June 24, 2018, 03:02:11 AM

Author Topic: Advice two things foam and over road AC  (Read 3216 times)

Offline rkillmon

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Advice two things foam and over road AC
« on: May 13, 2013, 05:42:02 PM »

1. a company that converts buses into RVs stated that they don't use spray foam insulation because it cracks later and causes leaks, is this true? If the bus is gutted, is spray the best?

2. Should you save the AC unit that runs off the bus motor when converting or go with units on the roof? Can the units on the roof be run from the bus engine while driving down the road?[
1976 MCI 5B challenger

Offline Sam 4106

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Re: Advice two things foam and over road AC
« Reply #1 on: May 13, 2013, 06:05:18 PM »

1. That is a very questionable statement. Our MCI 8 conversion was spray foamed about 20 years ago and there are no signs of a leak. Prevost spray foams their new commercial bus roofs and lower walls and their conversion shells completely except the windows. My guess is that the real reason the company that told you they don't use spray foam is because of cost or that they don't have the right equipment to do it.

2. Some folks choose to keep the over the road A/C, others remove it. I have read several times that the over the road A/C is the most expensive maintenance item there is on a commercial bus. If you have the 50DN alternator on your bus, powering a large enough battery bank, and a large enough inverter, you can run a roof air or two from the bus engine. Or, you could run them off your 120VAC generator, if it is large enough, going down the road.

Good luck, Sam
1976 MCI-8TA with 8V92 DDEC II and Allison HT740

Offline TomC

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Re: Advice two things foam and over road AC
« Reply #2 on: May 13, 2013, 09:02:38 PM »
Spray foam should be sprayed with the inside face open so when it cures you can shave it down to the level you want. I think they were referring to when you foam when both walls are in place. I foamed my bus with 2.25" foam and it is still good. Now my truck maybe a different story since the new spray foam isn't as toxic (read as good) as the old fashion type.

You can run a roof top A/C going down the road from the big alternator and an inverter. I don't-I just run my 10kw generator and use two or three of the roof tops. The above mentioned spray foam really works well. I don't have to kick on the third A/C until it is hotter then 105 outside-two cool (13,500btu) just fine going down the road. Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline belfert

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Re: Advice two things foam and over road AC
« Reply #3 on: May 14, 2013, 05:46:41 AM »
My bus has the lower walls and the ceiling spray foamed from the factory.  Not the greatest job as they didn't overfill and then trim it down.  I don't feel like the insulation is all that great, but having a huge windshield and four 3 foot x 4 foot windows up front doesn't help.

Hot applied spray foam can crack and split as it cools.  The rim joists at my house were spray foamed with hot applied foam and it cracked all over the place.  I complained and all they did was came out with a couple cans of foam and filled the cracks.  If you can find someone who does the cold applied spray foam it supposedly won't crack.
Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN

Offline Mike in GA

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Re: Advice two things foam and over road AC
« Reply #4 on: May 14, 2013, 06:44:21 AM »
Spray foam insulation is generally a good idea when your rig is a shell and the inside wall is open, as has been mentioned.
     Make sure any in-wall and in-ceiling wiring is in place first. The two part foam is beneficial because 1) it fills most cavities and tightens the coach, 2) it soundproofs somewhat, 3) it emits no squeaks as you might get with blocks of foam, and 4) it is very good insulation, summer and winter.
     The downside can be the cost and definitely the mess and labor of shaving the excess foam back to riib thickness, so you can add your interior walls and ceiling.
     Just my $.02 worth!
Mike in GA
Past President, Southeast Bus Nuts. Busin' for more than 15 years in a 1985 MC 96a3 with DD 8v92 and a 5 speed Allison c/r.

Offline Uglydog56

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Re: Advice two things foam and over road AC
« Reply #5 on: May 16, 2013, 08:33:26 AM »
It is supposed to add strength too I have heard. My recently departed bus was spray foamed in 1987 and showed no evidence of cracking. It had 3.5" in roof ond 2.5" in walls and with a fan circulating the air you didn't need any ac until it was over 90.
Rick A. Cone
Silverdale, WA
66 Crowny Crown "The Ark"

Offline Gordie Allen

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Re: Advice two things foam and over road AC
« Reply #6 on: May 17, 2013, 07:57:29 PM »
4104.  I bought a two part spray foam kit and covered the ceiling and walls with 1.5" between the ribs, then covered all with a continuous sheet of double bubble foil insulation, taping all the seams. Covering this with 3/8 plywood screwed to the ribs provides a virtual air space between the plywood and the ribs, minimizing heat, and sound conduction - plus adding two layers of radiant reflection between the plywood and the foam.  The plywood is covered with 1/4" foam-backed Naugahyde which adds a little more insulation and sound deadening.

Air conditioning is via two 9000 BTU, 120 volt mini-splits powered by a 1000 amp hr. battery pack, a 300 amp alternator dedicated to that pack only, and a Victron true sine wave inverter .  A second alternator provides power for the two vehicle batteries - starter, lights, heater motors, wipers, etc.  Haven't had it out in 105 degrees, so no report on just how well it performs.
Augusta, MI
1956 4104
DD 671