Are rooftop AC units standardized for mounting?

[urbex]

Picked up an '87 class B several months ago, that ended up having a potentially bad AC unit. Started tear down of the insides for rebuilding and to fix a saggy roof, which I believe will involve removing all the wooden structure to rebuild it.

If the AC does need to be replaced, is the mounting and opening size standard on these things, so I can just rebuild the existing opening and mount a new unit up there later, or is this going to be a case of fully diagnose the AC NOW, and have a new unit on hand to size the opening & framing to?

At this point, I'm not 100% positive that I even want to keep the AC if it is in fact bad, but I would like to keep the option open if I decide to reinstall later on. So I plan on running the 120V wiring up there, and possibly even some heavy gauge wire to prepare in the event I go with a DC powered unit (unlikely, given the price difference, but I'd rather throw $100 of wire up there now than pull a ceiling down later). I also want the framing in place for the same reason - better to have it and not need it....

[urbex]

wa8yxm wrote:

To lean the condenser on a coleman remove 4 Phillips head bolts from top lift off cover peal built up "Crud" off the condenser replace cover and 4 bolts done

I have a feeling this may be part, or even all of my problem. When I first got the van home, I tested all of the appliances (I bought this thing cheap enough that all the appliances could be dead, and I'd still feel like I got a deal on it) Found the AC would turn on, fan started up, and then I could hear the compressor kick in a few seconds later, but it wasn't even beginning to cool down after 30 seconds.

Then I got severely ill, was out of commission for a couple months, and when I started to feel better, I also started demo of the interior...having completely forgotten about the AC issue.

The AC has to come off the roof so I can do the roof/ceiling repairs, and I figure it will be simpler to clean/diagnose on the ground anyways.

[deltabravo]

Standard sized for a 14"x14" roof vent opening.

Easy to install too.

Here's how I installed one

[wa8yxm]

the hole in the roof is a very standard 14 inches square.
however the thickness of the roof and any "Middle" section for Ducting may and I stress MAY be different.. Some replacement units are designed so that does not matter..

One other thing.. Coleman's suck others blow
By that I mean Coleman units draw air in through the condenser (Suck) and blow it out the sides.. Others do it the other way around.. Why is this important?

To lean the condenser on a coleman remove 4 Phillips head bolts from top lift off cover peal built up "Crud" off the condenser replace cover and 4 bolts done

Others remove around a dozen screws an the cover then figure out how to open the inside cover over the condenser may or may not be easy how the fan is in the way of cleaning so you may need to remove it... See the difference.

[RLS7201]

Typical RV ACs sit on the roof on top of a gasket. Maybe a shim and 2 gaskets for your height?

Richard

[urbex]

At the current time, the interior is 99% stripped, with just a bit of framing on the roof and side walls. But most, or all, of that is coming down this weekend too due to a saggy roof, and the repairs that I'll get to figure out as I go.

The current AC is a non ducted Colman model, probably the original unit from 1987, lol, and that's part of why I'm not sure if I want to reinstall or not - mainly just the loss of headroom in the center. I'm 5'10, and I just _barely_ squeezed under it with the original carpeting on the floor. If I insulate the floor, I'll be bending under the thing every time I pass it, and it's right in line with where I was planning on putting the stove/oven.

There's no room to push it farther up without sacrificing framing and insulation, nor is there room in the room to run ducting. Though frankly, I don't really see much of a benefit to running ducting in such a small space anyways.

I'm perfectly comfortable in temps up to 90* here in the desert with just some air flow, and I was thinking of just putting a fan in there anyways. I don't see myself camping out when it's 120 outside, so I'm leaning towards not needing AC...but then who knows what the future holds...

Oh, and the rebuild...while I would LOVE to just go buy a new one, or a slightly used one, I just don't have the cash flow for that, and I refuse to finance things other than the house. My belief was always "if I can't pay cash, I can't afford it", and that's where these old ones come in. Tons of labor and time to rebuild, but fits in the cash budget 🙂

[JBarca]

Measure the old hole in the ceiling will give you some info to compare to more modern day.

The current day standard for a travel trailer/Fifth wheels and some MH's, the RV AC unit is a nominal 14 x 14" square opening. They may be 14 1/8 to 14 1/4" actual.

Yes, rebuild with the structure and wiring in place. That same 14 x 14 nominal fits the standard 14 x 14 crank-up roof vent or powered fan, Maxx Air, Fantastic, etc., brands you can install in the hole if you do not have the AC now but want to add it in the future.

Your camper may have ducted AC in the ceiling of the camper, OR if all the air dumps out from the ceiling directly under the roof unit, it is a nonducted unit. If you have ducted AC, the newer AC unit control systems use both 12 VDC to run the controls and 120 VAC to run the fan and compressor. Some of the older ducted AC units created their control voltage from a transformer on the control PC board, and there was no 12 VDC in that area. Upgrading the AC unit later means you had to find 12 VDC and get it to that location. Both new Dometic and Coleman Mach "non-ducted" units use a simple older analog control that does not use 12 VDC. They use a capillary tube control to switch the compressor on and off. You turn the temp control knob like an older auto heater/AC knob.

Point: If your old AC did not use 12 VDC or have the 12-volt wiring near the opening, run a 15 amp, (14 awg wire) 12VDC + and - wire that will be live all the time and fused to the area while you have the roof apart. Just cap/seal off the wire ends to not short. You can use that same DC line to run a vent fan if you do not want to put the AC unit on now. You will only use some of the 15 amps, more like 3 to 5 amps, but you can tap into an existing circuit using little power that can be 15 amp fused already.

I hope this helps, and good luck with your rebuild. I have done many; it will take a lot of time, and if the roof leaks, the water can follow down the walls. The walls may be wet also from siding opening leaks where ever a screw went through or an opening in the side even if the roof did not leak.

These older camper restorations are a true labor of love.

John