My '84 190D is really starting to get me down! A few months back the HVAC began to act up. I was getting heat out of the side vents while operating the AC. Then when it got a little colder I couldn't get any heat to the floor. During this time the engine began shutting down slower, in other words it took a few seconds before the engine would shut down after the switch was turned off.

Well, I figured I had a ruptured HVAC Vacuum Pod somewhere in the system so I removed the dash (after testing each line at the vacuum distributor located behind the glovebox) and removed the double element pod behind the instrument cluster and the double element pod behind the radio because both showed signs of diaphram failure after testing. I ordered new replacement diaphrams from Autolux ($6/diaphram) and repaired them.

I put everything back together and began to test it out and found that I have no vacuum going to the pod behind the instrument cluster. All lines are intact under the dash. The water pod at the firewall under the hood works intermittently. The center vents work all the time unless I close them with the manual lever at the vents themselves. When the water valve works everything works fine with the exception of the pod behind the instrument cluster. That pod works when you apply vacuum via a MityVac hand pump but that's it!

Here's the thing about the water valve... When it doesn't work you can "tap" on the temperature wheel side of the CCU and can hear the vacuum distributor click and voila, you have heat.

The engine shut off works GREAT when you plug off the HVAC line that shares the same feed line with the sutoff.

I am wondering if I have a bad CCU as well as a bad vacuum distirbutor. I have checked all the lines in the engine compartment and cannot find anything that is questionable.

I am about to throw in the towel on this one unless you guys have anything to help me with. Believe you me I have searched!

Kevin

I don't know if its relevant but the 82-85 123 ACC systems use 5 vacuum control solenoids to distribute vacuum and operate the system. 3 of the 5 in my car leaked badly. Changing them made a huge difference in ACC operation. Maybe your car has similar solenoids? RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K