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Author Topic: MC-9 Roof a/c  (Read 2674 times)
cpschevy
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« on: May 05, 2007, 10:24:02 PM »

I am looking at the carrier low profile ducted units (so my bus will fit out of my shop door when im done!)any ideas on sizing and how many i need?I see everyone putting at least 3 13,500 btu units on but most people i talk to say they never use more than 2 at a time! Do i really need 3 or can 2 keep up? any input or recomendations would be great!        Thanks Chris
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Nick Badame Refrig/ACC
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« Reply #1 on: May 06, 2007, 05:54:29 AM »

Hi Chris,

Welcome!

First, tell us what bus you have, is it a saudi? and how well you insulated it. Then it will come down to, how cool do you like it inside, what climate do you live in? etc.

Theese factors are what you should concider before making your decision.

Good Luck
Nick-
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« Reply #2 on: May 06, 2007, 06:01:13 AM »

We have 2 on our MC7 & find they will not do the job when it is very hot or when driving into the sun; however, I found out the PO did not change the original insulation when the conversion was done so more insulation would help.

TOM
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« Reply #3 on: May 06, 2007, 07:17:26 AM »

As Nick and JJRbus mentioned there are several variables that have to be considered. What is YOUR comfort range? We live in South Florida and keep our ACs (both home and bus) set at 80 degrees. Where will you be using your bus? Big difference maninting your comfort zone in Florida or Michigan.  How well is your bus insulated? We have 2" spray foam in walls and about 5" in ceiling. How many windows and are they single or dual pane? Do you have awnings over your windows? What color is your bus? We did a test a few years ago using a laser temperature gun. In the middle of the afternoon in July, west side of 2 buses. Our white bus was 113 degrees. A friends dark metallic green bus was 140 degrees. All that extra heat that is absorbed has to be removed by the AC system.  We keep our bus comfortable with 1 RVP (formerly Coleman) basement unit that is rated for 24,500 BTU. This unit was installed using ducts sized per the manufacturers recommendations.  Jack
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« Reply #4 on: May 06, 2007, 07:18:33 PM »

My MC9 has two Dometic heat pumps that do a good job of cooling (and heating) the bus.  Like Jack says, what's comfy for me may not be for another.   I've also got foam ceiling and walls.  Makes big difference.
The Dometics are low profile...about 9"?  They are low. 
Anyway, I've got the same problem with building clearance.  If you are close, and that must be the situation, this is a good time to add leveling capacity to your bus.  Then the choice of ACs won't be limited to low profile units...although, the low profile units look better than the tall ACS. 
Create a way to dump the air from  the drive and steering axle (while keeping the air system up) and the bus will lose from 5 to 7 inches.  I would recommend moving only enough to get the bus into the building when the airbags are flat.  I poured a concrete pad for that purpose.  No jarring. 
Best, JR

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« Reply #5 on: May 06, 2007, 07:53:08 PM »

I have 3-13,500 roof tops that are spaced- front, near enough to the drivers seat that I can feel it. Middle of the bus and rear right over the rear bed.  Mostly use the two front and kick on the rear when over 100 degrees (which when it happens, am very glad it is there!).  Plus you then have a built in redundancy if one gives out-although in 12 years hasn't had anything go wrong with them.  If I were to do it again, would most likely use the 15,000btu Dometic Penquin, with two in the middle and front position.  Rear always seems to cool easily once the engine heat is gone.  Good LUck, TomC
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« Reply #6 on: May 06, 2007, 08:35:19 PM »

I like the recovery of the condensate evaporation on the carrier.

I bought my bus with 2 Colmans already installed.  They are also in the Emergency Hatches.  I recommend keeping the hatches also if possible.  you'll miss them if they're gone.  also offset to the side might buy you a couple inches. 

GET SLOW SPEED FAN!!!!!!!


I have white paint on mine for cooling purposes.

if you have the floor up there is a lot of room under there for duct if you want to run a basement air

let us know what you come up with Cool



« Last Edit: May 06, 2007, 09:34:09 PM by NewbeeMC9 » Logged

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« Reply #7 on: May 06, 2007, 09:23:16 PM »

will to everybody, thanks for your input !   what I have is a 1983 mc-9 rite now it is in the wall framing stage and i am putting 1  3/4 inches of polycynurate sheet insulation by Dow in the walls.that should give me 11.5 r-value according to the tech at dow. than i am putting 4 inches in the ceiling which = around 22 r-value the floor will probably be the same.the color is going to be white with grafics on the sides.I live in Idaho and the bus will be for camping and also road trips to different states . temps around here are around 100 degrees in the valley where i live and 80 to 90 in the mountains where we camp.the windows are all thermo pane except the winshields of coarse and there are  windows. when i first decided to build a bus i wanted a basement air but a friend of mine that sells motorhomes told me that everybody was complaining that on 100 degree days or when parked on asphalt they would not keep up. and when we borrowed our friends 36 foot winabago it did that  exact thing. itwould only get down to 85 on a 100 degree day! I like a comfortable 75 to 78 degrees when we are travelling.
                                                                               thanks everybody      Chris
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« Reply #8 on: May 06, 2007, 09:44:13 PM »



