Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 06-17-2001, 09:55 PM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
Need some help with my A/C blower.

No matter where I set the 'volume' wheel (Min, AUTO, Max) it blows a very low volume of air. As the control is rotated from one end (Min) to the other (Max), the air volume changes but it's blowing at what would be considered a MIN setting.

The A/C is fine; compressor cycles and the evaporator temp ranges from 34F to 40F, so it's blowing very cold air but just not a lot of it!!

The sensors (internal temp and external temp sensors seem ok based on the readings of the using the DIAG mode (my page; menu #14)



Poked around and it seems to be this 'critter'. What is it?? Looks like a triac? But that's for AC? I'm confused?

Thanks in advance for any help.
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
  #2  
Old 06-17-2001, 10:41 PM
Registered User
 
Join Date: Dec 2000
Posts: 368
That little critter is your problem. It's the blower regulator. For some reason on the 140's they always go bad. They are fairly expensive $300-$400 at the dealership, $270 wholesale. Fastlane sells it for about $170, but I'm not sure if it's OE. They updated the part to 140-821-83-51. Make sure to get the new one unless you feel like changing it again in a couple of years.

Vinamg

Reply With Quote
  #3  
Old 06-18-2001, 02:53 AM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
Regulator . . .

Tnx Vinamg!

Do you know how it works? Can't find any data on my CD about anything for this circuit. Any info is appreciated.
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
  #4  
Old 06-18-2001, 06:36 AM
Registered User
 
Join Date: Dec 2000
Posts: 368
Jim,

Check out the following thread W140 Evaporator Core

Steve gives a good explination on how it works.

Vinamg


[Edited by vinamg on 06-18-2001 at 05:39 AM]
Reply With Quote
  #5  
Old 06-18-2001, 12:44 PM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
'big transistor' . . . .

Vinamg, tnx again!

Did a search but never came up with that thread. But I do understand completely how it operates, as an "emitter follower" amplifier. And how it can fail!

Here's how it can. Since it's controlling the power for the fan motor, it's must withstand a lot of power dissipation, thus the required heat sink to the blower's frame. Roughly here's the scenario: 13.8V (terminal 15) and 15amps (when the transistor is about 'half' on, yields about 90 watts dissipation. The transistor must dissipate the energy not transmitted to the blower. Thus when the fan is on MAX, the dissipation is minimal since the transistor passes all of the power to the blower.

Most people operate their cooling controls around halfway on so it's constantly dissipating a large amount of energy. So I can see how it can easily fail.

Thanks again for the great info.

One other point: recently somebody suggested using pictures to describe problems and/or their solutions. This to ease problem solving by making it easier for knowledgeable people to 'see' your problem. We all should do more of it.
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
  #6  
Old 06-18-2001, 01:18 PM
Registered User
 
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,777
>> One other point: recently somebody suggested using pictures to describe problems and/or their solutions. This to ease problem solving by making it easier for knowledgeable people to 'see' your problem. We all should do more of it.<<

For sure.

A pic is worth a hundred post.
Reply With Quote
  #7  
Old 06-18-2001, 04:33 PM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
A final post script!

Got the new part today for $140, MB dealer price $338!! Get my parts thru my tech so it saves a lot of $$$.

After taking the unit out and replacing with the new amplifier, I could see why the old one failed.

The unit is supposed to have a heat sink plate (3" long x 1.5" wide x 3/16" thick) attached to the bottom. My old unit did not. Also there was no silicon grease applied. So with the missing heat sink plate and no grease it's a wonder that it lasted as long as it did.

Tnx to all you knowledgeable Benz men!
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
  #8  
Old 06-18-2001, 05:51 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
As a corollary to what I said earlier, the control circuit uses 1 to 8v. The blower uses between 20 and 25 amps. The blower comes with a new regulator. A blower using too much current will give a short life to the regulator.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #9  
Old 06-19-2001, 04:18 AM
angbrian
Guest
 
Posts: n/a
does this apply to the 124 model?
if it does, would you mind telling where the little 'critter' is located?
Reply With Quote
  #10  
Old 06-19-2001, 08:42 AM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The blower regulator is under the motor, under the wipers on the 124 Chassis. The circuit does have an easy access three wire plug directly behind and above the brake booster.

The yellow wire gives the control signal 1-8v and the red carries the current (which can be measured with an inductive amp probe). We had one the other day that had a froze motor and when it was replaced it seemed to be too low of a speed. We monitored the control signal which rose and fell according to the the blower speed chosen but there was never more than 6amps through the red wire. Just to be sure we checked our shop wagen (91 300TE) and it got around 20amps through its blower. We replaced the regulator and all was well.
__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
  #11  
Old 06-21-2001, 02:12 AM
JimF's Avatar
'94 S500: only 793 sold!
 
Join Date: Mar 2001
Location: San Diego, CA
Posts: 1,925
a post script . . . .

Had to go into the El Cajon valley today, temp about 90+ deg! So the A/C got a good test.

The air was so cold that I had to turn the blower down to almost 'MIN' so I didn't get frost bite!

The evaporator temp cycles between 37 to 41 deg F. So it's really cold. Now's the time we really need a good A/C system.

Tnx again for the help.
__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low pressure valve A/C on 96 E320 bjafari Tech Help 1 07-09-2004 10:36 AM
What should high & low side pressure be for A/C? Ron Brooks Tech Help 4 07-05-2003 03:39 PM
Bad odor from A/C and Refrigerant leakage Holson Adi Tech Help 5 01-17-2003 03:00 PM
Need A/C pressures High and low for a 91 300E 3.0 DIYBenzer Tech Help 0 01-30-2002 10:15 PM
A/C low pressure compressor cut-off gkimbrough Tech Help 5 05-12-2000 07:52 PM



All times are GMT -4. The time now is 09:36 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page