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  #16  
Old 12-28-2009, 02:18 AM
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Join Date: Aug 2008
Location: Pennsylvania
Posts: 65
Unfortunately, I never really got to the bottom of this. I just learned to live with the little problems. Now that its about 10 degrees outside, I won't be working on this again until spring. What I've taken notice to now that I've had this car for longer is that the clicking I speak of only occurs when the cabin temp control is set below max heat. If I jiggle around the temp wheel the clicking will stop. Also, I've accepted that heat will only come out of the defroster and floor vents and not the center vents (the air only gets slightly lukewarm coming out of those). I suspect the problem to be the unit of elaborate vent doors behind the climate controls. When I got a peek at it, some doors seemed jammed open while others jammed shut or even completely missing. I'm not completely clear on the problem, and I won't be until it gets warm enough outside for me to find out

Also, I can't get to the bottom of why the air coming out always seems musty and humid. The humidity from rainstorms seems to get buried into the system for days. For like a week after a rainstorm, I have to keep the AC on constantly with the heat just to keep my windows from foggin up. Any input on this issue?

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  #17  
Old 02-28-2010, 07:08 AM
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Join Date: Feb 2010
Location: Denver, CO
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Quote:
Originally Posted by tinypanzer View Post
Welcome to the forum, and to the wild and woolly world of W126 climate control......

Okay, first those vent switches on the center console..... The left and right sliders are supposed to control air flow to the vents on the far left and right. Sort of counter-intuitive. One would think it would control the center vents, but no.


Anyway, if you can't get air out of the center vents, it's probably the vacuum pod that controls that flap. The whole thing is controlled by engine vacuum, and it's a goofy setup. The electronics box sends signals not only to the blower, compressor, and monovalve, but also to a vacuum operated valve bank that uses electrical solenoids that control the vacuum signals to the flap pods......The electronics box decides which flaps open, and it's done depending on the settings. For example, heat will never come out of the center vents when functioning correctly. Only the sides, floor, and defroster.

Standard repairs to get it working would probably replacing the vacuum pods, and perhaps seeing if any of the manual flaps are damaged....... You will probably need to do your monovalve diaphragm at some point, as this controls the flow of engine coolant into the heater core and when bad causes heat in the summer and none in the winter.

The gasoline smell is worrisome, I would have your fuel system inspected soon. The blower intake is in a spot which tends to suck in engine smells such as oil and fuel leaks........
You say the heat will never come out of the center vents when funtioning correctly? I had the same problem as the person who started this thread, but I do have heat coming out of the sides, floor and defrost. I thought my heater was broken. It has been cold, so I have not tried the air conditioning yet. I know it works, but I just have not needed it. IF heat does not come out of the center vents what does?
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  #18  
Old 02-28-2010, 07:17 AM
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Join Date: Feb 2010
Location: Denver, CO
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Quote:
Originally Posted by 84MB500SEL View Post
Idk what exactly is wrong with the system, but I'll describe several problems with it that I experience- they may be related? First, with the three sliding switches directly under the front center vents: the one on the left seems to not do anything- whats it supposed to do? the one on the right also seems to not do anything- is it supposed to open a door in the air system, because it doesnt seem to affect the airflow in any of the vents- maybe both the left and right switches are broken? Only the switch in the center works- it controls air flow in the center vents- when its closed no air, but when open, fresh air always blows in, even in the winter when it's on recirc and I want only heat to blow in through the vent. The passenger side front air vent always has air coming out when the blower is on- no switch can stop the air flow. The driver side air vent never blows air out- no switch can turn that one on. Also, a smell of gasoline seems to be coming in somewhere through these vents- idk where from. I don't think there's anything wrong with the climate control electric module, but if this makes any difference, only when I turn the climate temp switches for the driver and passenger sides to below max heat, when I'm driving, sometimes it sounds like the blower motor or something around the glove compartment makes a buzzing noise, but it never does this when the temps are switched to max heat. Is there a fresh air door that's jammed or something? Is there a network of air flow tubes that has messed up doors (either stuck closed or open) or something? Does anyone have a diagram of the w126 cabin air system? Can you tell me any more info about this complex air flow system so that I can take it apart and fix the problem? Thanks.
THe gas smell means you need to tighten the bolts on your cylinder heads. I bought the new gaskets, but it was 20 degrees out side and decided I could put up with the smell. So I tightened the bolts about a month ago. The smell went away, and the gaskets are still in my trunk. Give that a try?
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  #19  
Old 02-28-2010, 07:33 PM
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Join Date: May 2005
Location: great state of va
Posts: 145
climate control

