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Old 04-15-2018, 04:44 PM   #1
Junior Member
 
Brand: Thor Motor Coach
Model: ACE 29.2
State: Virginia
Posts: 24
THOR #9819
Adding Insulation To Coleman-Mach AC Rooftop Unit

While searching for an entry point into our 2012 Thor ACE 29.2 for the weBoost Cell Phone Amplifier (see other recent post), I investigated the possibility of bringing the outside antenna wire down through the AC rooftop duct. Our MH has a Coleman-Mach 3, 13,500 BTU rooftop unit. The air return comes up through the ceiling into a sheet metal housing, through the evaporator coils and then back into the air duct system, all driven by a squirrel cage fan. Drilling a hole through the side wall of the sheet metal housing seemed like an easy, waterproof access point.

Ultimately, I decided to use the weBoost kit and go through the side wall of the RV, but my investigation of the AC system left me with the realization that the air duct wasn't very well insulation. There's an insulation board on the inside of the sheet metal, but it isn't very thick. So I thought, "why not put an added layer of insulation on the outside". Turns out, I had just the material to do it, and that's what this post is about.

I've included some photos to help illustrate my approach.

First, I took off the plastic outer cover (shroud) by removing the 4 top mounted bolts with washers and set them aside.

The forward edge of the housing needs to be pushed towards the front of the MH to release the unit from the small sheet metal "catches" which stick out at the lower edge. These hold it in place. Once past those, the housing just lifts off and I set it aside.

I only covered the larger air duct and not the housing over the heat exchanger fins.

The R17, 0.2" thick insulation is foil faced on both sides with closed cell polyethylene foam in between. I get mine from Prodex (Reflective insulation for metal buildings, pole barns and houses) and use it all around our farm. It comes in 4 ft. widths, is sturdy and lasts a long time. However, I think Home Depot and/or Lowe's also sells something similar. While Prodex sells a 0.4" thick, R22 material, I'm not sure it would work as well as the 0.2" material. After wrapping the sheet metal, the outer housing (shroud) just barely fit over the (now larger) air duct.

To keep the foam/foil insulation in place, I used heavy duty aluminum duct tape from Home Depot.

I wrapped and taped a single piece of insulation onto the housing, trimming where necessary and overlapping on the sides, making sure to leave room around the motor housing because there are air vents which I didn't want to cover.

As long as I had the unit open, I also used my compressed air hose to blow out any dust/debris from the condenser coils to make sure there was easy air flow. I also checked the fan motor shaft to make sure it turned easily and there wasn't a sign of a bearing going bad. Fortunately, it turned easily and continued to spin quite freely once I let go of the shaft.

Then, I reinstalled the outer shroud cover.

As a final test, I went into the MH and turned on the AC, setting the thermostat low enough to ensure the compressor kicked in. The air coming out was about 20F. cooler than the air intake, which is about what I expected. I took that to mean I hadn't broken anything and the unit still worked.

Next, I have to vacuum the inside coils for good air flow and clean the celing AC filters. The fan is quite strong so I think I might try adding a piece of HEPA filter to see if the air flow continues to be good enough and frost doesn't build up on the inside coils. Right now, yellow pine pollen is covering and getting into everything and this summer, I can imagine we'll see lots of dust, so a filter to keep the air clean might be a good idea. My wife wants us to also take along a stand-alone, 120V HEPA filter, which I will most likely do.

And lastly, I plan to paint the outer covering (shroud). Currently, it's black. A new, white one costs $113 plus shipping, but a can of paint made for polypropylene material is much cheaper. "Black" looks very nice and is stylish, but it absorbs sunlight, converting it to heat, which is what the AC is trying to get rid of. Doesn't make much sense to make the unit work harder than it has to.

