So I thought i had an intermittent problem with the relay board on a York RTU. Ordered a board and went back yesterday. The unit was operating when I got there. figured I would change the board and save the original as an emergency spare. After swapping the boards guess what. No damn cooling. I had to put the old board back in. It was the end of the day and they were going home. I'll attach a copy of the wiring diagram. Could someone shed some light on the sequence of operations of this unit.