Location of low side port, ML 320 A/C?
 

I want to charge my 99 ML320 with 134A Cans that say they attach to the low side port.
The only low side port I can find is on the pipe just in front of the passenger side of the car.
The connectors from the cans will not fit on this low side port ..... Do I need an adapter, or is there some other port that my commercial 134A containers will fit. I can't find any!!!!

I called the mfg of the 134A products and they said Mercedes may have a port which only Mercedes shops can utilize. This whole thing is very strange and I need to find some answer or I will have to pay $150 to a shop just to get a recharge.

Will someone please explain this to me? Thanks, Ben Carter