If anyone else has painted their shroud, please post a reply with do's, don'ts, and tips. Thanks.
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Old 04-17-2018, 05:17 PM   #2
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Brand: Thor Motor Coach
Model: 2013 31L
State: Florida
Posts: 1,989
THOR #908
I've been meaning to paint my black cowling but just never have gotten around to it yet. Outstanding idea to insulate that plenum!

Think I'll add that to my wish list of things to do some day....

Thanks
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Old 04-17-2018, 06:47 PM   #3
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Brand: Thor Motor Coach
Model: ACE 29.2
State: Virginia
Posts: 24
THOR #9819
I ordered the gloss white Rust-Oleum Paint For Plastic ($5.61) because it does polypropylene and the white XIM Plastic & Vinyl NT100 plastics bonding primer ($12.99, also for polypropylene) from Amazon (total with sales tax $19.72). I'm trying the "gloss" in the hopes it is a little more "mirror-like" and bounces more sunlight away.

They just arrived (by mail), but conditions have turned wintry again (47 F. this morning - normal is 60 F.), so I'll have to wait a few days till it warms up. The cans say the paint will be fine. It's more "me" I'm worried about.
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Old 07-20-2020, 04:01 PM   #4
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Brand: Still Looking
State: Virginia
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THOR #19720
Hey this is great! I am about to do my outside cover like you have done.
Did you do anything to the insulation inside that cover? Mine has some funky old stuff in there and I am thinking of removing it or adding a layer of foam board.

Thanks!
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Old 07-20-2020, 05:36 PM   #5
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Model: 2018 24.1 AXISSIXxSIX
State: Arizona
Posts: 2,500
THOR #13932
https://www.amazon.com/Prodex-Total-...pe=all_reviews

It's r1.2 by itself. This is better than rzero and if it all that fits in the ac unit, it's the best that can be done.
Reflectivity requires a gap to reflect back to so that works except where the foil touches something. It'll sink some heat into the something it touches. Again, it's what fits, it's about all that fits, so use it.
Aerogel is only r15 and it's the best in the world and lab and experimental only.

To reach the rfactor touted it requires three layers with a 4 inch air gap between them, a roof and a ceiling.


I'd use it because it's all that will fit in there, but you're off by a factor of 12 or so on what it the rfactor does.

I use something similar to make a waterproof envelope for the refractory cloth I use for insulation.
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Below is a link to most of my modifications either accomplished or pending.
https://www.thorforums.com/forums/f2...n-18996-3.html

Click on my pictures then click the pop-up for a full screen zoomable picture.
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Old 07-20-2020, 06:59 PM   #6
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Model: 2017 Axis 25.4
State: Arkansas
Posts: 2,606
THOR #12231
I also insulated my Roof AC box two years ago.

IMO painting the cover is NO LONGER need if you insulated the box.

The reason is when I checked my AC unit last year in full afternoon sun the Black cover was hot to the touch but the insulated part under the cover was cool to the touch.

But I guess it could not hurt to paint it white - esp if you like that look or if your black cover looks old.

I like the black color of mine and I use 303 on my roof / vent / AC covers 2x a year so they look like new.
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2017 Axis / 25.4: Big Foot Levelers, Aims 1200 Watt inverter, Ceramic Window Tint, Full River AGM 6V batteries, Front Hellwig Sway bar / Rear Track Arm, Safe T Plus Steering Stabilizer, PD 4655 converter, Hard Wired Surge Guard, WEboost + WiFi Ranger, LED Headlights/Driving lights, TPMS, Surge tank, Tornado flush, Viair Compressor
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Old 07-22-2020, 04:55 AM   #7
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Model: Vegas 24.1
State: Washington
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THOR #10717
Just finished it. Took about 30 minutes. Wrapped it like a gift.
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Old 07-22-2020, 11:36 AM   #8
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Model: 2020 Magnitude SV34
State: Florida
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THOR #12751
I did my two units the same way this spring. It does seem to help.

