hi there!

I'm new to the forum, but well experienced on this issue....not because I know how to fix it unfortunately, but because I have the same issue!!....so if you fix yours, chances are we can try to apply that solution to my car, which happens to be a c280 1998 as well....so let's get started....

the ports are located, one at the front of the engine, next to the condenser, but it is on the front side of the car...the other one is on the line that goes from the inside of the car to the compressor...I will send You an email with the picture if you let me know your address...