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#11 (permalink) Old 11-11-2012, 01:15 AM
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If I understood correctly, he has 2 S420's on the lot and you got one that runs perfect but has a heater problem, while the other one has a water pump problem?

Keep the heater problem one, the duo valve is usually the culprit. You can take the part apart, test it with some 12 volt electricity wires and see if it opens up and closes. The part is cheaper than a water pump and is less work to replace, I did it myself and this is the first car I've ever worked on.

What you can do is check if the duo valve heats up on both cores (look at the duo valve and you will see it has two chambers, both should be hot.). If one of them isn't hot, then your duo valve has a problem. Ofcourse, the best way to test is it to take it out and check in my opinion. From there, you clean it up. If cleaning it works, great! If not, decide if you want to buy a new one or used one. I will warn you, I had 3 used duo valves fail on me within a month time. Only after those 3 messed up valves. I ended up finding my original one and taking all the duo valves apart and replacing the rubbers and working parts all into one to get a working one, since I was tired of spending all the money for new used ones. (Getting a new one right off the bat would've saved me the trouble).

If the duo valve works (via electricity inspection, it should make a clicking sound on both sides), then you might have a problem like the original poster did, with a messed up sensor.

Hope I helped, good luck!

Moved to new account "Perkunas"
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#12 (permalink) Old 11-11-2012, 08:29 AM
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Exclamation Center Air-Vents Buttons Issue

On my 1997 S-Class i have the following issue. The A/C works very well, and so does the heating, BUT when i press the buttons located between the front center vents ( red and Blue) the following happens :
1. When i press the blue button i get a nice strong stream of cold air from the center vents.
2. When i press the red button, the cold air stops and i only feel a weak stream of warm air, although i can hear the system making noise as if a strong stream would come out.
My question is if this is normal, or if something is wrong or stuck, and what can i do to fix this.
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#13 (permalink) Old 11-11-2012, 10:25 AM
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Originally Posted by Chono123 View Post
If I understood correctly, he has 2 S420's on the lot and you got one that runs perfect but has a heater problem, while the other one has a water pump problem?

Keep the heater problem one, the duo valve is usually the culprit. You can take the part apart, test it with some 12 volt electricity wires and see if it opens up and closes. The part is cheaper than a water pump and is less work to replace, I did it myself and this is the first car I've ever worked on.

What you can do is check if the duo valve heats up on both cores (look at the duo valve and you will see it has two chambers, both should be hot.). If one of them isn't hot, then your duo valve has a problem. Ofcourse, the best way to test is it to take it out and check in my opinion. From there, you clean it up. If cleaning it works, great! If not, decide if you want to buy a new one or used one. I will warn you, I had 3 used duo valves fail on me within a month time. Only after those 3 messed up valves. I ended up finding my original one and taking all the duo valves apart and replacing the rubbers and working parts all into one to get a working one, since I was tired of spending all the money for new used ones. (Getting a new one right off the bat would've saved me the trouble).

If the duo valve works (via electricity inspection, it should make a clicking sound on both sides), then you might have a problem like the original poster did, with a messed up sensor.

Hope I helped, good luck!
Both Sides heat up
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#14 (permalink) Old 11-11-2012, 07:54 PM
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Originally Posted by NewYorkS600 View Post
On my 1997 S-Class i have the following issue. The A/C works very well, and so does the heating, BUT when i press the buttons located between the front center vents ( red and Blue) the following happens :
1. When i press the blue button i get a nice strong stream of cold air from the center vents.
2. When i press the red button, the cold air stops and i only feel a weak stream of warm air, although i can hear the system making noise as if a strong stream would come out.
My question is if this is normal, or if something is wrong or stuck, and what can i do to fix this.
Anyone ?
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#15 (permalink) Old 11-11-2012, 11:26 PM
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At this point i dont know. This is chono123 by the way, made a new account.

The only thing i can think of now is the sensors/thermostats behind the climate control , there's 2 at 32 bucks each, but it doesnt seem to be the issue since cores are getting hot.

Did you consider the different valves that open behind the dash to redirect air as broken, not switching to hot air direction? Blower regulator maybe?

1997 S500 Coupe - Silver on Black
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#16 (permalink) Old 11-12-2012, 07:28 PM
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I have a 400SEL and the heat is very weak on full blast....however the windshield defroster gives me adequate heat.....where do you recommend I start to look for the culprit??
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#17 (permalink) Old 11-12-2012, 08:01 PM
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I have a 400SEL and the heat is very weak on full blast....however the windshield defroster gives me adequate heat.....where do you recommend I start to look for the culprit??
Duo valve isn't opening up fully. Clean it out if you're DIY. Mine had same issue, eventually heat will give out all together.

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#18 (permalink) Old 11-12-2012, 08:06 PM
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Originally Posted by Perkunas View Post
Duo valve isn't opening up fully. Clean it out if you're DIY. Mine had same issue, eventually heat will give out all together.
How do you clean the Duo Valve ? Will this solve the problem ?
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#19 (permalink) Old 11-12-2012, 08:11 PM
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Originally Posted by NewYorkS600 View Post
How do you clean the Duo Valve ? Will this solve the problem ?
Rear Air Conditioning System Repair, Duovalve Assembly | V12 Uber Alles

I cleaned mine up and it worked. Once you take the part out you can test it with 12 volt electricity. Hook one wire up to middle, and one to left or right. Both sides should make a little popping sound meaning it opened up.

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