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Old 06-26-2019, 01:09 AM   #1
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Brand: Thor Motor Coach
Model: Chateau 31W
State: Minnesota
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THOR #14057
AC ducted air flow,,,

Our rig is in my signature. We have a Coleman Mach 1300 btu AC unit. The AC unit blows cold air. It has the quick cool down vents when open blow massive amounts of air by design. The issue I have is very little air flow from ceiling ducts to the rear of coach.vs the front of coach ahead of AC unit. I have closed both the quick vents thinking that it would boost ducted air flow.Not so much. I do understand that the duct runs behind the AC units to rear of coach are longer and could factor into diminished air flow. Am I missing something or is it just what it is? We do have fans to help, but can I increase ducted air flow. We will be in the Bad Lands next month and anticipate the use of AC.

2017 31W 9K miles.

Thanks
JJ and PJ
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Old 06-26-2019, 01:54 AM   #2
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Brand: Thor Motor Coach
Model: Hurricane 31D
State: Virginia
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THOR #5638
Different older coach model but same problem, low air volume from front ducted A/C to the rear of the coach. I ended up running a 15 foot endoscope down the vent ducts. My problem is poor vent duct sealing and possible leaks into the area above the ceiling and below the roof. Actually I wouldn't call what I have ducts either. More like styrofoam blocks piece together to make an air channel.

There is one thing to check that is fixable. Pull off the ceiling unit cover and check for possible leaks between the supply and return sides of the unit. Use foil tape to seal and potential leaks.
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Old 06-26-2019, 01:56 AM   #3
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Model: Tuscany
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all i can say

is you loose a ton of air flow volume through the ducts
i would start by removing the ceiling cover and open up the plate that blocks off the air and directs it to the ducts. then look inside and make sire the duct is open and the air is going in them vice between


if you only have one roof a/c then you may just have to close the ducts in front if you want cool air to the rear.
my bus has two units so i installed dampers that prevent the front ac air from going past the kitchen and the rear one only cools the bath ad bedroom.


simple physics is there is not enough air volume to blow hard to the rear


a floor fan may help to move air aft
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Old 06-26-2019, 03:08 AM   #4
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I found some small leaks where the AC would turn into the inner roof vents. I taped them off and smoothed out the air flow.

We talked about this some last year. What we discovered was the AC ducts where just channels cut into the roof foam insulation. One member told us to block the ends of the runs (last vent in the front and the last vent in the back of each channel) then cut the foam at 45 deg angle to make the air flow quicker out the last vents. And finally to block the remaining channel off (That when into a dead end) with something as well.

We also cut the last vent cover its self in each channel (it has a black colar around it that would block our modified vent channel). This smoothed out the air flow.

On my axis the channels were open to the bulk head in front of the drop down bunk. So this cool air was doing nothing to cool in inside cabin air and was wasted. I stuffed insulation inside the bulk head to help keep heat (and cold) out.

By blocking all of these leaks and modifying the covers I greatly increased the air flow in the entire system.

I did one at a time then tested with the AC running....you can tell the diffrence right away and it speeds up the cooling of the RV greatly. One of my favorite "Free mods" (well if you have the tape and leftover insulation its free).

Plus I pulled out a coupe of chucks of loose foam blocking the vents.
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Old 06-26-2019, 03:21 AM   #5
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Model: Tuscany
State: Texas
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Quote:
Originally Posted by Long & Winding road View Post
I found some small leaks where the AC would turn into the inner roof vents. I taped them off and smoothed out the air flow.

We talked about this some last year. What we discovered was the AC ducts where just channels cut into the roof foam insulation. One member told us to block the ends of the runs (last vent in the front and the last vent in the back of each channel) then cut the foam at 45 deg angle to make the air flow quicker out the last vents. And finally to block the remaining channel off (That when into a dead end) with something as well.

We also cut the last vent cover its self in each channel (it has a black colar around it that would block our modified vent channel). This smoothed out the air flow.

On my axis the channels were open to the bulk head in front of the drop down bunk. So this cool air was doing nothing to cool in inside cabin air and was wasted. I stuffed insulation inside the bulk head to help keep heat (and cold) out.

By blocking all of these leaks and modifying the covers I greatly increased the air flow in the entire system.

I did one at a time then tested with the AC running....you can tell the diffrence right away and it speeds up the cooling of the RV greatly. One of my favorite "Free mods" (well if you have the tape and leftover insulation its free).

Plus I pulled out a coupe of chucks of loose foam blocking the vents.

i did almost all of that as well on ours
the foam board had a few humps and the end of the run was not sealed, which led to air flowing in the attic space
really surprises me at our Crappy things are done at the factory
a little attention to detail goes a long way
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Old 06-26-2019, 04:47 AM   #6
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THOR #14057
Sounds like I need to do some investigating based on some of the posts. These give some direction.

Thanks
JJ and PJ
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Old 06-26-2019, 11:35 AM   #7
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I had a similar problem in my 24F. I took the diverters off the ceiling and looked inside. What I found was not all of the duct openings were completely cut open. About half of the duct openings were 1/2 to 3/4 cut out. I took a utility knife and trimmed to holes so they were completely open. Seemed to fix my problem.
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Old 06-26-2019, 01:02 PM   #8
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THOR #14057
@jimbo12.

Ill check that out.

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JJ and PJ
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Old 06-28-2019, 01:17 AM   #9
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THOR #14057
Update,,,

I removed the two diffusers in the bedroom (picture attached of one duct) I shined my flashlight into remaining diffusers and they all look the same. So if I were to cut back the opening on the leading edge of air flow I ‘should’ get a bit of air flow improvement?
Anything else? I haven’t pulled the AC cover panel off yet. Would that reveal any other issue?

Edit,,,the picture shows the leading edge of duct from the ac unit.

Thanks,
JJ and PJ
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Old 07-04-2019, 08:39 PM   #10
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Brand: Thor Motor Coach
Model: Chateau 31W
State: Minnesota
Posts: 206
THOR #14057
AC ducted air flow,,,UPDATE

I borrowed a borescope today and have done some investigation. There is some residual styrofoam pieces in the passenger side air channel leading to the vent in the bedroom. Its about 3 feet in and I have been trying to snag it out with a piece of 12 gauge wire. Not successful yet. Looking down the air channel above the fridge towards the rear I see a metallic piece that is the width of the channel located about 3 feet in. The picture quality is poor as I took a picture of the screen on the scope. Im not sure what this would be?

Thanks
JJ and PJ
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Old 07-05-2019, 03:37 PM   #11
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Model: Vegas 2018 24.1
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JJmon,

If your AC is centrally located, perhaps a circular directional vent beneath the blower for the front of the coach and then completely seal off the front ducts coming from the blower. Should improve flow to the rear but I think the rear air will always be a little warmer compared to what comes directly from the blower. It seems to me that even without air leaks in the ducts the roof is plenty hot and not insulated so the air temp increases as it travels though the ducts.
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