Parts Catalog Accessories Catalog Tech Info Tech Forums
 
  Search our site:    
 Cart  | Project List | Order Status | Help    


Go Back   PeachParts Mercedes ShopForum > Technical Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-24-2013, 04:37 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Monovalve short damaged PBU

My 85 was getting intermittent heat with the AC on max. In troubleshooting whether the monovalve was at fault I may have shorted the 2 pins in the monovalve connector, and the intermittent heat became permanent heat.

I determined that the monovalve was not getting a ground signal. Fuse 14 is ok so the monovalve is getting power, just not being grounded (by the PBU). Took the PBU out and traced the ground wire (brown) to pin 4 of the connector on the right in this pic

__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #2  
Old 07-24-2013, 04:39 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Took apart the PBU and found a burned trace from pin 4

__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #3  
Old 07-24-2013, 04:41 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Soldered a wire to jumper the burned trace

__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #4  
Old 07-24-2013, 04:45 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Put the unit back together and test. Light bulb connected across the monovalve is lighting up so it is getting a ground again. By turning the temp control dial to coldest detent click, monovalve is on constant (light on= no heat). Temp dial on hottest detent click monovalve is off (light off = full heat).

Still need to road test with AC on to make sure it works.

__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #5  
Old 07-24-2013, 04:49 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
I am surprised a short on the monovalve does not blow the fuse but blow the PBU instead. I think I will be adding a fuse to the monovalve to prevent this from happening again.
__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #6  
Old 07-24-2013, 06:30 PM
Jeremy5848's Avatar
Registered Biodiesel User
 
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 7,807
This has long been an aux pump problem with the W123's ACC but I've never heard of one involving the monovalve. You did a good job diagnosing and repairing. A fuse would be a good idea. The later ACC versions (W124) were built to be short-circuit resistant so MB must have gotten a lot of complaints.

Jeremy
__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . 214,000 miles My car
1996 E300D (W210) . 295,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . . . 678,685

"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
Reply With Quote
  #7  
Old 07-24-2013, 10:11 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
The fault was shorting the 2 monovalve wires together. Easy to do after taking the connector housing apart to squeeze the contacts to make them tighter forgetting the key is on.

Do you have a more legible copy of this diag.? Where did you find it?

http://i323.photobucket.com/albums/nn447/Jeremy5848/Mercedes%20Stuff/Schematic.jpg

I think the same thing happened on my 83 300D a few years ago. I posted about it but didn't document or take pics of the fix and had to figure it out all over again.
__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #8  
Old 07-25-2013, 01:07 AM
Jeremy5848's Avatar
Registered Biodiesel User
 
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 7,807
The diagram probably came from the W123 climate control manual, which I no longer own. Clicking on the link brings you a small copy of the diagram but my PC gives me a (+) magnifying glass symbol for the cursor; clicking that enlarges the diagram and it is very legible in the large size. I still have my copy of the file that I uploaded; it is 4446 X 4415 pixels and 1.88 MB in size so there should be no problems seeing all of the detail.

Jeremy
__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . 214,000 miles My car
1996 E300D (W210) . 295,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . . . 678,685

"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
Reply With Quote
  #9  
Old 07-25-2013, 01:30 AM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Quote:
Originally Posted by Jeremy5848 View Post
The diagram probably came from the W123 climate control manual, which I no longer own. Clicking on the link brings you a small copy of the diagram but my PC gives me a (+) magnifying glass symbol for the cursor; clicking that enlarges the diagram and it is very legible in the large size. I still have my copy of the file that I uploaded; it is 4446 X 4415 pixels and 1.88 MB in size so there should be no problems seeing all of the detail.

Jeremy
The jpg I downloaded from the link is only 700kb. Can you email me (in my profile) the orig hi rez file? Thanks
__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
Reply With Quote
  #10  
Old 07-25-2013, 01:42 AM
Jeremy5848's Avatar
Registered Biodiesel User
 
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 7,807
Tomorrow.
__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . 214,000 miles My car
1996 E300D (W210) . 295,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . . . 678,685

"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
Reply With Quote
  #11  
Old 07-28-2013, 02:00 PM
funola's Avatar
Registered User
 
Join Date: May 2005
Location: NYC
Posts: 4,947
Quote:
Originally Posted by Jeremy5848 View Post
Tomorrow.
Have you sent it? Good news is that the fix is working. With AC on, no more full heat through the vents. Hoses to the monovalve is cold = no flow.
__________________
85 300D turbo pristine w 157k
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parts for sale- pm me your needs.
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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 02:22 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, 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