A/C Compressor inop
 

Hi guys,
I've recently changed a bunch of parts on the benz to get the A/C going. I replaced all the hoses, orings, drier, condenser and aux fans. I evacuated the system and charged the system. The compressor was running fine as I was charging the system but stopped when I reached a clear sight glass. I checked the terminals going to the compressor and dont have any power. There are three terminals on the compressor so I don't know what the third one is for. There is some sensor on the back of the compressor and the wires go to the compressor terminal block. I thought maybe it's a temp sensor for the compressor. I checked the pressure switches on the drier. The red one brings the fans on. The other one is closed and I assume it's either a high pressure switch or it's used to cycle the compressor. I thought maybe someone could point me in the right direction. The car is a 1990 300D with the 2.5 L

Thanks

I did a bit of reading and found the "sensor" on the back of the compressor is a speed sensor. A Klima relay monitors the rotation of the compressor to the engine rpm in case of a lock up. From what I traced on the wiring schematic, two of the three compressor terminals are for the speed input. The third wire is hot for the compressor clutch. I'm thinking Klima relay may be where the problem lies????

strange that it worked fine while you were charging the system, but stopped when the glass went clear...

what refrigerant are you using, and why did you fill until the glass went clear?

I am using R12. You dont want to see bubbles in the sight glass