1995 Suburban HVAC Control Head Inoperative

1995 Suburban HVAC Control Head is inoperative. Air only from floor vents, irregardless of knob. A/C light and clutch do not engage when button pushed.
Recirc light does not light when button pushed. Fan speed works. Rear defog works. Fuses are all fine.
Found the following post by someone with similiar problems.
Unfortunately the control board is not labeled with designations. There are 4 transistors on board labeled 4692, 4687, and 2857. Looks like the 2857 one has overheated a bit. Does anyone have info on what can be replaced on board to repair this?
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