I installed replacement diaphragms in 4 of the 6 ACC vacuum actuators in my 87 300SDL today. Pretty easy... for the recirculation (2), defrost and center vent actuators. I'll wait for the footwell and diverter actuators to fail before I touch those.

I replaced the center vent actuator diaphragm without removing the actuator. The other actuators were difficult to open so I thought I'd have a difficult time with the center vent actuator since there's a lot of hose, wire and bracketry in the way but the top part popped right off.

I used one of the diaphragms without a hole in the center vent actuator because that actuator has a rivet type lever and I couldn't reach the far end of the lever to release it with the actuator in place. I jammed a replacement diaphragm in the cup -- it's a tighter fit than the other cup locations and I had to spin/threadthe spring into place. It took three tries to get the diaphragm to seal properly against the cover but it finally did.

I would have taken pictures but there are no good angles from the bottom of the dash to show how to remove and install the actuators.

The diaphragms come with instructions so there's no point repeating those steps here either.

If anyone has questions, please ask. If anyone has a better way to do this, please contribute.

Oh, with the ACC control panel out of the way, I replaced the dead bulb in the middle of the fiber optic distribution 'spider.'

Sixto
91 300SE
87 300SDL
83 300SD