2023 3123RL Legacy AC Airflow - serious issue

[suny07]

Hi,

last night we encountered a new and major problem with our Montana 3123RL.

We like to run the living room AC during night in the back which normally pushes cold air to the bedroom in the front.
For some reason this did not happen again last night.
Zero air is getting to the ceiling vents in the Bedroom, Bathroom and the 2 last vents in the kitchen in-front of the pantry.
So I thought that's wired and tried the other way round.
Running the front AC is also not delivering air the 6 vents in the back in the kitchen and living room, only to the 2 infant of the pantry, Bathroom and Bedroom.

This morning I went for investigation and opened the ceiling cover of the Maxair fan and removed the air vents around this area to peek into it.
First I stuck a tape measure into the AC Air channel.
At 31.5 inches from the pantry towards the living room the tape measure got blocked.
Then the other way round from the 2 kitchen air vents towards the pantry the tape measure got blocked at around 12 inches.

Then I stuck my phone into the channels to try to take pictures and got some.
On the passenger/door side I look at a wood panel and on the driver side I look at a wallpaper wood piece.
See attached.
There seems to be a blockage on the hight of the prewired outlet for the 3rd AC.

Why could the Airchannel, which is market as a Racetrack, be blocked in that way?
Clearly no air can flow through there.

I tried to poke and push that blockage but no success.

Anyone has inside if this has to be like that? E.g. as prep for a 3rd AC?
Did they maybe mount the airchannel in the wrong way and that blockage should be on the other side at the end of the airchannel at the end of the camper?
How can I get rid of the blockage? This looks like a massive project getting to that position with opening the ceiling etc.

Thanks for input and advice.

Thanks,
Mike

 

[Lee-C]

Good Lord...... I myself never heard of such a thing. Can only speculate this was engineered this way due the the 3rd AC prep. You might call Keystone and ask for recommendations on this one. Otherwise the only way I can envision to remedy this would be to drop the ceiling panel and have two raceway duct joints on hand with which to splice each of the the ducts together.
Maybe others will have firsthand knowledge and make better suggestions.

 

[Bourbon County]

Am I understanding you correctly that previously you have been able to use either unit and would deliver air to the opposite end of the RV, and Suddenly this practice does not work? While investigating you found what appear to be factory installed plywood blocks in the racetrack ducts on both sides? That's way beyond strange!

My understanding is that is the purpose of the racetrack ducts; so you can use only unit under low load conditions, or maybe one unit is broken down. I'm not 100% sure of this, but my understanding was on units that were prepped for a 3rd AC it is meant to be a ductless model.

 

[suny07]

We are not so sure anymore if we had airflow from the back to the front ever.
This unit was purchased last November and this is our first trip in heat.
So far we used the furnace more.

When the 3rd AC's are meant for to be ductless, it makes sense. There is no preparation direct on the racetrack channels.

I am considering to screw through that wood panel multiple holes.

It always happens in the middle of a trip and you have a fun diy project. Yeah, we had other plans...

 

[suny07]

screwing was unsuccessful as I can not get a proper reach

 

[Bourbon County]

You might give this a try:

https://www.amazon.com/1-Inch-54-Inch-Klein-Tools-53720/dp/B007E76498?th=1

 

[foldbak]

We're in the same boat. Readying the RV for a trip today. Yesterday I couldn't get the thing below 90 degrees. Got so frustrated I removed all of the vents. Now I have holes in the ceiling, but at least I can feel cold AC now. In the past I could run both AC's on 30 amps. Yesterday I blew my breaker 3 times. Dog bone was hot! It was 105, today it's 102. Fridge is only 45. Going to be an interesting trip, on 30 amps.

 

[suny07]

We're in the same boat. Readying the RV for a trip today. Yesterday I couldn't get the thing below 90 degrees. Got so frustrated I removed all of the vents. Now I have holes in the ceiling, but at least I can feel cold AC now. In the past I could run both AC's on 30 amps. Yesterday I blew my breaker 3 times. Dog bone was hot! It was 105, today it's 102. Fridge is only 45. Going to be an interesting trip, on 30 amps.

How is your trip going? +100F is a different situation.
Luckily we stay in NC near Asheville and it cools down by default at night.
The strategy was to cool down the front to 66-64 and let the rear run at 64 at night which produced 66-68 in the bedroom at the front.
Without the temperature drop here at location at night I think it would be tough.

I contacted Keystone to see what they think.
The unit is finally still under warranty.

 

[RJS3791RD]

For what its worth……We have a 2022 3791RD with factory front and rear 13.5 Coleman Mach AC units. Our vent system is the ‘race track’ style that connects the front and the rear in one loop. When only the front is on, we have air movement in the rear. Likewise when the rear ac is on when have air movement in the front. We also have the factory prep for third ac. However I can tell you that if/when I do add a third ac unit, I will install a ductless unit that blows down into the kitchen area. I am not sure but it appears to me that the 3rd ac units are not designed to tap into the race track vent system.

