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Old 12-15-2008, 06:49 AM   #1
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I am hoping that someone with ventilation experience will be able to comment on my proposed ventilation plan. The more I think about the possible solutions the more variables seem to play.

Like John Canfield, I think my exterior electric compartment which houses my Dimension inverter/converter, transfer switch, Surge Guard unit, and Allison ECU runs very hot, especially during the summer. I would like to move the cooler air from the MH interior into the outside electrical compartment to reduce the temperature and maintain a positive pressure to replace the hotter air with cooler air. I am anticipating enough air leakage that there would not be a pressure build up and replacement air would come from house leakage (windows doors vents.)

With John C’s plan in mind HERE
I went to our 2004 Journey 36G and opened the cover of the interior electrical space located underneath the foot-end of the bed. The 36G design is different then John’s MH. The inside electrical compartment is not located over the outside electrical compartment. But there is already an open electrical wiring trough between the interior and external electrical spaces. The A/C wiring connecting the Dimensions unit and the house circuit breakers mounted in the bed base runs in this trough.

One aside. Apparently when the door of the outside electrical compartment is open and the AC is running then hot air must be drawn from outside through the outside electrical compartment, up the electrical trough, through the inside electrical space, through the vent mounted at the end of the cabinet and into the AC return. I don’t suppose it is a lot of air but I have to think it is like running the AC with a window open. The AC unit has to be working harder and taking longer to reach demand temperature. Even so, the AC unit can freeze us out of there. Hm… another project.

So my question is do I need to install a 3” or 4” duct to move cooler MH air into the exterior electrical space or can I just use the existing electrical trough as an air duct?

To use the existing electrical trough as an air duct I thought of installing an axial 12VDC fan as physically large as possible in front of the existing vent. The fan would push the air to the outside electrical compartment. With the fan continually pushing it seems to me this would cause a positive pressure throughout the entire space (interior electrical, electrical trough, exterior electrical space) preventing air from rising back. However, I was not able to find a 12VDC axial fan large enough to push air to the exterior electrical compartment. The fans that I found were for cabinet cooling. But I did think of the Fan-Tastic Vent product called Endless Breeze. This is a 13” square rotary fan (without legs) x 3” deep with ten 12” blades that provides 900 CFM drawing 3 amps. There are three operating speeds. I spoke with Fan-Tastic Vent and they believe their product would produce the desired results.

Otherwise, I can install an inline blower and blow cooler MH interior air into the outside electrical compartment via a duct. The blower intake would be installed adjacent to the existing interior vent. The duct would be attached to the blower exhaust and installed through the wiring electrical trough down into the outside electrical compartment.

This inline blower plan should accomplish my goal to lower the electrical compartment temperature. However, with the duct installed through one of the odd sized available openings into the outside electrical compartment I do not see how positive pressure can be established. Won’t air be able to circulate back through the various trough opening in to the space above?

If the duct is feasible solution, the 3” duct will be easier to install. I might not be able to snake in the 4” duct. Since this is a 6’ run will the 3” duct do the job? A 4” blower will draw 12 amps; the 3” blower draws 6” amps.

Photo1 shows the exterior of the interior electrical space where I will mount fan and duct (if used). This space is accessed with the bed raised.


Photo2 shows the same space with its cover removed. The back of the A/C electrical box is shown. It is below that box where the largest opening and space is available to install the duct.


Photo3 shows the interior vent that is already installed which I assume is meant to keep this enclosed interior electrical space from overheating.


Photo4 The floor opening shown into the electrical trough space has always been opened and I am assuming it was meant to be that way. With the electrical compartment door opened outside and the MH entrance door opened a nice draft of air can be felt.

Hot air rises and cool air sinks. So with the exterior electrical compartment door closed and the interior space sealed off except for the vent shown in photo 3 is the rising hot air adding heat to this enclosed electrical space located in the bed room or is the cooler air moving down naturally from the MH interior through the vent to help cool off both the interior and exterior electrical compartment? I think it’s heating it up because of the heat load provided by the running engine.

