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Hello everyone! I thought somebody might know what might be wrong with my 1990 SEC. The heater stopped working. The blower works fine...When I put the Defroster on...I do get hot air. Is there a fuse? anybody that can help me with this? I would really appreciate it. Thanks.
 

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Sounds like a monovalve. It is an easy fix; just get the insert.
 

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It's an electrically operated water valve that opens to allow hot water into the heater core.

If you have hot air at the defroster, you may have a bad pod. Do all of the dash vents work? If you have a bad pod, that will cause all hot air to go out the def vents. You need to check that too to be sure.

The MV is just inboard of the battery behind the secondary F/W.
 

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This might be somewhat off topic.

The Climate Control in my 1983 380SEL seems to be working well except that the forced airstream from the rear compartment outlet seems to be much cooler than the forced airstream from the front outlets when using the heater.

When I purchased the car the lower left instrument panel kick panel was missing. I replaced it with one from another gen 1 car. It was difficult to align the under instrument panel Climate Control down duct to the corresponding duct on the kick panel. What to do? I used a looped wire to pull the ducts into alignment and then I slid the wire out before the final tightening of the kick panel mounting screws.

Perhaps the problem is that the ducts are no longer correctly aligned.

My question is, might there be another reason that the rear compartment outlet is blowing colder air than the front outlets when using the heater?
 

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TalkieTime,
The rear vent in the console is only a cold air duct. you can shut it off with the lever. Heat for the rear seat compartment is produced by the hot air vents under the front seats.
 

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My car did the samething. Get a mono valve rebuild kit, very easy to install, located near the battery. It fixed my heat. The entire valve was pretty pricey if I remember correcty. The rebuild kit was not.
 

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TalkieTime,
The rear vent in the console is only a cold air duct. you can shut it off with the lever. Heat for the rear seat compartment is produced by the hot air vents under the front seats.
Chadahar,

Thank you for that advice.

On my car the rear outlet knob and it's metal mounting stub atop the slider mechanism is broken off and missing so I'll remove the plastic directional assembly and manually adjust the slider to close off the cool air. Then, in the spring, I'll readjust the slider for cool air. Or, better yet, I'll just get another slider mechanism.

Another question, is that rear cool air duct just forced cabin air or is it air that's been processed by the Climate Control?
 

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Climate control air. There is a lever actuated duct on the 'front' of the core. It is operated by that lever which moves a cable which is attached to that duct.
 

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Outside fresh air. Same as comes through the center vents. Not heated at all.
 

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Indeed, outside unheated air only from rear centre vent.
Unless you have the twin temperature wheel climate control more common in Euros and then the centre vent can be heated or cooled air. Odd isnt it.

Also if you happen to have that version its a duovalve as opposed to a monovalve. Just for info.
The single wheel system seems a lot less reliable at the age our cars are at, because of those dry solder joints.
 

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So glad I found this thread! Been looking and looking for days about this all over the internet. I have an 87 560 SEC with no A/C because of a seized compressor and occasional heat. I know about the A/C, it's only money! If someone has or knows of a verified good used compressor let me know or let me know of a decent supplier for a rebuilt one. As we all know, used parts are getting harder and harder to find for these old SEC's. This is my third one. I also need a drivers door window regulator.

As for the interior ventilation I know that behind the dash are several vacuum actuators that run the air to the various vents. What's happening now is everything goes to the defrost vents. Literally every few months I will hear a hollow clunk behind the dash and suddenly the center and L & R dash vents work and they will continue to work until I shut it off then it's back to the defroster vents for another several weeks or months. I can consistently get heat but only after driving for 15-20 minutes and the temp wheel doesn't really do much. If I have it set anywhere in the red I get moderate heat which is fine here in LA but even if I turn it up full it won't get any hotter. I guess the vacuum leaks are preventing the valves from opening/closing fully so the whole system must be leaking air like a sieve.

Anybody have any good pics or video of someone taking the lower dash apart so I can see and access those valves? Then, is there anything in there that can be repaired or does it require buying all new parts? A good source and costs for those parts? If some of it is repairable then I would love to read about it. I've had a few quotes from some shops and it's about 2000 just for the A/C and another grand or so for the behind the dash stuff depending on what's needed which of course they don't know until they can get in there. I'm willing to open up the dash myself if I can just get a few clues how to do it. Thanks all,

Bob
 

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There should be a brilliant dash removal guide in the DIY stickies.
Its not as hard as you might think to get full access to all the vacuum pods.
 

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There should be a brilliant dash removal guide in the DIY stickies.
Its not as hard as you might think to get full access to all the vacuum pods.
True, You just need patience and willingness to start doing diy and you will be able to save a lot.
I did this job even before i tried my first oil change.
 

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There should be a brilliant dash removal guide in the DIY stickies.
Its not as hard as you might think to get full access to all the vacuum pods.
dash removal is not necessary...
rmsmith's Homepage

click the link about center vents...
I think the systems are similar enough from what i hear from others.
 

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Ears, that webpage is great it's exactly what I was looking for. Even if it's not exactly the same as my SEC I'm familiar enough with older Benz's (I'm on my fourth one) I should be able to figure it out. Thanks for posting the link.

Ian, I just took another look at the DIY section and I see I didn't look deep enough. There's a post from 2006 that has the MB manual PDF that shows exactly how to remove the dash I just copied it to my desktop. Again, not my car but it looks pretty close.

I'm like a lot of guys here, I'm not a mechanic but I can swing a wrench, I feel pretty confident I can dig into this and get my heat working. The A/C is another issue, I don't have a garage with the proper equipment for that, it's just having a good shop do it and that's probably a couple of grand depending on what it needs. I haven't had the R134 conversion done, my other tech 4 or 5 years ago put some kind of subsitute in it that worked for several years until my compressor blew up. I have no idea what would be used now. My guy decided to move back to France so I lost a very good MB connection.

Bob
 

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Hi Guys, I'm having a similar issue with my moms car. I was hoping to get some advice. Heater only works while defrost is on and only while the car is still. If the car is going over 5mph, even the defrost turns cold. What gives? 1991 300se. Would it also be the monovalve? I'm assuming its not a duo valve as the car doesn't have many of the options the upper end w126's have.

I'll post this in another thread but if anyone has a DIY for adding a heated drivers seat to a car that didn't come with the option, that would be great.

Thanks
 
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