When I installed an air conditioner in lil' yeti this summer, the short goal was to get it working. The window AC unit had the typical built in thermostat. But those knobs with their number scales are not obvious to tune. Nor well calibrated.
No worries though. My longer goal was a proper wall thermostat. With digital precision and large numbers that're easy to read. Just set the desired temperature and forgetaboutit. I just wasn't impressed with local store offerings. I specifically wanted a simple, non programmable model. Thank goodness for online shopping.
Like most residential thermostats it operates on low voltage signals. To make it work for my application required an interface module to cycle on/off power to the compressor. Plus the AC unit's fan, which has two speeds: low and high. Like most thermostats mine didn't support two-speed fans. So that became another requirement.
My solution was a switch on the interface module to choose the fan speed. The interface is buried in otherwise dead space under the front cabinet. So the switch is hidden. But that's fine. I figured the fan speed decision is not likely to change often. Perhaps seasonally. Possibly after moves to different climates.
Practically speaking, with maybe 50 square feet of interior space a 5,000-btu AC should keep up on low. And make a bit less noise. Still, it seemed prudent to enable the high output option. Just in case. Call it Murphy Insurance.
Rewiring a window AC unit for remote control isn't as difficult as some might think. Ya start with the schematic for how it's wired internally using its built-in thermostat. Just open it up and look for the sticker.
Once ya know what to look for, it's just a matter of connecting the dots. Since RVs already have a convenient 12-volt source, why not just use automotive relays? I found some nice ones online at reasonable cost. I thought the built-in blade fuse holder was a nice feature. So 12Vdc relays were what my interface module was designed around.
The air conditioner could work with only one relay. The fan could be hard wired parallel to always turn on/off with the compressor. But like most thermostats mine had a fan switch. Auto cycles the fan with the compressor. Manual leaves the fan on without cooling. That could be handy. And since the thermostat had the feature, why not use it? That just required a second relay. No biggie.
I wanted lil' yeti to also have central heat. After considering a number of options I chose a baseboard heater. Why not have the wall thermostat control the heater too? That just added a third relay to the interface. Here's my design.
To build the interface I decided to use a piece of 1/2" Delrin that was available. I hid the rat's nest of wires on the back side: out of harm's way. The front was reserved for terminal connections. Plus access to the fan speed switch. Up = high. Down = low. Intuitive enough.
This thermostat mod took an embarrassing number of weeks to complete. Partly because I misplaced the t-stat wire I picked up for the project early this summer. In my defensive I got distracted with road and field testing of lil' yeti while juggling other priorities. Alas, here in northwest CO with fall temps now dipping below freezing overnight this mod finally got prioritized.
Of course, just after buying replacement t-stat wire the original stash turned up. Thanks, Murphy. To my pleasant surprise, the local Ave Hardware let me return it. No problem. They didn't have to. It was cut from a spool. Wouldn't that be harder to resell? I half expected a no-return policy on cut wire.
Full disclosure: this was a test. It was only ten bux. Not gonna break me if they didn't let me return the wire. And I'd use it for something. Eventually. I just didn't need the inventory until someday. After six years on the road the packrat urge continues to be a dilemma. Not a bad problem for a traveling project junky. Just rambling.
Back to that wire remnant I returned to Ace. Although it was cut from a big spool, it wasn't cut for me. That's exactly how I found it on their shelf.
Ya see I measured ten feet needed. So I decided to buy twelve. Then in the store I saw fourteen and figured close enough. The Universe maybe knew how I tend to under estimate. (Like a two-week cabinetry job that took two months! Ahem.)
I was kinda looking forward to a discussion if they balked at returning cut wire. Just to see how they handled the fact that it wasn't me who had them cut it. But nope. "You wanna return it? Got the receipt? No problem." Nice.
Maybe I could've saved a few bux buying a baseboard heater online. But Ace had a good product at reasonable price in stock. I was more than happy to give them my business. Thanks, helpful hardware folks.
Lil' yeti now has a proper heating and cooling system. The wall thermostat works just like you'd expect. Who says living in a tiny camper means roughing it? Without any creature comforts or luxuries of home? Who indeed.
