I hope you don't mind me tagging on here. I am a newbie to MB, having bought my first 300d (1985 - 85k) just 3 weeks ago. I just returned from a 2700 mile trip and noticed that my climate control system is not quite right. As it's been cool, it was not apparent at first. I had the system checked while on the trip. It was indeed upgraded to the R-134a, but it had an odd looking threaded low side shrader valve. This was replaced with a standard valve, and the system was charged with R-134, oil, and dye.

1. The AC does not cool at highway speeds (2900-3300 rpm). It works OK (meaning I wish it were cooler, but it's still better than highway speeds) just driving around town.

2. If I select ECON with a cold temp selected, it blows warm (not totally hot) out of the top vents. Selecting back to AC will cool it a little, but it's still warm....even with MIN selected on temp wheel.

3. Last night night I had it in cool outside temps. I selected ECON, and set the temp wheel to MIN. Air came out of the proper vents (upper), but it was warmer than OAT. If I set the temp wheel to MAX, the air would flow out of the foot vents, but at the same temp as the upper vents, i.e. no hot air, just mildly warm.

4. AUTO fan appears to work OK.

This seems to be an issue with the heater core valve. Am I on the right track, and is this something that I can take care of myself? Do they tend to stick? I am assuming it's vacuum controlled like almost everything else.

Thanks in advance,

Jon