I fully agree with your caution, persons must be very careful while the gauges are connected to the high side. If the high side is opened while adding refrigerant the can may explode!
I am familar with AC systems and have done all the AC work on my Rolls and my other cars for many years. This is the first time I have had problems with the Mercedes AC system.
I want to evacuate the system and see if the system holds vacuum then add the prescribed amount of refrigerant before extensive dye leak testing. The proplem may simply be a loss of 1 once per year.
I found a placard that the system uses 1.9 lb of refrigerant.
I can find the low side fitting but I still have not found the high side fitting in the engine compartment. Could it be under the car?
I am trying to get the pressures. Is the standard 2.2 X F ambient rule for the high side applicable to this car?
96 C280 Mercedes
82 Rolls Royce Silver Spur