My bother's 2003 E320 Air Conditioning stopped working. When I put the gauges on it. Low side goes from 95lbs to 75lbs (after starting the engine). The High side doesn't barely budge and stays around 100lbs. When I rev the engine, the low side barely moves 5lbs to almost 70lbs.

I tried to add some Freon, and it made no difference at all. While all of this is happening, neither of the lines get hot or cold, and the pressures stay consistent (no cycling).