I just purchased A 1986 comanche with the Renault diesel engine, the truck has factory A/C. The system is empty. I went to hook up the gauge set and can not locate the high presure service port. The low side is on the line about 6 inches from the compressor. I have followed the high presure line from one end to the other including pulling the grill out to get a better look at the receiver dryer. The dryer does have a sight glass and limit switch. I do have the factory M.R.277 repair manual, nothing on port location in there. Thanks for any help.