I am having problems with the blower motor on my S420, stays at low position even when it is at high speed. The air is very cold, but seems restricted. I have read a lot of posts on different boards. I was getting ready to order a blower regulator when I stumbled upon a reply about cabin filters. Now I want to check that first, as I have in my younger days spent a lot of money thinking I was smarter than the mechanics, bought parts only to find out it wasn't the problem. Ended up taking it to a mechanic to fix in the end. Had the parts left over for later. Now how do I find the cabin filters as it seems impossible to find a good mercedes repair manual for late models.

assUMING That the car is a W140 chassis, the blower motor & cabin filter is under the hood! Simply remove the air intake at the rear of the engine area & then you will find the micro-dust filter & under that is the blower moror with electronic regulator!

THE MBUSA factory DVD(W140 chassis) covers that info. Either call 1-800-for-mercedes or go to local dealer!

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MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Bower motor shaft rusty, mine finally quit turning. Took cover off gave fan a litle nudge and it started. Put oil on the bearing been working for weeks. The regulator sits on top of the motor they go bad $150 if the whole blower goes bad $650 with a new regulator

Thanks all, I will check it out.

Wasn't the cabin filter. The blower motor was turning. Think I have a bad regulator?

there is also the cabin air dust filter which is housed in a panel below the glove box within the front passenger's foot well. i recently replaced the one in my S420 and there was a very noticable increase in air volume - even more so if you take the old dirty crusty filter out and don't put the new one in right away - even more air blows sans filter!

...something for you to look in to as it's 'only' a $20 filter and it probably needs to be replaced if it never has been.

mike b.

there is also the cabin air dust filter which is housed in a panel below the glove box within the front passenger's foot well. i recently replaced the one in my S420 and there was a very noticable increase in air volume - even more so if you take the old dirty crusty filter out and don't put the new one in right away - even more air!

...something for you to look in to as it's 'only' a $20 filter and it probably needs to be replaced if it never has been.

mike b.

I am having the same problem with my 97' S320 air flow. I checked my underhood cabin air filter last night. I took it out and ran the system and only got a little better air flow than with the filter in place. On the interior air filter you described in your post, is it readily accessible or do you have to remove the cover of the passenger footwell?

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KCScout
98 S420 My Wife's Baby
97 S320 My road car
83 300D My old road car (love that diesel)
81 300SD Wife's former Baby
81 240D A fun stick shifter
71 220D My first one

it's very easily accessible. the panel is not actually on the floor in the footwell but on the underside of the dash/glove box. stick your head in the footwell and look up. there's one black panel with two circular vents and then another further back (towards the engine compartment) - that's the one you want. there are two slots where you can insert a flathead screwdriver and release the catches. the panel can then be slid out towards the seat. you'll find the filter housed in a little compartment in the panel. my old filter was black, completely clogged and twice as thick as the new (white) one.

let me know if this isn't clear enough - i think i have a diagram somewhere i can dig out.

I found a regulator in a salvage yard for my 1997 E300D for $75. They are in demand and tough to find. The dealer could not sell just a regulator but instead offered a new fan / regulator (expensive).

The original design does not allow enough surface area to adequately conduct heat away from the regulator and therefore the regulator malfunctions.

If you're lucky enough to find a regulator I suggest you do something similiar to what I did. Buy some conductive electronic paste at Radio Shack. Get some aluminum foil to increase heat transfer surface area and act as a heat-release-fin. Sandwich Aluminum fin between regulator and blower body. Smear heat conductive paste on all contact surfaces.

I did this two years ago and my system has not failed since.

Good luck.

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Neil
1997 E300D - naturally aspirated
280,000 miles (as of November 2015)

Here's a little more information for the record.

For the interim period that I was searching for a used regulator, I designed a simple pushbutton regulator bypass. My design allowed the A/c system to operate normally if the car was not too hot (because my blower would operate in low to medium speeds, just not high speeds). If I needed quick cooling then I would push the button and full voltage would go to the blower. Once the car was cool then I would push the button again and then the current was sent thru the regulator. The pushbutton was tiny and I routed to the back of the ashtray. My carpool members said it reminded them of a James Bond 007 movie.

Also, to help you diagnose the regulator as the problem. You can use a voltmeter to measure voltage coming from the pushbutton controller. It should vary each time you push a button to increase blower speed till a max voltage of 4.5 (I think). If you see that, then you know your pushbutton controller is fine.

If you pass the above test, then supply full voltage to the blower by bypassing (ie., jumping) the blower regulator. If the blower operated at high rpm then you know you have a regulator problem.

Hope this is clear enough and good luck.

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Neil
1997 E300D - naturally aspirated
280,000 miles (as of November 2015)

Michael B;

I found the interior cabin filter and was able to drop the panel you described. For other who try this, be careful with the release tabs, I broke one of them getting the panel loose.

My filter was moderately dirty. I ran the system with no filter and still no more flow. From other posts in this series, I beginning to think I have a regulator problem. I thought I read in another post that the regulator is on the negative side of the blower circuit, and can be checked by jumping the connection between the blower and regulator to ground. Does this sound correct?

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KCScout
98 S420 My Wife's Baby
97 S320 My road car
83 300D My old road car (love that diesel)
81 300SD Wife's former Baby
81 240D A fun stick shifter
71 220D My first one

Well I got a chance to bypass the regulator and voila, the fan immediatedly kicked into high gear. Guess I will start searching for a good price on a regulator. Anyone have any suggestions. The best price I have found so far is $212.55. I have also seen two brands at each vendor. The Behr is always more $$$$. Does anyone know why that is, and if there is a real quality difference I should be aware of.

Note: The cheaper unit looks just like the blown one in my car

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KCScout
98 S420 My Wife's Baby
97 S320 My road car
83 300D My old road car (love that diesel)
81 300SD Wife's former Baby
81 240D A fun stick shifter
71 220D My first one

kcscout:

I have the same problem with my 1994 S500. When I turn on the HVAC no fan / blower at any speed - min, auto, max. I have two questions however:

1st. How do you determine that it is in fact the regulator and not the blower itself. Previously described was a way to bypass the regulator - but how exactly is this done? I have yet to peak under the hood - but I assume that the regulator simply sits between the power supply and the blower itself - and that the circut can be easily completed by just removing the regulator from the line? By the way - Where are all of these components located? From what I understand they are on the passenger side of the vehicle close to where the engine bay meets the windshield?

2nd. where did you find a price of $212 for the regulator? the lowest that I've seen so far is $240.

Thank you!

dbs600;

You can get the blower regulator from Auto parts warehouse (***********************) they have the exact replacement for the $212.55 and an upgrade (Behr) for $242.69. I am still trying to find out if the upgraded unit is worth the extra money.

__________________
KCScout
98 S420 My Wife's Baby
97 S320 My road car
83 300D My old road car (love that diesel)
81 300SD Wife's former Baby
81 240D A fun stick shifter
71 220D My first one