Add/replace rooftop air conditioning unit

Provience · Sep 26, 2023

I'm sure there is a better way to do this, but that clearly wouldn't be for me.

Old coleman mach roof top air conditioning unit has been dead for probably many years on my class C. Figured it'd be no big deal to swap it out, it's only 4 bolts :rasta:

Couldn't find the exact model number on coleman/mach website so went ahead and ordered a new upper unit from etrailer. Advent (get it? add...vent...) Air AC150 and wasted the ~$35 on the coleman mach wiring adapter. Foolishly thinking i'd be able to use my existing thermostat and lower unit :homer:

https://www.etrailer.com/RV-Air-Conditioners/Advent-Air/ACM150.html

the old mounting plate with the distribution cover removed

It's got just the 1 plug that goes to the top unit and 4 painfully long bolts with springs to maintain tension

Climbed up top to see what it needs up top

removing the plastic cover makes it easier to move around. Lugged it out of the way and got to check out the hole in the roof. Looks to be not quite the full 14.5" industry standard based on the amount of excess flashing. Oh well, close enough to not bother with

soap, water and a scrub brush helped clean up a bunch of the old gunk.

Lined up the new unit and got it generally close from above. It is much easier to fine tune the location once down below

and the etrailer adapter plug to go between the upper unit and the old control box. Fit, no problem there.

Biggest initial issue was the mounting locations. the Advent air unit mounted at the very corners, the old unit mount more along the middle :homer:

and the new unit had an offset outlet, which meant i wouldn't be able to use my lower base plate. I briefly considered folding up a new baseplate and adding in some ducting, but it would have been difficult to re-route it to match the old air duct which wanted the inlets along both outsides and the outlets down the middle. No problem, they make a base for this unit. The old wall mounted thermostat was too wide for the mounting location, so might as well replace that as well. This will surely keep the job quick and easy :homer:

Nope. New base plate came in, fit up quick and easy. New thermostat was a digital unit and only used 4 wires, previous analog used 6 wires. New unit has 12vdc+, "comm" 12dvc-, "A", "B"....Old unit had 12VDC+, Furnace, High Fan, Lo Fan, Cooler, 12VDC-....New unit ran wiring up to the roof unit and then from there down to the furnace, this also means I am not going to be running the furnace without having 120vac power. Kind of lame, oh well.

After a good bit of pondering, decided to just run some new wires along the inside rather than do the "clean" way of removing a bunch of cabinets and floors to run wires under the floor and walls and roof.

At the furnace I've got 12vdc+ [red furnace, blue coach] 12vdc- [yellow furnace, white coach] 12vdc+ to thermocouple [blue furnace, red to thermostat] 12vdc- to thermocouple [blue furnace, white to thermostat]. The red wire from thermostat to blue wire to thermocouple just goes down to a scotch lock tying it into the red furnace 12vdc+ line.

This will work as the new air unit control on the lower unit has a red 12vdc+, black 12vdc- and a brown "furnace" line.

and a picture of the coach wiring bundles and the main ground bus bar

M92PV4U · Sep 26, 2023

I was really hoping that this was going on your ford. :laughing:

Provience · Sep 26, 2023

Out of a great deal of annoyance I went ahead and doubled up some 18 gauge wire because it is almost the same area as a 14 gauge wire, rather than just buying more wire.

and had to add some length as well

Satisfied that i'd be able to find all the wires a home, went through and got everything tucked up. 120VAC stuff gets it's own little box. A coach is like a house, so wire nuts are life :rasta:

and played around with where I wanted the wires to go so that I could get them mostly out of the way. you can really see how much smaller the newer air register is compare to the old one, still need to get some good carpet cleaner on the roof there.

some self adhesive wire covers from the hardware store, probably going to have to set a couple screws in there to keep them up. Used just under 5' in length total.

and made a few ugly solder connections down at the junction location. tossed some heat shrink around the thing at the end to help keep the wires together

Provience · Sep 26, 2023

and tucked out of the way

fit well enough that I didn't need to trim the seat base.

and the new thermostat in place. Now it has a 3 speed fan. it was 97* inside so i'm not able to force on the furnace to see if it is working and I didn't install the extra start capacitor for the A/C unit, it would only short cycle before cutting off. Not getting any errors and the generator is about out of fuel and audibly struggling, so i'd imagine that low power is to blame at the moment. Those are both tomorrows problem.