I currently have a Nest controlling my LP furnace. I'm getting an evaporative cooler installed and I'd like to also control it with my Nest. This post gave me a good starting point, but I'd like to expand on it some to
- Be able to control 1 stage heating, 2 stage cooling
- Keep manual fan control of both furnace and evap. cooler
- Automate pre-wet stage (pump runs for specified time before fan kicks on)
Since I'll have a dual transformer system, I know I'll need to use both the Rh and Rc terminals, and run the C from the cooling side. Here's is my first WAG at a schematic (sorry if it's confusing, first time drawing a schematic).
Please let me know if I've made any boneheaded mistakes, or if you see any way I could improve it. The only thing I'm missing is fan only in high speed, but I'm not sure if I actually want that (I rarely run the fans, I more just like things installed to work properly/as intended), and pump only (but the only point of that setting is to pre-wet, which I'll accomplish with the delay).
I'm willing to lose manual fan control if you guys think I should just drop that (remove heat fan relay and cool fan relay).
I don't think my heat fan relay works as wired (if I called for just a fan on my furnace, the W wire wouldn't energize, otherwise I'd be getting heat too). Also, I think the G terminal on the Nest is only powered by Rc, so I'm not sure I could get manual fan control of my furnace (maybe with a latch relay as @JPhi1618 suggests, but that would require user logic that I'd rather avoid). So I'm dropping fan control.
I also wanted to make sure the fan was delayed if the Nest started in high speed, so I moved the location of the delay.
Finally, I was having trouble finding appropriate DPST relays, so I changed the cooling relay to a SPST.
If I don't hear any objections/comments, I'll order some parts, breadboard it up, and check back in with this post to update how it goes.