In preparation for living in the desert some year and a half ago, I purchased a replacemnet for my primary (13.5K vintage 1992 ducted) ac with a 15K unit, and simultaneously purchased a second 13.5K unit to augment the cooling. I immediately installed the high capacity unit and stowed the normal unit in the front compartment of my fiver. That didn't work out, but I still had the AC unit stowed down there.
Now, many times people install the second air conditioner unit in the bedroom area, but in my RV for some reason the only heat problem is in the main living space - the bedroom remains cool and comfortable on airflow from the ducted unit on the hottest of days.
I recently started working from home and all it took was a couple days of 90 degree late-spring temperatures to convince me that it was high time to install my secondary AC unit.
I started by surveying the electrical possibilities. I have retrofitted my RV with a tankless water heater, whose power (for the blower/computer) is a rerouted wire that powered the resistive element in my old water heater - still even hooked to the switch on the wall in the kitchen with the pilot light. I decided this circuit would do nicely - resistive heaters use lots of current and so do air conditioners. And I'd only have to run the romex about 12 feet to connect, which was perfect, as I had about 14 feet of romex handy from the water heater project.
I started by removing the bezel of the center vent of the living area and drilling a 3/4 inch hole through the bulkhead there.That accomplished, I drilled a hole in the ceiling from the inside of the closet (above the tankless heater) Theoretically at least, that should be all the holes I would need.
Being unaware of how things might be routed above my ceiling panels, I pried off the beauty moldings and staples along the edges of the main cieling panel I had to transit. The outer edge of it was apparently assembled before the wall had been built. I used a utility razor to cut the panel at the wall. (I'll use the quarter round molding to hold it back up afterwards).
The back of the panel was glued to the joists, but it wasn't hard to pull it free. (one of the laminations of the thin plywood panel stayed attached to the joist) I now had view into the existing wiring - I could see the ducted thermostat wires, a number of 12V wires, and a line of romex.
I fed the end of the romex in from the vent bulkhead, and out the nearby light fixture hole. As you can see, these holes were installed in my rv with all the grace and precision of a ball-peen hammer.
I used that as a turning point to poke it diagonally up where I could grab the end of the romex from my revealed compartment, then routed it diagonally across the same to run down the hole I had drilled in the ceiling of the closet.
The romex was then just routed down the corner of the closet where I wired it expertly into my current electrical system. (if you're an electrician, you didn't see this) I'm sure I'll find a spare wire nut for that ground wire soon...
Shortly thereafter, I climbed up on top and removed all of the screws (like 30 of them!) holding the vent on top. I took some pictures of cleaning up the rubber surface up there from the putty stuff, but they didn't come out because I didn't pay attention to the settings on my DSLR.
I then had to wrassle the air conditioner onto the roof.
First I tried to just shove it up from the bed/standing on the rail. This did not work, I didn't have the leverage or strength.
I then had a theory that I could use a board as a rotation point, and hoist it up onto the roof by pulling on a rope, causing the board to angle up through 90 degrees with the board wedged in the side of the bed of my pickup truck parked close beside.
The theory was good, but I didn't have the required block and tackle to give me the pull strength. I estimate if I had a couple blocks I could have done it with a 3-4 magnification of my leverage. As it was, I just couldn't lift it - not even with an angle improvement thanks to the utilization of my sunfish mast as compression member.
I finally used the roof of my quad cab F350 - I pushed the air conditioner onto the bed, then onto the rail, then onto the roof, leaned it against the rv, then standing with my feet on the edge of the roof where the pillars are strong, heaved it partway up, then pushed it over the edge onto the roof.
That accomplished, I stripped off the packing material and set the AC in place on the hole. Inside I lined it up, attached the down-duct (a flexible foil/plastic skirt that routes the air from the AC unit to the distributor) and bolted the frame onto the cieling.
Wiring that into the power romex was trivial, three wire nuts, a collar and a screw later it was done. I fastened the bottom of the down-duct in place and did the smoke test. A snap of a circuit breaker and flip of the water heater switch and it wooshed to life!
The cool air issuing forth sure felt good on my sweat-soaked face.
I attached the distribution bezel and took a picture!
Here's the controls.
I sat down and took a well deserved break. Both air conditioners working together make the room fill with swirls of cold air. *AWESOME* Their compressors run at slightly different speeds, causing an interesting slowly-warbling vibration effect.
But there was still some work to do. The ceiling was dangling.
I dug up some brads and finishing nails and reattached it. I had to add some nails where the glue used to hold the panels to the cieling - I could have reglued it, but I don't have a brace to hold the panels in place while it dries and nails are easier.
My living space returned to more livable, I settled down to get some work done at my telecommute job, there on the hill, in Cameron, MO.
There is no doubt going to be some debate as to which unit I should set at a higher temp, and which to kick in as a backup. In the interests of quiet (I actually hate the blower noise of air conditioners) I prefer to run with only the 15K ducted, which doesn't run its blower when not actively cooling. So when I notice that the main AC is not keeping the temp down, I kick on the secondary with a slightly lower set point. It'll run continuously cooling the space. The sun will overwhelm it, though, and intermittently (1/10th of the time yesterday approx) the 15K cycles on and fills the room with cold, then it cycles off, leaving the 13.5K to contribute cool to the room while the 15K waits for it to be overwhelmed.
Once its clear that the evil heat from the sky is no longer roasting the RV, the secondary can be turned off and the main AC will cycle easily keeping things comfortable, and I can enjoy the relative quiet provided by the 15K unit not blowing when it is not cooling.
Viola. There you go. Don't be afraid to dismantle your ceiling if you need to, and remember - air conditioners and electricity are cheaper and/or more mobile than shade structures!
I wonder if I can modify the wiring on the backup AC to turn off the blower motor when its not above its temperature set point...
Yes, wired a NEMA 14-50R into the house myself. Although technically the breakers in the circuit are tapped off the unused electric dryer plug in the house, and only 30 amp to a leg, that is plenty to run both AC units since the two units are on opposing legs. A normal 50 amp port would have enough to run both on *one* leg. AND the microwave and start the refrigerator.