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Old 04-15-2018, 03:44 PM   #1
Junior Member
Brand: Thor Motor Coach
Model: ACE 29.2
State: Virginia
Posts: 22
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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Jim Jacobs is offline   Reply With Quote
Old 04-17-2018, 04:17 PM   #2
Senior Member
Brand: Thor Motor Coach
Model: 2013 31L
State: Florida
Posts: 1,973
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....


blw2 is offline   Reply With Quote
Old 04-17-2018, 05:47 PM   #3
Junior Member
Brand: Thor Motor Coach
Model: ACE 29.2
State: Virginia
Posts: 22
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.
Jim Jacobs is offline   Reply With Quote

coleman mach 3, insulation, rooftop ac

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