Been super busy installing the swamp cooler, as the weather is getting downright warm at times. I finally got the duct, but haven't installed it yet because the electrical conduit needs to run behind the duct. Installing the duct first would have made the electrical a nightmare (and it's already pretty nasty).
There are two ways to control a swamp cooler; one is line voltage. Line voltage is when you run big full power (120V) wires to a switch on the wall, then run a bunch more big wires to the swamp cooler. That's a lot of expensive wire (copper ain't cheap!) and those switches tend to burn up in a few years when run that way.
I chose the alternate way, which is low voltage. If you have a furnace or central A/C with a thermostat, that's exactly how those are all controlled. Your furnace or A/C has a little transformer in it, that produces a small amount of safe, low (24V) voltage which goes through inexpensive little wires to your thermostat. You'd get a tickle from it, but it shouldn't kill you or start any fires.
Ordinarily, you'd need to purchase a swamp cooler specifically designed for low voltage ($$$), or purchase a $150 conversion kit which is an ugly box mounted to the outside of the cooler. I didn't like those options, so I used something called a RIB from a company called Functional Devices. A RIB is a "Relay In a Box", and a relay lets you use low voltage to control line voltage. Neat, eh? The other nice thing about these RIBs is they're individually replacable, so if one fails I'm just replacing one $20 RIB and not a $150 control board.
So, I tapped into the low voltage source from our gas furnace:
You're not required to do low voltage connections inside a box like you are for line voltage, but I put mine in a box anyway just because I wanted things to be tidy. I'm saving a ton of money by doing this myself vs hiring someone, so a couple more bucks isn't going to break the budget.
The inspector actually didn't like how short I left the above wires, so if you do something like this be sure to leave 6" free length on each conductor. But, the inspector let me slide this time.
Rather than have these RIBs mounted inside the swamp cooler (subject to moisture damage!), I mounted them in the attic on a scrap of 2x6 lumber. Mounting everything to the lumber beforehand let me do most of the work in my cool, clean, well-lit workshop standing comfortably rather than laying facedown in nasty insulation at 100°F:
The blue box off to the right side houses all of the low-voltage connections, so that only line voltage connections exist in the main gray box. (Don't want to mix the two together, for safety reasons.)
The inspector passed my work (and by the way I also got a plumbing permit for the water line and that passed inspection as well) so now I can try to figure out how to install the duct... hopefully before we start getting too many 80°F days!