I also have some of this mixed into the roof paint.

http://www.hytechsales.com/insulating_paint_additives.html

hard to say but i think it helps.

my bus stock insulation and single panes , it only get into the 90's inside when sitting in the sun closed up.
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« Reply #9 on: May 06, 2007, 11:35:10 PM »

Chris, Give me a call MCI 9 Caldwell 870 4342
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« Reply #10 on: May 20, 2007, 10:03:32 PM »

My MCI-9 has two roof airs.  Currently in Phoenix, temp hit 100 today.   Three days ago the bedroom A/C stop cooling.   Cry

Can't get in to a shop till Wednesday Cry  Cry

Wish I had three overheads..... Huh

Bill
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« Reply #11 on: May 21, 2007, 10:55:50 AM »

Bill, go to the local discount RV store and buy another AC.   May be cheaper than paying to have your old unit repaired.  All you need  is a farm tractor with a loader (campground probably has several).  Set the AC unit right in place.  Easy to replace.
You ruled out 110V and 12V (if necessary) problems?
Use the old unit as a spare...if it's repairable.
Good luck, JR
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JR Lynch , Charlotte, NC
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« Reply #12 on: May 21, 2007, 11:04:51 AM »

The two 13.5s in my 4104 won't keep it cool in very hot sunny conditions, so sun and it is very comfortable.

Fortunately for us the PO installed two folding doors, one separates the bedroom and the other separates the kitchen area from the front. We close both these doors, crack open some windows in the closed areas and the one AC in the front keeps it comfortable, not really cool, but comfortable. I also cut a hole in the front housing so the air blows straight down, no turns to slow it down. This really helps. I've never had to turn it to HI COOL since cutting the hole.
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« Reply #13 on: May 21, 2007, 11:19:30 AM »

All you need  is a farm tractor with a loader (campground probably has several). 

    Worst case scenario, if no tractor or machine to lift the AC to the roof, I have installed several Roof ACs by placing an extension ladder against the side of the bus, placing the AC (still boxed in the shipping crate) against the ladder. Put a strap tightly around the AC  box, attach a rope and from the roof of the bus, pull the AC up the ladder onto the roof. The old AC is then placed in the box and lowered the same way.
    Of course, IF you have a tractor available it is much easier.  Jack
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« Reply #14 on: May 21, 2007, 11:36:00 AM »

Jack mentions something that is important...the sealing gasket is typically attached to the AC unit.  Never slide an AC around on the gasket.  Once out of the box, it must be picked up and placed in location.  Once on the roof, one person should be able to handle an AC.  You will need a helper inside to locate the retaining bolts. 
JR
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JR Lynch , Charlotte, NC
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« Reply #15 on: May 21, 2007, 11:58:22 AM »

All you need  is a farm tractor with a loader (campground probably has several). 

    Worst case scenario, if no tractor or machine to lift the AC to the roof, I have installed several Roof ACs by placing an extension ladder against the side of the bus, placing the AC (still boxed in the shipping crate) against the ladder. Put a strap tightly around the AC  box, attach a rope and from the roof of the bus, pull the AC up the ladder onto the roof. The old AC is then placed in the box and lowered the same way.
    Of course, IF you have a tractor available it is much easier.  Jack

If the escape hatches are still available (i.e. not framed for the A/C itself), you might be able to get the unit through the opening.  That's how we got the full-sized Carrier 15k on my MC-8.  It's definitely easier to do this with two people; I'm not sure if I could have done it by myself.

David
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« Reply #16 on: May 21, 2007, 09:54:30 PM »

JR, and everyone,

The unit runs, just does not cool.  Guess I should open it up and see if it something simple.

Thanks,

Bill
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« Reply #17 on: May 22, 2007, 08:34:48 AM »

I first tried the loader method, but the flex of the tires allowed it to move back and forth by 4 or 5 inches.  My coach is tall enough, I needed to get the loader close so I could grab the air cond unit.  The bucket bounced lightly off my drip rails.  Not good.

