I have a 98 E300 I have had for a couple of years and every since I have had it, it will cool great and blow ice cubes but at random will just stop cooling. AC compressor clutch is still engaged but it just stops producing cold air. It seems to do it most often when the set temp is reached or close to being reached and while driving at a steady speed. If you push the EC button to turn compressor off, then back on it will start blowing cold again. If you vary the engine RPM quite a bit such as during a downshift, it will start blowing cold again as well. I have also noticed when its hot outside such as around 90 or above, when accelerating hard, you can feel the car sort of jerk or surge, and can often hear a chirp which I figured out was actually the compressor clutch slipping, not the belt.



In the last couple of days I have started driving it with the sensor data showing. For the pressure reading, static pressure seems to be about 4 bar. When it is first cooling, it will get up to about 15 bar, as is starts cooling the car off the pressure seems to drop to about 7-8 bar but still cools (it was about 75 today). At seemingly random times the pressure will drop to 4-5 bars and blows ambient air. If you either downshift it, or press ec on and off pressure will jump back up and it starts cooling again.


Last year I replaced the expansion valve thinking maybe it was getting stuck, it made no difference. I discovered the aux fan was dead, so I replaced it and it now runs and I thought it fixed it, but it did not.


I am thinking that the valves in the compressor are sticking open or something and it stops building pressure until the compressor is either shut off then back on, or rpm changes and it knocks them loose. Does this make sense?


I also checked the error codes are there are none. Everything with the ACC seems to check out. I even tried swapping the control unit in the dash, still the same issue.