I just serviced my 1998 ML 320. Not sure if your setup is the same.
You will see 2 silver pipes, one larger (LP) and the other smaller (HP) coming out of the firewall to the right of the battery when facing the vehicle.
The LP (Low Pressure) port is located next to the battery against the firewall.
The HP port is located in the front grill area, at the right, between the headlight and the rad.
Although, the LP dust cap is supposed to be Blue and the HP cap Red, mine are both Black.
Always add refrigerant through the LP port while the compressor is running.
Always use an approved refrigerant. R12 and R 134a are no longer legal for use.
I used a REDTEK kit and products. Go to: www. REDTEK. Com for more information.
Thursday, June 11th, 2009 AT 10:55 AM