Note you can see the exterior in the upper right corner of the floor opening.


Photo 5 the electrical cable stored in the electrical compartment can be seen.


Photo 6 is taken from the outside looking in and illustrates proximity.


Photo 7 shows the opening where I intend to install the duct (if used) behind the AC electrical box.


Photo 8 shows the snake that I will use to pull the duct (if used) and electrical wiring to run blower or fan and proximity.



I think I prefer the Endless Breeze fan type solution.
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Old 12-15-2008, 06:49 AM   #2
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I am hoping that someone with ventilation experience will be able to comment on my proposed ventilation plan. The more I think about the possible solutions the more variables seem to play.

Like John Canfield, I think my exterior electric compartment which houses my Dimension inverter/converter, transfer switch, Surge Guard unit, and Allison ECU runs very hot, especially during the summer. I would like to move the cooler air from the MH interior into the outside electrical compartment to reduce the temperature and maintain a positive pressure to replace the hotter air with cooler air. I am anticipating enough air leakage that there would not be a pressure build up and replacement air would come from house leakage (windows doors vents.)

With John C’s plan in mind HERE
I went to our 2004 Journey 36G and opened the cover of the interior electrical space located underneath the foot-end of the bed. The 36G design is different then John’s MH. The inside electrical compartment is not located over the outside electrical compartment. But there is already an open electrical wiring trough between the interior and external electrical spaces. The A/C wiring connecting the Dimensions unit and the house circuit breakers mounted in the bed base runs in this trough.

One aside. Apparently when the door of the outside electrical compartment is open and the AC is running then hot air must be drawn from outside through the outside electrical compartment, up the electrical trough, through the inside electrical space, through the vent mounted at the end of the cabinet and into the AC return. I don’t suppose it is a lot of air but I have to think it is like running the AC with a window open. The AC unit has to be working harder and taking longer to reach demand temperature. Even so, the AC unit can freeze us out of there. Hm… another project.

So my question is do I need to install a 3” or 4” duct to move cooler MH air into the exterior electrical space or can I just use the existing electrical trough as an air duct?

To use the existing electrical trough as an air duct I thought of installing an axial 12VDC fan as physically large as possible in front of the existing vent. The fan would push the air to the outside electrical compartment. With the fan continually pushing it seems to me this would cause a positive pressure throughout the entire space (interior electrical, electrical trough, exterior electrical space) preventing air from rising back. However, I was not able to find a 12VDC axial fan large enough to push air to the exterior electrical compartment. The fans that I found were for cabinet cooling. But I did think of the Fan-Tastic Vent product called Endless Breeze. This is a 13” square rotary fan (without legs) x 3” deep with ten 12” blades that provides 900 CFM drawing 3 amps. There are three operating speeds. I spoke with Fan-Tastic Vent and they believe their product would produce the desired results.

Otherwise, I can install an inline blower and blow cooler MH interior air into the outside electrical compartment via a duct. The blower intake would be installed adjacent to the existing interior vent. The duct would be attached to the blower exhaust and installed through the wiring electrical trough down into the outside electrical compartment.

This inline blower plan should accomplish my goal to lower the electrical compartment temperature. However, with the duct installed through one of the odd sized available openings into the outside electrical compartment I do not see how positive pressure can be established. Won’t air be able to circulate back through the various trough opening in to the space above?

If the duct is feasible solution, the 3” duct will be easier to install. I might not be able to snake in the 4” duct. Since this is a 6’ run will the 3” duct do the job? A 4” blower will draw 12 amps; the 3” blower draws 6” amps.

Photo1 shows the exterior of the interior electrical space where I will mount fan and duct (if used). This space is accessed with the bed raised.


Photo2 shows the same space with its cover removed. The back of the A/C electrical box is shown. It is below that box where the largest opening and space is available to install the duct.


Photo3 shows the interior vent that is already installed which I assume is meant to keep this enclosed interior electrical space from overheating.