When we were camping this weekend and it was in the 90's, I was getting temps out of the unit in the 50's and at night in the upper 40's.
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Old 07-22-2020, 07:39 PM   #9
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Model: Chateau 31L
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THOR #12189
The OP cites a squirrel cage fan but I'm seeing fan blades to the condenser.

Is the squirrel cage inside the housing on the other side of the motor? Could or would you go lighter, say a thicker Reflectix?

And how do you access the insulation on the inside of the housing to beef it up or change it out?

Thanks
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Old 07-31-2020, 03:41 PM   #10
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Brand: Thor Motor Coach
Model: Vegas 24.1
State: Washington
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THOR #10717
Quote:
Originally Posted by The_Breeze View Post
The OP cites a squirrel cage fan but I'm seeing fan blades to the condenser.

Is the squirrel cage inside the housing on the other side of the motor? Could or would you go lighter, say a thicker Reflectix?

And how do you access the insulation on the inside of the housing to beef it up or change it out?

Thanks
The OP might be wrong about the fan- i saw a normal bladed fan.
I did not add insuliation inside the roof. I am sure someone has done it though.
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Old 08-01-2020, 11:49 PM   #11
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Model: hurricane 34J
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THOR #19488
can anyone point me to in stock stuff on amazon?


i see nothing currently available that will work.


thanks
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Old 08-02-2020, 01:40 AM   #12
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Brand: Thor Motor Coach
Model: Citation
State: Texas
Posts: 393
THOR #8139
Quote:
Originally Posted by Long & Winding road View Post
I also insulated my Roof AC box two years ago.

IMO painting the cover is NO LONGER need if you insulated the box.

The reason is when I checked my AC unit last year in full afternoon sun the Black cover was hot to the touch but the insulated part under the cover was cool to the touch.

But I guess it could not hurt to paint it white - esp if you like that look or if your black cover looks old.

I like the black color of mine and I use 303 on my roof / vent / AC covers 2x a year so they look like new.

Several of us have made a few mods to our AC's, check post #172 of this thread by Long & Winding road.
https://www.thorforums.com/forums/f2...ice-12980.html
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Old 08-04-2020, 07:09 AM   #13
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State: Arkansas
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THOR #19565
Have you guys seen any difference in ac performance as a result?
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Old 08-04-2020, 11:30 AM   #14
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Brand: Thor Motor Coach
Model: 2020 Magnitude SV34
State: Florida
Posts: 1,395
THOR #12751
Quote:
Originally Posted by t0lbert View Post
can anyone point me to in stock stuff on amazon?


i see nothing currently available that will work.


thanks

This is what I used and got it from Lowes....

https://www.lowes.com/pd/Frost-King-...lation/1081449


I also added foam pipe insulation to the output line of the compressor....

https://www.lowes.com/pd/Frost-King-...lation/3132405


Between adding the insulation to the roof unit, trimming the styrofoam ceiling insulation in the vents and using duct tape to better seal the divider in the plenum, I am happy with the performance of my two A/C units.

I also use Weathertech Sun Shades for the cab and on very hot days I lower the blinds and pull the curtain across the cab-over area.

Last weekend we had a sport with no shade and temps were ~87 - 90. The A/C's had no problem keeping the coach in the 70's.
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Old 08-04-2020, 06:46 PM   #15
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Brand: Thor Motor Coach
Model: Citation
State: Texas
Posts: 393
THOR #8139
Quote:
Originally Posted by bojanlora View Post
Have you guys seen any difference in ac performance as a result?
I measured the air speed at the vents before and after the mods (looking for pictures) 1+ mph gain.
Apples to apples measuring the temperature was harder, time of day, clouds, outside and inside temperatures have to be close before and after.
Doing the air flow mod (it was a mess) at the return made the biggest temperature change, a couple of *'s at the vents with the outside temp going up. We have a dometic ac so the roof coil already has styrofoam insulation.

However
Anytime the outside is going to get over 85 we have a portable ac we place between the front seats, vent out the drive window and powered externally to the 20amp campground.
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