Okay, this is a strange one. I am thinking vacuum leak somewhere.


'90 300SE. A/C runs decent, having been retrofitted to 134A.


With the A/C on, the airflow will come out of the center vents for a little while (usually). Then, without me doing anything to the controls, it will route all the air through the defrost slots.

If I put the system on EC (economy, AC compressor off), the air will come out through the center again. If I switch it back to A/C, sometimes the air will continue to come through the center vents, sometimes it will switch immediately to defrost vents. Sometimes it will run on center vents for a good long while and then just spontaneously switch to defroster again.

One thing that seems to be a pattern is that it will often switch to defroster under acceleration. This is why me thinks this is a vacuum issue.


Question is: Where do I look? What innumerable assemblies have to be removed to get to it?



Thanks much!!


Jamie