If we are on 30amp service or running a small generator, only one ac will function. We can run either front or rear. Just not both. I have considered adding soft starts but I am waiting until I decide if we are going to add a third ac unit or not.

Like others, I am not impressed with the blade style vents. I have removed one in the back, two in the kitchen and one in the front. It has made a huge difference. I am looking at a different style vent to fill the hole

 

[LJSantore]

The soft starts are a game changer. On our last rig it took two generators to start one unit. After the soft start we could do the job with one. I just put one on our home heat pump and the LRA went from 82 amps down to 22 AMPS. On my two Coleman AC units on our 3121 legacy We see 0 LRA the life of the compressors should be dramatically longer without the huge inrush of power to start the unit We run one air conditioner on Solar and I would not even try that without a soft start.

 

[foldbak]

How is your trip going? +100F is a different situation.
Luckily we stay in NC near Asheville and it cools down by default at night.
The strategy was to cool down the front to 66-64 and let the rear run at 64 at night which produced 66-68 in the bedroom at the front.
Without the temperature drop here at location at night I think it would be tough.

I contacted Keystone to see what they think.
The unit is finally still under warranty.

It was 110 on 30 amps. My dog bone took a crap but the resort loaned me one. AC's ran ALL day and night. Heat of the day 95 in the rig. The low at night 61. I removed the filters and dam near doubled the air flow. Removed all the vents. The fridge struggled. 42 to 60. We had no shade so sat in the river all day. The fridge is obviously the priority. We leave for the coast on Thursday which will be a whole difference experience. The high is 63.
I'm wondering if it's worth investing in a roof.
https://rvroof.com/lasting-adventur...MIldSa2viVhwMVt8zCBB1VcQgBEAAYASAAEgLmUvD_BwE

 

[foldbak]

For what its worth……We have a 2022 3791RD with factory front and rear 13.5 Coleman Mach AC units. Our vent system is the ‘race track’ style that connects the front and the rear in one loop. When only the front is on, we have air movement in the rear. Likewise when the rear ac is on when have air movement in the front. We also have the factory prep for third ac. However I can tell you that if/when I do add a third ac unit, I will install a ductless unit that blows down into the kitchen area. I am not sure but it appears to me that the 3rd ac units are not designed to tap into the race track vent system.

If we are on 30amp service or running a small generator, only one ac will function. We can run either front or rear. Just not both. I have considered adding soft starts but I am waiting until I decide if we are going to add a third ac unit or not.

Like others, I am not impressed with the blade style vents. I have removed one in the back, two in the kitchen and one in the front. It has made a huge difference. I am looking at a different style vent to fill the hole

I'm leaving the hole open!

 

[suny07]

For what its worth……We have a 2022 3791RD with factory front and rear 13.5 Coleman Mach AC units. Our vent system is the ‘race track’ style that connects the front and the rear in one loop. When only the front is on, we have air movement in the rear. Likewise when the rear ac is on when have air movement in the front. We also have the factory prep for third ac. However I can tell you that if/when I do add a third ac unit, I will install a ductless unit that blows down into the kitchen area. I am not sure but it appears to me that the 3rd ac units are not designed to tap into the race track vent system.

If we are on 30amp service or running a small generator, only one ac will function. We can run either front or rear. Just not both. I have considered adding soft starts but I am waiting until I decide if we are going to add a third ac unit or not.

Like others, I am not impressed with the blade style vents. I have removed one in the back, two in the kitchen and one in the front. It has made a huge difference. I am looking at a different style vent to fill the hole

Thanks! Guess I have to work with keystone to see how they fix this at our unit.

 

[Mikendebbie]

Screen shots are from one of the many Montana Factory tour videos on Youtube. This one was by Josh the RV Nerd from Spring 2023.

The first screen shot shows how the race-track duct connects to the rear AC. The second screen shot shows the rough opening for the 3rd AC with a note in the lower left corner of the video "Non-ducted 3rd AC unit". The note is obstructed somewhat in the screen shot.

Earlier in the video he shows a stack of prefabbed runs of ductwork in the factory over in the roof-build section. It looks like the factory guys just slide the duct sections into place within the trusses and tape the joints together. It's hard to imagine how an obstruction would get into the ducts - but obviously something crawled into or fell into yours. Sorry for your issues!

 

[suny07]

Screen shots are from one of the many Montana Factory tour videos on Youtube. This one was by Josh the RV Nerd from Spring 2023.

The first screen shot shows how the race-track duct connects to the rear AC. The second screen shot shows the rough opening for the 3rd AC with a note in the lower left corner of the video "Non-ducted 3rd AC unit". The note is obstructed somewhat in the screen shot.

