The air conditioner on my 1998 ML320 works great when the compressor clutch engages. The engagement is becoming a rare event and now I will get a week of no A/c before it works again for one hour. When this problem started we took the truck into the dealer twice. The first time they replaced the fan wiring harness and upped fuse #44 to 40 amps. The second time they could not find anything and were very rude. We have replaced the AC Module (also called amplifier assembly 163-820-01-97) and I just changed out the pressure sender unit (163-542-04-18) and lost most of my 134A. I cannot get the refrigerant to charge back in because the compressor clutch will not engage.
Can you help identify the terminals I can jump to force the compressor to run so I can charge the system? Any thoughts on the root cause of the problem? The fans do run when the compressor is working and the belt seems fine.