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Old 03-20-2009, 02:46 PM
rustyguns rustyguns is offline
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Join Date: Dec 2008
Posts: 7
Originally Posted by Walrus View Post
After reading numerous threads on this and other groups concerning the Climate control systems on my 560SL, I decided to "attack" the issue. Armed with manual and hand-powered vacuum pump, I dove into the project. My main concern was why the center vents ALWAYS remained open. Secondary, why heat never made it to the floor. Thirdly, why the def vents stayed open regardless of setting. I should mention that, prior to this, I bought a reman control system from our good friend, Germanstar, to correct a problem with the buttons, so I was sure the "electronic" parts were "up to snuff".

Forget what you read in the manual about taking the vacuum line loose at the firewall and trying the I-IV tests so eloquently described as a failure in the main air flaps will give an erroneous reading. Instead, dive right in to the dash, remove the glovebox, and test the circuits there.

#1 remove the #1 circuit vacuum line from the switchover valve and attach the pump. Evacuate to 300 or so millibars... YEAH! The dreaded legroom pod is functioning (no loss of vacuum when evacuated and watched). Guess I don't have to worry about removing the heater box to repair (spoke too soon).

#2 remove the #2 circuit from the switchover valve and repeat above. Ok, looks like the short-throw def pod is fouled up. Now I know why the def vents stay open (partially) all the time. I can block off the valve and stop the needless vacuum leak anyway. I can live with that... But wait, doesn't the center flap pod share this line? Hmmm Why does it stay open all the time anyway. On to the next test.

#3 test #3 circuit as above... Great! The long throw is fully functional. At least the long-throw def valve is working. I think I read somewhere this pod is accessible thru the radio hole (and instrument panel, Strife and others). Maybe I'll have a look later.

#4 test as before... Crap. No vacuum. Wait, lets check each side independantly. OK! Passenger side works great... Rats, Driver's side no vacuum. No Problem, block off driver's side and good to go. At least I'll have 50% fresh air when called for/desired.

Crank her up and try... HEAT IN THE FLOOR! now move the dial to cool... Floor vents close! I guess vacuum leak was culprit with legroom flaps. Now about the center vents????

Here is where I get the title... I now know for a fact that hell exists (other than my christian belief)... Where would you send the guy(s) who designed this system??? Pulling the radio is a cinch, and exposes a decent view to why the center vents stay open... You guessed it. The heater box is broken around the rivets that hold the center pod. Well, that aint getting fixed anytime soon. Wait, what's this... the vacuum line runs straight to the center flap pod? What about the shared line to the short throw def valve (did I mention PO had pod work performed by a MB dealer some few years ago)? Some idiot bypassed the short-throw! Guess why... The diaphram must be shot because it will not hold a vacuum. Well, while in here, let's test the center pod anyway. Hmmmm... will not hold a vacuum. Like I said earlier. That's not getting fixed anytime soon.

All in all, I did learn a great bit, and did get the legroom flaps working. I can count the project somewhat of a success. Its easy enough to open and close center flaps with a wood dowel, since the pod is loose in there (and not rattling since the vacuum hose holds one side). The def vents will just continue to blow, I guess. I may make me a heavy black rubber mat to lay on the dash, covering those vents if I get industrious. I'm just proud to have heat in the floor for a change!

By the way... Whomever removed the def pod thru the radio must be a genius (sorry I forgot who reported that). I recall Strife performing the act thru the instrument panel access, but thru the radio would be an more impressive feat!

Maybe on day, when I have more money than sense, I'll remove the dash and heater box and repair correctly... Don't hold your breath!

i have exact same symptoms. is there an easy way just to pin down or hold the defrost vents closed so the center vents work?

i am in AZ we dont need heat. we just need a/c. A/c works on outside vents and out the defrost, but on really hot days we lose too much cooling in the dash vents and it gets sweaty in there!
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