you may have a vac leak or the vac pump is weak
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  #20  
Old 02-28-2010, 07:55 PM
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Location: U.S.A
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wow,ive been following this thread,and my 89 300ce is doing the same thing,no airflow comes from the center vent,even when its fully open,there is a noise coming from behind the glove box,i thought it maybe the blower motor,but when the blower motor is off i still hear it,when i switch the blower motor to high everything sounds normal.imgoing to check the black box,its vacum controlled,im wondering if this may be whats leading to my surging up and down idle,from a vacum leak,should the vacum unit be replaced?is this what most likley causes the weird noise behind glove box?
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  #21  
Old 02-28-2010, 08:08 PM
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ive been following this thread and its been very helpfull,im having the same issues,the center vent will not blow even on high,there is a wierd noise coming from behind the glove box,thought it was blower motor,shut blower motor,still makes sound when cold in morning,when switched on high cannot hear noise,fan sounds great on high,auto and off position give off weird scratchy noise clicking sound,from behind dash.also the fan doesnt change positions when pressing climate control blower locations,air blows from all vents except for the double center vent.
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  #22  
Old 03-01-2010, 08:04 PM
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As far as I know, heat never comes out of the center vents when the system is working properly. Side vents, floor, and defroster vents only.
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  #23  
Old 01-22-2013, 09:03 AM
John Balwit
 
Join Date: Dec 2012
Location: McMinnville
Posts: 10
Does W126 heater/AC box in a '91 350 SDL interchange with 82 300SD?

Thanks. Also, pls point me in a better direction to ask this question if this is not the appropriate place.
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  #24  
Old 01-23-2013, 10:10 PM
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Join Date: Apr 2005
Location: Northern Louisiana
Posts: 481
The 126 heater boxes are prone to failure of the flaps which turn the heat on down at your feet; the hot air comes out of the defroster vents instead. It has one vacuum pod which opens a door on each side of the box simulatneously to warm the floor at the driver's and passenger's feet. The linkage to each door is plastic and the plastic parts break. It's a tough job to access (remove the instrument panel, etc.) so i am living with the situation.
The only other faults with my car are at least one vacuum pod is leaking again, and usually if I turn the clomate control on before the engine warms some, the switchover valve clicks repeatedly.
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  #25  
Old 01-30-2013, 09:44 PM
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Join Date: Jul 2005
Posts: 162
Also be warned that the plastic "pop-clip" that connects the vacuum pod on the driver's side of the heater case to the flap arm can break. At a certain point, if you really want things to work properly, a rebuild of the heater box makes a lot of sense. You can replace the disintegrated foam throughout, replace all of the vacuum pods, replace all plastic linkages, and get a replacement/re-soldered push-button unit, blower motor, etc. See my prior posts for details. If I were to buy a diesel W126 I would plan on doing this entire procedure before expecting reliable HVAC operation. You could also consider replacing parts like the heater core, expansion valve and evaporator. All of this stuff can and will break (heater core, expansion valve and evaporator not as much), so replacing parts piece-by-piece will probably just lead to lots of frustration.

Just be warned that you do not want to break the plastic "extension arms" for the footwell flaps when you take the unit apart. It is easy to do, and the driver's side flap lists for roughly $250 at the dealer.

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