk to start with or deteriorated enough over two years that all openings separated. EXTERIOR: Yep there are cuts on the roof to check. Get up on the roof and pull the covers off your AC units. Remove the plenums and you will see one hole for your warm air returns and the other hole will be for the cold air supply. You should see where the same tape was used to seal both openings to their respective ducts. In my case there were huge gaps where the openings, both front and rear locations, had separated. Once again allowing cold air into the roof/ceiling cavity and warm air to be pulled from the cavity. NOTE: Bring a vacuum to get all the wood chips from the factory picked up.

3. AC Unit Mount Position – While you’re on the roof pay attention to the positioning of each AC units with respect to the openings cut at the factory. I had to reposition my front AC unit 2” forward as it was out of alignment with the holes that were cut. Essentially allowing the recirculating of cold air leaving the system right back into the warm air return. NOTE: At a minimum make sure the AC mounting gasket is present in between each of the holes cut in the roof.

4. Cold Air Diffusers – Two things here. First trim the base/collar that inserts into the ceiling to ensure it doesn’t protrude into the duct restricting air flow. Second, optional, remove every other vent blade to allow increased air flow exiting the duct. Or just buy new diffusers that have a shorter collar length and are more open to better air flow. I’m CHEAP. If you take your time removing the blades/fins it looks good and works great.

5. Vented Steps – My steps are vented directly to the basement. Not sure if all 5vers are like this or not. I removed my basement wall to expose the back side of the steps. I was able to fashion a piece of black vinyl sheeting so that would act as a damper to block warm air being actively drawn into the living space.

In the end. I feel I am light years ahead of where I was at. I am not willing to say that all is fixed at this point but time will tell. However, my unit has been hooked up next to my barn for the last three weeks. Temps here in Ohio have been in mid 80s to 90 and humid with a few cooler days. Both TStats have been set at 75 and on AUTO. So far no issues. No shutdowns. No cycling. Knock on wood. You watch I’ll check everything tomorrow to find it off line. Even if that is the case. The system, when it runs, runs effectively now and doesn’t struggle like it used to.

If anyone has any questions. Please feel free to reach out.

Thank you to all the previous posters for their informative posts that allowed me to step thru all of this.

Use caution on the roof and make sure all systems are shut off prior to any work being conducted.

Gordo

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Old 08-25-2020, 01:43 PM   #2
Daryles
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Great write up.
Thanks for putting this together.
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Old 08-26-2020, 05:23 AM   #3
RMcNeal
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Awesome write up, Gordo. I shoulda known a marine would find some way to make the situation livable. Improvise, adapt and overcome! Hooorah!
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Old 08-26-2020, 05:38 PM   #4
vickytallman
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Please - Newbie Needs AC Help

"2. Duct Work – Specifically check for collapsed duct work for your WARM air returns. All of my warm air returns were collapsed. I used two 9” pieces of 1.25” PVC on either side of each duct to open them up. Right off the bat there was a significant increase in the performance of the system. I checked my cold air supply duct work and found all to be OK. A bore scope helps.
Check all cut openings in the duct system – Both warm and cold air ducts at their cut opening points need re-tapped ensuring a positive seal. INTERIOR: For the cold air diffusers inside the 5ver this will ensure that cold air being pushed from the AC units flows fully into the trailer and not between the duct and the ceiling panels. For the warm air returns it will ensure that supply air back to the AC is pulled from the 5ver interior and not the cavity between the roof and the ceiling. Almost all interior cut openings in my case had to be re-tapped so I redid them all. The foil tape was either junk to start with or deteriorated enough over two years that all openings separated. EXTERIOR: Yep there are cuts on the roof to check. Get up on the roof and pull the covers off your AC units. Remove the plenums and you will see one hole for your warm air returns and the other hole will be for the cold air supply. You should see where the same tape was used to seal both openings to their respective ducts. In my case there were huge gaps where the openings, both front and rear locations, had separated. Once again allowing cold air into the roof/ceiling cavity and warm air to be pulled from the cavity. NOTE: Bring a vacuum to get all the wood chips from the factory picked up.

4. Cold Air Diffusers – Two things here. First trim the base/collar that inserts into the ceiling to ensure it doesn’t protrude into the duct restricting air flow. Second, optional, remove every other vent blade to allow increased air flow exiting the duct. Or just buy new diffusers that have a shorter collar length and are more open to better air flow. I’m CHEAP. If you take your time removing the blades/fins it looks good and works great."



So - I am a complete newbie when it comes to 5ver's period. My 2016 Montana 3820FK. The A/C units (both of them) are severely troublesome. I have already contacted Dometic regarding the thermostats, thanks to the other posts.

The AC in the bedroom works fairly good, and keeps the temp, as long as the fan is set to High. It doesn't work at all at any other time.
The AC in the living room works (on HIGH fan), but it does not cool down like it should.
I have read that I should check the duct work, but I have absolutely no idea how to do this. I don't know which return goes where, etc.. I know where the vents are in the ceiling with the little pieces of foam.
Does anyone have any pictures or a blow by blow of how to check these?
Any help, ideas, hints, anything would be so much appreciated!

