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Old 08-02-2004, 08:59 AM   #1
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Roof-Top AC Maintenance

I just purchased a used 13,500 btu unit for my bus. I have never owned one before and was hoping someone could give me some helpful information on preventative maintenance, any installation advice, or problems you have had with yours that I may be able to prevent. I just got it off of e-bay and have not received it yet. I assume it will need coolant but what kind and when does it need changed or checked?
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Old 08-02-2004, 03:39 PM   #2
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Most of the ones I have seen were sealed and did not have a place to put in freon, but there are "taps" available at AC places.
I don't know of they are R12 or R22.
On most cars, you can retrofit R134 into the R12 systems with little or no changes besides an adapter to allow the R134 fill station to attach.
Just make sure you have a solid place to mount and reinforce it a little.
They fit into a standard 14 X 14 vent hole.
On mine, I just cut a 14 x 14 home in top, then in the ceiling and put walmanized 2x4 pieces ripped to fit between the roof and ceiling.
The AC mounts by just sitting it over the hole, then attaching the bottom plate with long all thread bolts sandwitching the roof between the two.
There is a foam gasket on the bottom of the top unit to seal from the weather.
You will need wires for your thermostat, 12V DC to supply power to the thermostat control board and 120V AC to actually run the unit.
If you need more info, after you get the unit, let us know what model it is.
If it is a Coleman, I can help on the pinouts on the wiring.
1976 International Wayne - ON THE ROAD!!
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Old 08-02-2004, 03:49 PM   #3
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I often wondered how I would get the 120 power up to there while having it look good. Did you run it through the two roof pieces or is it visible from the inside or outside.
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Old 08-02-2004, 06:51 PM   #4
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First, I cut the 14 x 14 hole carefully avoiding structural members.
On my bus, there is a stringer that runs from front to back right down the center so the hole is off center to the right side to clear the stringer and between the ribs that run side to side.
I had the inside ceiling loose at the edges to push the 1 1/2 sheet foam into the void between the frame members.
While I had it down, I ran the thermostat wire, the 12VDC wire and the 120VAC between the roof and ceiling, down the wall, under the floor and then to the breaker box location for the 12V and 120V.
The thermostat control wire goes over to the thermostat mounted on the right hand wall between the two seats on that side.
It is about 18 inches down the wall and controls the on/off, fan speed and temperature.
Then I framed between the roof sheetmetal and the ceiling sheet metal with walmonized 2 x 4s ripped to 1 5/8 inches as that was the distance between the two pieces of metal.
I drilled a hole in the one on the right side as that is the side that the thermostat and power wires are on the AC unit and left them dangling down about 2' to make sure I had enough slack.
Then, I placed the AC unit on the roof over the hole and got inside and centered it over the hole.
After it was bolted down, I connected the wires, then put on the trim on the inside.
You do have to have all 3 wires because the 12V is what the control board runs on that controls the AC.
I bought 6 conductor wire for the run from the AC to the thermostat, but only used 4 of them and have a couple of extras in case one gets cut or something.

Hope this helps!
1976 International Wayne - ON THE ROAD!!
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