I'm still trying to work all the gremlins out of the A/C on my 92 300SE.

The biggest problem I've been having lately is when I start the car after it has set out in the sun, the A/C comes on like gangbusters for just a few seconds (maybe 30 or so), then starts to slow down the fan speed way before the car is cool.

I previously had a problem where the fan would drop to low and not respond to the fan speed dial - a new regulator fixed that problem.

What I discovered yesterday involves 2 issues - one if which is a design flaw, the other is probably something wrong with the system itself.

The design flaw is the position of the cabin-temp aspirator sensor. I had inadvertently set the center duct positions where the airflow exits upwards at an angle. When the A/C comes on and the air out of the vents starts getting cool, the aspirator thinks the car is cooling down and backs the fan off. Leaving the vents where they were, I put my hand over the aspirator, and viola, fan ramps back up again. Solution was to make sure the air comes out more horizontally out of those vents.

The system flaw is that once the cabin starts to get near the right temp, the A/C bleeds air to the defroster ducts. On my car, the driver's side duct gets WAY too much air, which also rolls along the windshield and past the sensor, further confusing it. You can actually see condensation forming on the outside of the window by the defroster duct.

I'm guessing that there's something wrong with the short-stroke actuator for that duct. When the A/C's in full cool-down mode, there is no airflow from that duct at all.

Any suggestions?