I'll update this thread just in case someone comes across it later.  There were 2 issues: 1. The aftermarket pigtail had a diode crimped into the plug.  The compressor already has a diode built into the clutch. Another one isn't necessary and is a potential problem. 2. The REAL culprit....The damned...

The vehicle the compressor came from has a 2 wire plug. Inside the clutch is a diode ACROSS the coil windings. Wired properly, it shunts the reverse current from the magnetic field in the clutch when power is removed. If you ground the wrong wire from the clutch, the first time you energize it - yo...

Then you should have power to the clutch. Otherwise there is a wiring issue someplace. I DO have power to the clutch. From my original post... Not wanting to risk another compressor, I jumper the Low Pressure Switch and rig up a test harness that plugs in where the compressor normally would. I set ...

Tim wrote:You need refrigerant in the system to trip the LPCO switch. Should have power to one side prior.

LPCO is jumped to activate the circuit. No need for refrigerant just to test the circuit.

Revisiting my previous reply regarding the diode stripe. The diode body is solid black with a silver stripe on the positive end.

Tim wrote:Do you have refrigerant in the system?

Not at this time. It had one can in it each of the first two times we tried it.

Update to add info: Checked the wiring again. Appears to be correct with the following "question marks".... The harness plug is aftermarket and came with a diode in the back of the plug. From what I'm reading about diodes, this appears to be installed backward (black stripe should be on th...

I found this forum when a Google search lead me to this thread (Dodge truck in the thread but I'm having the a very similar issue) https://autoacforum.com/messageview.cfm?catid=2&threadid=19149 Vehicle specs: 1977 Chevy C30 dually. Gen 3 6.0/4l80e combo. Been running for a few months. Each head ...