This is a long story. The short version is, the outside AC unit won't come on, and needs to be re-wired.

Here's the long version: My house sat empty for a couple years before we moved in. I think while it was empty, the dude cutting the grass weed-whacked the control wire going to the AC. I tried running a new wire into the attic where all the wires going to and from the AC, furnace and thermo meet, but it's wire spaghetti up there and I don't think I did it right, because it never came on. Last spring I had a friend of a friend look at it. He said it needed re-wired, but he never came back, got busy with work, etc. Later last summer I called a repair guy, and he said it needed re-wired, and would have to come back. We couldn't afford it at the time, so he never came back. We still can't afford it, so I want to re-wire it myself. I've been around the forums a bit, so I'm not a total idiot, and I do video professionally, so I'm not a total stranger to wiring.

I have the manuals for my furnace (Goodman GPD125-4) and thermo (White Rodgers 1F80-51) but not the AC yet (York KA55HX45Y). Looking at the wiring diagrams, the yellow wire from the thermo goes to the "Optional Condensing Unit" and a wire from the OCU to ground on the furnace chassis. Is the Optional Condensing Unit the AC? If so, then I need to run a wire from the thermo to the AC then to the furnace, correct?

I attached the wiring diagram for reference.