I have a 94 c280 which has had an A/C issue for well over two years now. The system has been checked several times. A vacuum leak was suspected and some module that had vacuum hoses connected to it located in the engine compartment was changed because it had a hairline crack in it. It did not solve the problem. The symptom is still the same, start the car, start A/C, air blows nice from all vents and then air is directed to the windshield defrost after a few moments of running. Air is also cut from the lower blowers but air from the side vents is fine. I should also note, even though the air is directed to the defrost, it is always cold, the windshield frosts where the deforest vents are located.

On occasion, the air will blow back through the center vents for short period of time and then cut off again, redirecting to defrost. When selecting the various air distribution buttons, you can hear clicking like something is being switched but the air is not redirected. Air only comes in from the side vents and the defrost, nothing from the center of lower vents. If I hit the EC button on the controller, Air will be redirected to the center and lower vents but then warms up. Once I turn off the EC, the air stays on the center/lower vents for a short time then defaults to the defrost. This happens every time I hit the EX button.

I've been searching this and other sites for information on this issue and it seems that the issue is somewhat common and everyone points to a crack in a vacuum line or the two actuators next to the glove box, the rubber wearing out due to use. since it doesn't look like it's a bad vacuum line, I'd like to replace the actuators. Does anyone know the part number to those actuators and the procedure to replace them. Also, any special tools need for the job. Lastly, is it recommend to replace the vacuum line while doing this procedure as a precaution.

Any and all input to this issue and request is welcome and appreciated.