Vicky
17 year DoD - Support your Services!
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Old 08-26-2020, 07:24 PM   #5
Ahdmeyer
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this is a grand designs but it may be the same units dont know interesting article

al meyer3931fb az
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Old 08-27-2020, 06:46 AM   #6
GHallof
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Duct Repair

Hi Vicky maybe this will help. Two types of ducts. Warm Air and Cold Air. The vents with the foam are warm air. Air is pulled in through these up into the plenum of the AC Unit flows through the unit and then into the cold air duct. See below. To determine if your ducts are collapsed (I would start with the warm air) Remove the vent holding the foam, and then remove its base that holds it to the ceiling. Youll end up being able to see the rough opening. This opening will be, or at least should be taped (sealed) to the duct. Place your hand inside, in the middle, of the duct facing towards the AC unit. The ducts are made out of a foam material. Over time the top of the duct sags restricting air flow. See example in image. To fix. You can insert lengths of PVC to open the duct back up and restore air flow. Take your time and use caution not to rip the foam as you insert the PVC sections. Use 1.25" PVC in 9 or 10" sections. The idea is to open as much of the length of the duct as possible. The cold air ducts are more difficult but can be accomplished similarly.
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Old 08-27-2020, 09:35 AM   #7
scottz
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Nice drawing. Makes it easy for people to see how one AC unit can freeze up the other. Mine have been doing it since new. Running the fans on high prevents it.
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Old 08-27-2020, 11:27 PM   #8
Mikelff
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Quote:
Originally Posted by GHallof View Post
2017 3661RL

HOPE SOMEONE FINDS THIS USEFUL - AS FOR ME...MY NEXT STEP IS TO SELL IT.

There is a lot of information regarding issues with the Dometic ducted AC systems on the site. In my case I have two Dometic CT capacitive touch thermostats, controlling a Blizzard NXT 15k in the rear and a Penguin 15K in the front. I like many others have been plagued by the issues, and there appears to be no “exact” fix. Dometic and Keystone seemingly have completely looked away from what appears to be an ongoing problem since about 2015 based on my research.
Contact Dometic and they love to respond by sending you new thermostats or the faceplates. I guess they have had good results lulling folks into believing the issue is fixed by pacifying them with some response at least.
Folks describe the same issues over and over. (Not just Keystone Customers)
Thermostat issues: Temperature Accuracy. Touch controls seeming change on their own or with a simple brush of clothing.
AC Unit Issues: Units don’t run correctly on anything other than HIGH FAN (Maybe). Units shut off sporadically for no reason at all and will not restart without a reset. Units cycle, run for a few seconds shut off, then restart over and over.
I’m sure there are other scenarios and more than likely the few that I described I didn’t get completely right.
The bottom line – THIS STUFF DOESN’T WORK THE WAY IT SHOULD. No end in sight, no matter how much troubleshooting you or your preferred RV repair service does.
In my particular situation I am out of warranty as I am the second owner of the trailer, and based on what some others have gone through getting the issue looked at, I am not willing to pay the labor rates for the many hours of investigation. So…I either live with what I have and attempt to improve my scenario or eat the cost of some other AC solution and trash what is there. IM CHEAP!!
At this point I made the choice to IMPROVE my current system as best that I can in the hopes of alleviating/eliminating the problems.
Nothing that I list below hasn’t been discussed previously on the site. I just wanted to put it all together in a list for folks.

1. Thermostats – If you are having issues where your thermostats have a mind of their own. Reach out to Dometic support and obtain new faceplates. If you continue to have issues keep communicating with them until another set of faceplates, or complete thermostat replacements alleviate the “mind of their own” issue. Believe me they love to send these things out. Examples of this are where the thermostats change settings on their own.
Insulate the cavity behind the thermostat – I found that the heat in the wall was causing severe problems with temperature accuracy. I was able to use a combination of rolled insulation and spray foam to provide enough surface area behind the thermostats that allowed them to pick up the ambient temperature in the room vs. fight with the heat in hollow wall cavity.
While you have the thermostat off the wall. Check the wiring job. Clean it up. Even though mine were wired appropriately I found one thermostat to have wire exposure in the insulation further down the wires from the terminals.

2. Duct Work – Specifically check for collapsed duct work for your WARM air returns. All of my warm air returns were collapsed. I used two 9” pieces of 1.25” PVC on either side of each duct to open them up. Right off the bat there was a significant increase in the performance of the system. I checked my cold air supply duct work and found all to be OK. A bore scope helps.
Check all cut openings in the duct system – Both warm and cold air ducts at their cut opening points need re-tapped ensuring a positive seal. INTERIOR: For the cold air diffusers inside the 5ver this will ensure that cold air being pushed from the AC units flows fully into the trailer and not between the duct and the ceiling panels. For the warm air returns it will ensure that supply air back to the AC is pulled from the 5ver interior and not the cavity between the roof and the ceiling. Almost all interior cut openings in my case had to be re-tapped so I redid them all. The foil tape was either junk to start with or deteriorated enough over two years that all openings separated. EXTERIOR: Yep there are cuts on the roof to check. Get up on the roof and pull the covers off your AC units. Remove the plenums and you will see one hole for your warm air returns and the other hole will be for the cold air supply. You should see where the same tape was used to seal both openings to their respective ducts. In my case there were huge gaps where the openings, both front and rear locations, had separated. Once again allowing cold air into the roof/ceiling cavity and warm air to be pulled from the cavity. NOTE: Bring a vacuum to get all the wood chips from the factory picked up.

