Hi! I have a York Diamond 80 unit that was installed in 2001. I recently had a tech come out and charge the freon, but when we set the thermostat, the fan came on but not the compressor. (The contactor and capacitors were replaced last year, btw). The tech triggered the contactor out at the compressor and it kicked on, so he went up stairs and looked at the control board. He figured out that the ground wire in the wiring harness that connects to the circuit board (P031-01267-001) wasn't making contact, so he jammed it down into the clip, held down the switch, and the compressor fired right up. That was all well and good, but about a day later, the same thing happened, so I went in the attic, removed the blower unit door, pushed the wire, and it fixed it again. This happened daily for about a week, but the last time I reset the wire, nothing happened. I can hold down the contactor and the compressor starts up, but the simple ground wire trick isn't working anymore. The control board seems to be okay--when I press the switch, I get one red flash, then the blower motor kicks on, but no compressor. I assume the problem is with the ground wire, but now that I can't get it to work, I'm at a loss. Could the problem be with the control board? I know Johnson Controls have an upgrade available. Plus the harness is pretty hard to find for some reason. I would appreciate any tips you might have.

This is odd, don't see how pressing a wire inside has made the unit run, if the wire you were pressing was really the cause then the fan inside would not work either. By ground wire you mean the common on the control board?

Thanks for your reply! There's a pigtail that plugs into the control board--on the wiring diagram, the wire in question is referred to as "GRND" and it's green. The other end of the wire is screwed onto the blower housing. But like I said, I'm not sure this is the problem. The tech identified it using a voltage tester, fiddled with the pigtail (I think he said it was a "molinex" style connector), and then the compressor came on. He was a great guy--explained everything he was doing as he went along. I'd have him come back out, but I'm capable of replacing the circuit board and the wiring harness myself. I just don't want to spend $120 on those things if the problem is something else.

One other thing that might be helpful--he said the reason the ground wire was connected to the blower fan housing was because the control board was sitting on plastic (insulated) supports. And I don't think I answered you directly above--I don't know if it's the common for the system. I'll try to get a wiring diagram online.

Do you have a volt meter? Check for 24 volts from y to c at the control board when the t-stat is turned to ac.