Earlier in the video he shows a stack of prefabbed runs of ductwork in the factory over in the roof-build section. It looks like the factory guys just slide the duct sections into place within the trusses and tape the joints together. It's hard to imagine how an obstruction would get into the ducts - but obviously something crawled into or fell into yours. Sorry for your issues!

very cool, Thank You!

I saw that video but did not think to go and look there how its done.

Waiting on Keystone to get back to me.

 

[Bourbon County]

The units they use like Dometic and Coleman are actually pretty efficient, the shortcomings are primarily in the duct system.

There is a formula for measuring AC efficiency: H1-H2 X 4.5 (constant) X CFM=BTU/HR. If you have access to a psychrometer that will measure enthalpy (look it up) you can measure H1 at a return and H2 at a supply closest to unit. There's no good way to measure CFM that I see; it seems all manufacturers state 350 CFM in their specs regardless of size, that's what I used. Once you calculate actual BTU/HR by the formula, divide it by the unit's rating; either 15K or 13.5K. Mine measured 92% and 94% which is actually pretty good for a residential system. Bear in mind the stated BTU is a nominal number, most residential units have data available on what the exact BTU is. The outdoor temperature will have some effect too; if you measure in outdoor temps between 80-85 you'll see best performance.

Keystone advertises the improved duct connectors and end caps they use, which is a good thing. They advertise long radiused elbows and Tees which are a good thing too. An ideal size ratio for rectangular duct is maybe 1 to 3, or 1 to 4; in other words the duct width should be somewhere between 3 and 4 times the height. The duct insulation is a very good thing since it's located in the ceiling, but the exposed insulation adds a lot of friction to airflow; just a foil lining would be a great improvement. Every manufacturer I've seen specs on states the unit airflow at 350 CFM. Based on residential units, you would want a 15K BTU unit to deliver somewhere between 435-500 CFM. I'm not sure why they keep it low, maybe air noise or because of the high static pressure in the duct? Lastly, the diffusers make a pretty big difference; choose the largest diameter you can fit; when looking at the size, make sure you're looking at opening not outer diameter over the trim ring. I personally like the ones that can be rotated and allows louvers to be adjusted separately. Avoid pointing them at a return; that sets up an air "short circuit"

Obviously, we can't do anything about the duct size, the high friction rate in the duct, or the blower speed/CFM on the units. The only thing that's left is the vent louvers which are cheap and simple to install. Using a low restriction filter element helps too, I'm talking about the nylon "horse hair" type. It's available on Amazon and can be easily cut to fit with a pair of scissors.

Air flow is king on any AC system, most any unit will remove the heat. The secrets to success are delivering the right amount of air to the right place.

 

[suny07]

I have a first feedback from keystone.

According to that our unit was not build with a racetrack air duct system.
It has a H-Frame System - ???

This is because it is prepped for a 3rd AC.

Anyone ever heard about that?
How would that even make sense as the 3rd AC is not supposed to feed into the airducts.

I have the impression they want me to go away.
Quite disappointing.

 

[RJS3791RD]

Hummmm. I have learned that trying to understand what they do or don’t do when building these products will make you crazy. Personally, I don’t buy that you have the H track because of a/c prep. I have the a/c prep package and I have the race track continuous loop. Maybe because mine is 40’ long and they use the race track style to provide coverage in the middle if you don’t put in the third a/c? I defer to some of the more knowledgeable gentlemen on this forum.

Regardless, I too would be a bit disappointed

 

[foldbak]

According to my dealer as of today, the 3rd AC is direct flow not ducked.
We had a long (door closed conversation) regarding AC, refrigerators and black tanks in above 100 degree temps. At the end of the day, you can expect a 20 degree difference from the ambient outdoor temp to the indoor temp in an RV. Quite frankly, I'd prefer direct flow on all my AC's.

 

[Bourbon County]

I have a first feedback from keystone.

According to that our unit was not build with a racetrack air duct system.
It has a H-Frame System - ???

This is because it is prepped for a 3rd AC.

Anyone ever heard about that?
How would that even make sense as the 3rd AC is not supposed to feed into the airducts.

I have the impression they want me to go away.
Quite disappointing.

Could it be possible that both sides of the common racetrack ducts have a Tee at the position a third AC could connect to the duct system when installed? Imagine looking down on it, it would look like an H. Is it possible that the plywood blocks you photographed are blocks for the ends of these sections of ducting?

I can't imagine how inefficient adding a third unit to a ducted system would actually be able effective at all. You're adding an additional 350 CFM of air flow to already undersized ducts, you're adding it near the center of the trunk lines which would only generate more turbulence. If this theory is correct, having sections Tee connected to the trunk lines and capped off, you are still pressurizing that section and getting absolutely no good from it. This looks like a lose/lose situation.

Did you ever confirm if you were or were not getting airflow throughout the coach with only unit running? Even if you can't feel it with your hand, try putting a couple of squares of CLEAN toilet tissue against the vent. It's very light and takes very little air flow to move it.