terminal 12 (air compressor ) is not grounding so A/C wont turn on l need diagram to know what to look for in the PCM

go to a dealership and ask them they should have diagrams that go back to 99.

l will take a stab at ur question 4 cyl truck ECM terminal 12 pink to compressor relay & terminal 21 green red to the evap case thermo amp 6 Cyl truck three A/C wires terminal 9 Black with Yellow wire to control the idle air control terminal 12 pink wire turns on the a/C relay & green & red sees the thermo amp & throttle switch Engine control Module A/C compressor uses a thermo amp sensor inside the A/C case that is a common non compressor start item. Easily tested wit a new part the plug is just behind the glove box. Do not back probe with 12v [power] any of the ecm grounding circuits u could ruin that circuit. Also If the A/C relay is melted it may have taken out the ECM. Fix the relay & relay plate then replace the ECM. Good luck