3. AC Unit Mount Position – While you’re on the roof pay attention to the positioning of each AC units with respect to the openings cut at the factory. I had to reposition my front AC unit 2” forward as it was out of alignment with the holes that were cut. Essentially allowing the recirculating of cold air leaving the system right back into the warm air return. NOTE: At a minimum make sure the AC mounting gasket is present in between each of the holes cut in the roof.

4. Cold Air Diffusers – Two things here. First trim the base/collar that inserts into the ceiling to ensure it doesn’t protrude into the duct restricting air flow. Second, optional, remove every other vent blade to allow increased air flow exiting the duct. Or just buy new diffusers that have a shorter collar length and are more open to better air flow. I’m CHEAP. If you take your time removing the blades/fins it looks good and works great.

5. Vented Steps – My steps are vented directly to the basement. Not sure if all 5vers are like this or not. I removed my basement wall to expose the back side of the steps. I was able to fashion a piece of black vinyl sheeting so that would act as a damper to block warm air being actively drawn into the living space.

In the end. I feel I am light years ahead of where I was at. I am not willing to say that all is fixed at this point but time will tell. However, my unit has been hooked up next to my barn for the last three weeks. Temps here in Ohio have been in mid 80s to 90 and humid with a few cooler days. Both TStats have been set at 75 and on AUTO. So far no issues. No shutdowns. No cycling. Knock on wood. You watch I’ll check everything tomorrow to find it off line. Even if that is the case. The system, when it runs, runs effectively now and doesn’t struggle like it used to.

If anyone has any questions. Please feel free to reach out.

Thank you to all the previous posters for their informative posts that allowed me to step thru all of this.

Use caution on the roof and make sure all systems are shut off prior to any work being conducted.

Gordo

https://www.montanaowners.com/forums...ad.php?t=81164
https://www.montanaowners.com/forums...ad.php?t=82037
After all that work you’re going to sell it? I would enjoy it for a while first then make a decision. If you are thinking of buying another 5er, you could end up again where you started. You have motivated me to really dig into my duct work to make sure it is all open and working like it should. I changed out my AC plenum cover for one that channels all cold air through the duct work. No more cold air dump vent. It also has some sound proofing built in so it is much quieter. It has worked well so far. Thanks for your write up. One thing you might try is contact the consumer protection agency and file a complaint. I haven’t read of anyone doing that, and it doesn’t cost you a dime. If you do, let us know what you find out.
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Old 08-30-2020, 02:53 PM   #9
Buckfisher
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The vents in the steps are the return air for the furnace. May not be a good idea to block them. If there isn't enough openings for air to get into the lower compartment from the living area, or enough cracks from the lower compartment to the outside air, and enough cracks from the living area to the outside air, the flow through the furnace will be restricted, possibly too much for it to work properly and it may possibly overheat and cause a fire. But I think everything else said was a "slam dunk".
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Old 08-31-2020, 06:49 AM   #10
GHallof
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Hi Buckfisher. Understood. When AC runs the system draws the warm air from the basement thru the steps into the living space ever so slightly. When the furnace runs it pulls its supply air from the basement area. So the interior warm air is pulled back through the steps into the basement in the opposite direction. The material that i used is lightweight. Just enough to be lightly pulled against the slits in the steps when the AC runs. When the furnace runs the material is pulled away from the slits allowing air flow.

Speaking of the furnace air supply...I was amazed to find just how open the basement area is to draw air from outside the rig. A number of large openings between the body and frame structure. I know this from the DANG critters that made the basement area and every other nook and cranny a place t store and eat black walnuts last year. LOL
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Old 08-31-2020, 07:29 AM   #11
John Shasky
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AC improvements

I have a 2014 3402rl. Dual ACs do not keep 5th wheel cool. Granted we live in Southern AZ but when it gets to 85 degrees and higher inside, it is pretty uncomfortable. Outside temp do reach around100 to 105 in the afternoon.
I have added a portable AC that exhausts the hot air through a rear slide out window. It helps a bit.

I wonder where the temp sensors for the system are. Seems like they are not accurate. That might be part of the problem.

The 5er model has black accents on the roof (AC shrouds, roof vent covers etc.).

I think it would help to paint the black items white Not sure what type of paint to use. I did paint the bathroom skylight white o the inside.

Considering giving up and selling!
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Old 08-31-2020, 09:08 AM   #12
Ram2013
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Domestic Ducted AC

Changed out Dometic Ac’s and went with Coleman Units. Best move. The Dometics were junk and experienced all the above issues.
The Coleman’s are like having central air. Low noise and cool for the first time on our 2015 318 RE Highcountry.
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