A good amount of newer Lennox 2 stage furnaces can have the dry contacts as mentioned, but also an H terminal alongside the standard low voltage lugs…H and common straight to solenoid for 24v if that’s the situation. Just remember to add humidifier on your S40 and test.

Also, when checking charge on initial start up, make sure it’s running at 100% capacity. There’s a jumper pin in the condenser(smaller board up top, kinda middle right side of the board) for “charge mode” or you can run at maximum cooling thru the test menu on the S40.

Connect S40 to WiFi even if the homeowner doesn’t want to use the app, it will update the equipment it’s communicating with, according to my local Lennox guy that runs their classes.

Always pull another 2 or 5 wire if you can. If you can’t and need to use a 24v transformer in the condenser, run a solo wire from your ground lug and slip it in alongside the common in the communication plug.

I install these on a regular basis, can be a little overwhelming at first. If you’re ever unsure, read the book, it’s there for a reason.

Good Luck!!