Photo4 The floor opening shown into the electrical trough space has always been opened and I am assuming it was meant to be that way. With the electrical compartment door opened outside and the MH entrance door opened a nice draft of air can be felt.

Hot air rises and cool air sinks. So with the exterior electrical compartment door closed and the interior space sealed off except for the vent shown in photo 3 is the rising hot air adding heat to this enclosed electrical space located in the bed room or is the cooler air moving down naturally from the MH interior through the vent to help cool off both the interior and exterior electrical compartment? I think it’s heating it up because of the heat load provided by the running engine.

Note you can see the exterior in the upper right corner of the floor opening.


Photo 5 the electrical cable stored in the electrical compartment can be seen.


Photo 6 is taken from the outside looking in and illustrates proximity.


Photo 7 shows the opening where I intend to install the duct (if used) behind the AC electrical box.


Photo 8 shows the snake that I will use to pull the duct (if used) and electrical wiring to run blower or fan and proximity.



I think I prefer the Endless Breeze fan type solution.
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Old 12-15-2008, 07:05 AM   #3
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Interesting. While I am no HVAC expert, why wouldn't a thermostatically-controled 12 V fan installed somewhere in the lower electrical compartment work? Thinking of how my rig is configured (looks the same), I would try to exhaust the hot air out of the back of the compartment (just to the rear of where the power cord is stored). The fan should pull cooler air thru that vent in the bed enclosure, down thru the lower compartment and out.
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Old 12-15-2008, 07:17 AM   #4
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Yes, that is an idea I have thought of. Not sure if I can install a fan in that space and keep electrical compartment dry. Also, wall space is a premium. See photo below. I probably need to go back and check it out again.

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Old 12-15-2008, 11:39 AM   #5
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My eletrical compartment would really get hot after a day on the road. I started looking around to find out why. What I found was that the muffler was close to to the back of the compartment. When it was hot the back of the compartment was really hot. I got a peace of heavy sheet metal and mounted it to the back of the box with about a inch of air space between the plate and the back wall. Did that make a differents. Much cooler.If you add the fan to push cool air in, the air going in needs to vent out some where are you will not get moving air. Just pressurise it.For me mine has been fine, ever since the modification. Food for thought.
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Old 12-15-2008, 12:34 PM   #6
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Thanks Randy. Yes, I agree about the BIG heat coming from the muffler which sits just behind the electrical compartment. I had not thought of trying to add a heat shield. I'll have to look under and see if I can find away to safely add one. Hate for any of my stuff to fall off and become a road missile. This project just gets more and more interesting. SteveG
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Old 12-15-2008, 01:54 PM   #7
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I've looked for ways to cool down that outside electrical compartment for several years, but it seems any kind of ventilation from outside would just allow more engine odor getting into the coach than is already doing. Three years ago while at Forest City and telling them of the constant engine odor in the bedroom they claimed to have found and sealed a couple of holes in that compartment. This, which I would assume will make it even hotter in there. With the exhaust pipe at that rear corner, I have been trying to seal around that compartment door with weather striping trying to eliminate any engine odor from being drawn in and up into the bedroom.
This all sounds like a no-win situation for the owner.

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Old 12-15-2008, 02:20 PM   #8
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Wagonmaster2, So far I have only had engine odor one time and that was connected to FreightLiner's muffler exhaust line joint slippage recall. FL shoved the exhaust line joint back in place and refastened and so far no more odor.

But if there is seal leakage allowing odors they should be repaired. Then possibly my postive pressure ventilation plan might also help. With enough positive pressure outside air should not be able to intrude into the compartment and it, hopefully, will reduce the compartment's temp. At least that's my theory!

