I don't have the diagram, we don't actually need it. Let me know if you want to proceed from there or not.
If you do, turn the power to the unit off, triple check it with a known good meter. mark all 3 wires connected to the compressor body itself, very carefully, make a sketch of which wire goes to the C, R and S terminals. Look for any burnt or over heated terminals.
Then se your multi meter to measure OHMs across each combination of those 3 pins on the compressor , for instance between C and R, C and S, and S and R. the reads will all be under 10 ohms. Then check each terminal to the copper tube tubing on the compressor.
Next set your multimeter to 'micro farads' (uf)... and test the compressor run capacitor. after shorting the terminals across with an insulated handle screw driver.
Make a careful diagram of how the wires connect.
Measure the micro farad reading between C and R, or Com and Herm... tell me what read you get... it should be in the 20 to 40 micro farad range.
We can go from there.