The others I put up using Jack's method or variant.  Worked well.  Those units are not that heavy and one guy can manhandle them up with out too much trouble.
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« Reply #18 on: May 22, 2007, 08:40:09 AM »

How old it the unit?  If iut runs but does not cool, this usually means the freon has leaked out.  Jack
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« Reply #19 on: May 22, 2007, 08:48:00 AM »

JR, and everyone,

The unit runs, just does not cool.  Guess I should open it up and see if it something simple.

Thanks,

Bill

Bill,

Just a suggestion here,

When I was working at the campground I had a lot of rental campers to take care of.

One of the major complaints was A/C's not cooling. About 40% of the time the problem turned out to be dust plugging the evap and condenser fins. My fix was to get an air hose on the inside and clean them out. I found that no matter how good the filter was, they always leaked air around and through them.

You might want to try cleaning the unit really well. Oh, and put down a tarp ofer every thing you want to keep clean. It's amazing how much crud will get blown around.

Dallas
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« Reply #20 on: May 22, 2007, 09:31:00 AM »

I used a forklift at a friend's house to install my roof AC units.  He has a little electric forklift with hard tires.

He just parked the lift alongside the roof and came up to help me lift the units into place.
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« Reply #21 on: May 22, 2007, 10:17:16 PM »

Jack,

Not sure how old the unit is.  Will have to call and find out.  My though is that it has lost feon.  That can't cost that much to have it tested and fixed. Does it?

Would be hard for me to replace it and use it for a spare.  Remember, I am a full timer and my company moves me every couple three months.  I would not have any place to store the other unit.

Bill
Currently in Phoenix

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« Reply #22 on: May 22, 2007, 10:34:50 PM »

Considering you can get a new A/C from Camping World for about $550.00, I wouldn't fool around with the old one.  Once you fix this, what will go next?  Good Luck, TomC
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« Reply #23 on: May 23, 2007, 04:11:34 AM »

Bill,
   I replaced a couple roof ACs last summer on travel trailers. One of these, the owner called a local AC company to check and repair her unit. They told her to replace it when she called them. Their experience was that repairs did not last and they had unhappy customers, so they no longer repair them. On both the units I replaced, you could see a lot of corrosion on the aluminum condenser. I think that is probably where the leak was, and there would probably be other leaks in the near future due to the continuing corrosion. I would not consider keeping the old unit as a spare.
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« Reply #24 on: May 23, 2007, 10:28:52 AM »

Guys,

My units are 4-5 years old.

I will clean and check for dust as Dallas recommends.

If that doesn't correct the problem I will replace with a new unit.

Thanks again gentlemen,

Bill
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« Reply #25 on: May 24, 2007, 10:06:37 AM »

Should I replace the entire unit or just the top part?

Thanks Again,

Bill
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« Reply #26 on: May 24, 2007, 01:58:13 PM »


Last one I replaced the  inside piece would not match the new top part. I forget why, but I know we tried and could not get them 2 pieces to work together.  Jack
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« Reply #27 on: May 24, 2007, 03:11:57 PM »

We had one of our roof A/Cs recharged in 1996. I looked up the bill. The only thing that the tech could figure out as the cause of the problem was that our bus sat outside in the extreme cold (-35degrees) the previous winter and the freon leaked out. There was only one HVAC guy that would work on roof A/Cs in our area so we took it to him. He installed two tap valves and recharged the unit and it has worked well ever since. Total charge was $78.81. Remember that was 11 years ago, but a new A/C was about the same price as they are now so I felt it was worth the risk.
Best wishes, Sam 4106
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« Reply #28 on: May 26, 2007, 06:43:30 PM »

Hey Guys,

Replace the rear roof A/C today.   Pretty easy to do, the hard part was getting the unit to the top of the bus, by myself.  I don't recommend this appoarch.

The first try was with a ladder leaning on the bus,  a rope around the unit. Me on top of the bus. Sliding the unit up the ladder.  This "almost" worked.  If the ladder hadn't had a plastic top that the box hung up on, this "may have worked". After trying this a second time, I gave up.   Angry

As luck would have it, there was a stack of hay 25 yards from where I'm parked.  Grin  Loaded the A/C unit back in the car, then stair stepped it to the top of the hay.  Backed up the bus to the hay, the hay was level with the top of the bus.  From this point it was easy to slide the box with new A/C over to the bus.  Smiley

Changing out the unit was easy.

Tomorrow, I will remove from the roof, the old unit. 

Bill

Still in Phoenix
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