Once I install a ventilation system I'll let you know the results. Hopefully some others have done this and will be able to add to the plan. SteveG
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Old 12-16-2008, 07:51 AM   #9
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Steve, Like you and John I had concerns about the temperatures developing in that electrical compartment. This past spring I installed a 4”, high displacement fan on the wall of the compartment facing the engine. It pulls the air out of the electrical compartment and exhausts it outside between a baffle plate in the engine compartment and the electrical compartment wall. I installed it with a three way switch and thermal switch that closes I believe at 96 degrees and does not open up until temperatures are down to 88 degrees. So far it seems to be doing the trick. It is pulling outside air into the compartment through the existing cable run that is open to the outside somewhere. The three way switch allows me to switch the fan off – always on – automatic (via thermal). So far I have not had a need to take it off the automatic (thermal) setting, so that might have been a design overkill.

I installed a remote temperature sensor down there this summer and with temperature running around a 100 degrees outside, the compartment ran about 6-8 degrees above that ambient temperature with the fan constantly running. Prior to making the fan modification I contacted Dimensions regarding their temperature specs. and I was told that the unit will enter degradation mode (reduce capacity and as such reducing heat output) when temperatures exceed 108 degrees and has a thermal shutdown at around a 140 degrees. They wouldn’t commit to a “don’t exceed this temperature” statement.

This spring I also had to replace that “famous Trombetta solenoid” that parallels the battery sets while driving. It exists in the same electrical compartment and its life expectancy was probable not helped by the high temperatures that existed in this compartment in the past.

Last year I had already found and consequently closed up the cable route from the lower compartment to the area under our bed (yep hot air and road grime coming in). It seems that that cable run is also open to the outside somewhere. In any case fixing that outside air exposure and insulating the engine compartment cover with fiberglass bats has made a big difference in keeping the bedroom area cool while traveling and cooling the coach down further when stopped with a hot engine. It also stays clean under the bed now. (My better half is doing much better now with her allergy problems).
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Old 12-16-2008, 11:19 AM   #10
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Harry, thanks so much for the information. Smlranger also suggested a fan mounted in the electrical compartment. And Randy said adding a heat shield worked very well for him. So I went to the MH today to refresh my memory.

My muffler runs almost the full length of the electrical compartment. The space between the muffler and the back of the electrical compartment is one inch or less. With such a small space, I wasn’t able to figure how I could fit in a heat shield. So my space must be shaped different then yours and Randy’s? The remaining space along that back wall is taken up by the surge guard I installed.

The end wall (facing the back of the MH) looks available from the outside. But on the inside of the electrical compartment there is a false wall and then mounted behind the false wall on the actual end wall is the Allison ECU and the Tow Controller and some other junction box. The false wall protects this equipment and contains all the wiring that feeds these components. If I get real ambitious I may replace the false wall with an open metal mesh to provide better circulation. But as of right now I am not yet willing to risk using that space for a fan mount and have something go wrong as all the components are vital.

I agree with you about the cable run being open somewhere else. I think in the 36G it extends to the front maybe as far as the gray and black tanks. If I use a positive pressure fan maybe I’ll discover where when I open and close the various bay doors.

Since you closed off the cable trough openings have you noticed any significant heat building up in the enclosed space behind the AC electrical boxes mounted at the base of the bed? How did you close it off, with expanding foam? The one opening has no cables so that one will be easy. The other has cables and will be more difficult. I was originally thinking that by leaving that opening in place I would either push or pull heat out of that space as well. It might also be helpful during that initial engine cool down period.

Good idea about insulating the engine cover. Would you please explain how you accomplished that; size of batting and how you installed them?

Thanks again for the input. My guessing at all this and then going out and purchasing and installing equipment that can’t get the job done will be disappointing. So your success is something I can build on.
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Old 12-17-2008, 07:07 AM   #11
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Steve, on my muffler cleareance I only had a inch to work with. I cut me some 5/8" shims and put them between the back wall and the plate. There is a product called Dynamat thermo - acoustic foam. You can get it from 1/8" to 1/2" thick. I use it for the floor boards on the street rods I build to keep the exhaust heat down. Works great. www.eastwood.com use key word dynmat you will see what I'm talking about.I'm getting ready to do my compartment with 1/4". The hole thing with the muffler being that close to the boxs is a bad design. The way I look at it, is you got to get that muuffler heat in the boxs down. I don't think you can blow enought air in to the boxs to do that.With the heat shield I don't that. There is one more thing to do and that,s put a different muffler. Like Arrows 5050 5" in and 5" out. That will be my nexts move.
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Old 12-17-2008, 05:43 PM   #12
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Randy, thanks for the information. I agree with you about the heat. I think in the long term it will do in the equipment. Unfortunately I have zero experience in heat shield work. But it makes sense to try to first reduce the heat and then if necessary let a fan ventilate the balance of the heat.

