w140 Heater Control Problem - PeachParts Mercedes-Benz Forum

MINMAX · #1 02-22-2003, 07:35 PM

When using the climate control, heat doesn't come out of vents by the foot area. There is no heat dirtribution to the rear vent in the center console. Is this a Monovalve problem? The controls have no effect on which vents air comes out.

Gilly · #2 02-22-2003, 08:45 PM

I've recently learned that the vents in the rear of the center console won't provide heated air (unless, I believe, you have the fancy version of the rear climate control, look in your owners manual to see what the regular and fancy versions look like).
On the footwell heat, if you are getting heat in other areas, such as the dash vents and defrost, I doubt it's a mono-valve. As a matter of fact, it has a duo-valve anyways, not the troublesome mono-valve like the 124's and 126's had.
One thing to fiddle with as an experiment is the double button between the 2 center dash vents, it has the red and blue LED. Make sure neither the red or blue is on, see if that helps. I'm guessing possibly one of them is lit, probably the blue one.

Gilly

MINMAX · #3 03-03-2003, 12:51 PM

Thank you for your reply! Sorry it's taken me so long to get back to you. The light in the center of the dash was out. Maybe I'm just looking for more than there is... the vents directly below the dash do blow a little hot air but this just seems to me to be inadequate. The passenger control has no lights at night can that bulb be changed? What about the radio, can the bulbs in that be changed also?

Gilly · #4 03-03-2003, 08:34 PM

Lets back step a bit and find out some basics.
What year and exact model 140 is it?
Are you saying that the vents in the bottom of the dash (the ones that warm the front passengers feet) don't blow hot enough air, but the air out the center vents (the ones that you can direct at your face or chest) blow hot air? And also the windshield defogger blows hot air?
Does the engine temp gauge get up to a normal range, say 80 to 90 degrees C?
In regards to "passenger control" i am a little confused about that. I would tend to believe you mean the control for the passengers vent dial, but those are all in the center vent assembly; the left dial is for the left (drivers) center vent control, the center dial is for the center vent control, and the right dial is for the passengers vent control. These dials are all illuminated by a single bulb, which transmits light to the dials with a clear piece of light transferring plastic (similar to how a fiber optic strand works). I believe this was how all 140 chassis vent control illumination worked.
In regard to the radio illumination, no, it is not serviceable in the field.

Gilly

myarmar · #5 03-03-2003, 10:01 PM

Quote:

Originally posted by gillybenztech

In regard to the radio illumination, no, it is not serviceable in the field.

Gilly

I did this replacement in my radio. To change the bulbs in the radio you'd need to unsolder old 6 or 7 bulbs from the PC board in the radio front panel and solder replacements back in. I used replacement bulbs from Newark Electronics p/n 50N8166 (12 V, 0.06 A)
http://www.newark.com/NewarkWebCommerce/newark/en_US/support/catalog/productDetail.jsp?id=50N8166
To do this you need to be familiar with un/soldering of PC boards and have proper equipment.

MINMAX · #6 03-04-2003, 07:27 AM

The car is an Early 1992 300SE
WDBGA32E5NA048762
I replaced the thermostat as soon as it started getting cold out. The engine indeed never came to mid range temperature. I was hoping that would solve the heat problem. I do miss my heated seats. The 560sel I just sold was really nice in the winter.

Even cranking the heat all the way up, the air coming out of the vents just below the dash & steering wheel, in the drivers leg well, doesn't flow out significantly. It's warm, but there isn't much of it. Is that the only vent for the foot area? Shouldn't there be some more venting closer to my feet? I do get heat out of the defrost vents and center of the dash that seems normal. It's just my feet never get warm in this car.

The control that regulates the passengers temperature does not light up at night. From what you say it means my controls have been screwed with. I'm familiar with the optic lighting from my Porsche 928. Are you certain that it isn't a seperate bulb?

Gilly · #7 03-04-2003, 08:28 AM

No, I understand now. It is a seperate bulb. I thought you meant the 3 dials that open and close the dash vents. On your 92, I can picture what you mean now, you have the 3 "boxes" of controls for the climate control. I know there is a replaceable bulb for that, I'd have to look it up to see how you access it, I can't remember right now, maybe myarmar has ir memorized. Believe it or not, we are seeing less and less of the 140's already at the dealership.
On the airflow to the feet area, it would be better if you could compare it to another car, but this isn't a common complaint that I can recall. Maybe there is an actuator that isn't working right, ot the vacuum control box is bad. If I get a chance I can look in the diagnosis book for the climate control and see if they list this as a complaint and what the remedies might be. Becuase the temperature itself is OK, I wouldn't think it'd be the duo-valve. If I remember correctly, there is a "tunnel" built into the knee bolster which runs over to the door, and this in turn warms the door pocket (believe it or not---check it out). If there were a problem with either the fitment of the knee bolster or the seal between the bolster and the door panel, maybe you'd be leaking heated air and causing this problem. Does the passenger side feet area warm up OK, any complaints on that side, or just the drivers side?

Gilly

amosfella · #8 12-02-2007, 11:33 PM

I have the same problem on my 95 S320. Except I get no air whatsoever to my footweels. I have been trying to figure it out, but I haven't been able to yet. I have pulled out the glove compartment box, and had a look at the vacuum distribution block. I haven't tested it yet, but I can hear the vacuum going through it. It makes a sound like an air valve being opened, then a sucking sound, then a kind of a click. I checked the codes, it was a relay that was supposedly wrong. So I pulled the relay, then I cleared the codes and ran it for 600 miles. No heat the the footwells, and no new codes. It's about -20-30C here. So, you can freeze your feet really quickly here in that weather even with the heat that is working on max and the vents pointed downwards.
Any ideas how to check, and how to remove the vaccum lines?? What else is there to check?? Where and how to get at it??

hodag · #9 12-03-2007, 10:37 AM

Is the blower putting out 100% when you have the fan speed on max? I have had a similar problem in that the heat and AC output has been gradually declining, which I eventually traced to a failing blower motor regulator. When the regulator goes bad (and it seems to be a common issue) the blower motor does not get the correct voltage and runs more slowly than intended.

Does your air flow blast out of the upper vents and defroster or is it just a light breeze? If your air flow is reduced, then maybe you are not getting heat to more remote parts of the cabin. The wiki has a very well written article on how to access and replace the offending part in a 1998 S500. I also have a 95 S320 and the process was virtually identical.

http://www.peachparts.com/Wikka/W140BlowerMotor

amosfella · #10 12-03-2007, 06:42 PM

The blower works just fine it seems. Big blast of air.

I was working on it today, and it seems after relooking and rethinking that the air distributor in the console is stuck in the default/defrost mode. There is no air comming from any other vents. It seems there is no vacuum comming to the vacuum control/distribution block behind the glovebox. Any ideas where to start looking for vacuum leaks in the climate control system??

hodag · #11 12-04-2007, 10:39 AM

Sorry, I don't know much about the vacuum system. I am sure somebody else can offer some insight.

obwielnls · #12 12-04-2007, 04:58 PM

If you have no vacuum coming to the vacuum distribution point then you need to track that line back to the engine compartment.. Should be the same color/stripe.. You will need a mighty-vac vacuum tester.. Shouldnt be too hard to track down with the mighty vac tool. You might even just start under the hood and look around.. Done any work under there that might have knocked a vacuum line loose?