CCU unit only blows thru Defrost vent
 

Suddenly... now that the weather is getting hot, my climate control unit decides it will only blow HOT air and only thru the defrost vent at the window. Regardless of setting! I also notice if I rotate the temp control I don't hear the usually "clicky click" that signals to me the unit adjusting output based on ambient temp.

I stumbled across the thread below, but not sure that it applies to a 300D like my '82.

http://www.peachparts.com/shopforum/diesel-discussion/250896-my-heater-only-blows-though-defrost-vent-300sd-82-a.html?highlight=defrost

Thanks for any wisdom on this...

-Chuck

sounds like you may have a problem with the pod switching system, they tend to break after awhile and the system will revert to the Defroster setting when the vacuum pressure escapes. that is my guess, that is what happened with mine.

Answer.
 

The default/neutral blend door position is defrost = vacuum failure.

Possible cause:
* Vacuum hose leak.
* Vacuum element Diaphragm ripped.
* Vacuum pump failing.

Full heat is a common issue:
* Mono valve Diaphragm ripped.
* No voltage to the mono valve.

Aux. Water Pump takes out CCU
http://www.peachparts.com/shopforum/diesel-discussion/140870-aux-water-pump-takes-out-ccu.html

Climate Control Repair
on the 1983 300D Turbo (W123 Chassis)
by BoostnBenz
2/16/04
http://www.peachparts.com/Wikka/W123ClimateControl

The CCU can go bad and there are threads about re-soldering them, if that is the problem. It could also be the pods which are not opening and closing according to the signal sent out by the CCU if it is working properly. But to eliminate one variable, do you know that you have a good charge in your A/C system? Was it blowing cold air recently? This season? Have you put a gauge on it to see where the reading is?

Are you running R134a or R12? The R134a you can charge yourself with supplies from the auto parts store. R12, not as obtainable.

I find that I have to recharge the system each summer, but it holds the charge for the hot months.

If this is any hint on the CCU -- for the last week or so it was only working on "full blast" mode -- the lower speed would start up low and within a minute go to the full output. Typically I just use the vent-air blower, not pushing the compressor button. I'm in New England so not hot outside for much of the year.

I'm thinking vacuum issue rather then CCU, though that's only because WANT it to be that -- I replaced the CCU about 18 months ago, but with a junk yard replacement that has worked OK.

Thanks for the bullet list WHunter -- will go through this. Also I have been mucking around with another electrical issue, I'll want to double check fuses I saw some corrosion around contacts and such. Would be wonderful if this boiled down to a poorly-seated fuse, but maybe that's not in the cards.

-Chuck

only one way to tell if it's the CCU really is to switch it with a known working one, So I've been told..

Update
 

By way of update: my hint today was "the horn isn't working." It was the #14 fuse. Fuse was actually intact. Seems like we have aluminum fuses with copper contacts, is that possible? What a recipe for reaction/corrosion. In any event, in the mean time I learned quite a bit about location of vacuum pods from the link below, but am quite glad that it was simple (dumb simple) to solve.

Great write-up on HVAC pod locations and overhaul approach:
http://www.peachparts.com/Wikka/W123HVACVacuumActuators

Thanks for all the great info from the wonderful folks on this board, I'm very grateful, and I'm much better prepared for the actuator overhaul that I will likely need at some point!

Chuck

Good Job finding it though. Many times the simple fix is the hardest to find.

When I picked up my car it had the same problem. I pulled the CCU to check for bad solder joints but instead fount that there was a small fuse in the back of the CCU and it was blown. Replaced the fuse and everything started working.