How did you attach the shims to the heat shield plate and the plate to the wall in such a small space?

Placing the Dynamat on the interior walls of the electrical compartment might be a problem for me. As you can see from the last photo showing the electrical compartment I could place it on the floor and the vertical wall where the 50 amp electrical cables are attached. I don’t think I can fit any in the space behind the false wall where the Towing Controller and Allison ECU are located. But I am assuming some Dynamat would be better then none? Can you mount the Dynamat then mount equipment on top of the Dynamat fastening through it to the metal wall?
Thanks, Steve
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Old 12-18-2008, 04:20 AM   #13
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My heatshield is 24"l x 11"h with a 2 1/2" lip. I had the plate bent 90 degree that gave me a 2 1/2" x 2 1/2" lip . I put the plate where I wanted it with the gap and drilled my holes threw the lip into the bottom of the boxs and bolted it in. then I drilled the top holes threw the back wall and plate and put my bolts threw with my 5/8"shim. I did mine myself. It would have been easier if I had a second hand. A sheetmetal shop, are a welding shop can fixs up your plate. It's my seem like alot of work, but it's not. Well worth the work. You can mount your equiment on top of the Dynamat. The mine wall to do is the back wall. If they would put a engineer in a rv for a year and have him vist with RV's we would have nothing to modify.
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Old 12-18-2008, 05:24 PM   #14
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Randy, I’ve mixed feelings about my “projects” list. It’s definitely kind of a hobby rebuilding the parts that they didn’t, so I enjoy it in some ways, but in other ways it would have been nice if had thought the heat thing through. Anyway, I took a trip out to the MH today and did the measuring. The one piece that I think I can get between the muffler and the box is also 23” x 11” and it will mount the 23” vertical. Based on the way you did it I think I can duplicate it.

Is there any reason to place a heat shield over the end of the cabinet? I am assuming that air flow across the bottom cools off and carries away the heat.

I checked out Dynamat and found even a more expensive product called Dynashield. Expensive stuff. I wrote them an e-mail describing my problem to see what they might recommend. Thanks, Steve
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Old 12-19-2008, 03:05 AM   #15
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Steve, there is really no reason to worry about the end of the box. Dynashield is expensive.You do have a point on redoing thing. It does keep us busy. I,m allway changing things. Some of the best changes was to my battery boxs, A/C unit and the iceboxs. I got a new problem too work on and that the 3M film on front of my coach is cracking.I got to find out if anyone have that problem.
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Old 12-23-2008, 01:04 PM   #16
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I wrote the following e-mail to the Dynamat company:
I have a Motor Home that has an electrical compartment which houses an inverter/charger, Allison transmission ECU, and a power surge guard. The back side of this compartment sits up next to the muffler that serves our CAT 330 HP diesel engine. Because of the proximity to the muffler when the engine is running the electrical compartment stays very hot. The muffler sits about 1” from the back of the electrical compartment and it is only possible to mount a metal heat shield for 11” of the 23” wide wall in that small space.

Can Dynamat be mounted on the interior of the electrical compartment walls and floor to help lower the compartment temperature?

The following is the reply:
Thank you for your interest in Dynamat. In the compartment, we would recommend a two product solution. First, apply Dynamat Xtreme (1/8”) to the wall where the muffler is located on the other side. Over Dynamat, install our ˝” thick Dynaliner. The combination will deliver excellent thermal results. Please let us know if you have any additional questions. Technical Department, Dynamic Control of North America, Inc

My plan is still developing. SteveG
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