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-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 08-10-2012, 04:58 PM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
1991 350SD - Electric fan running all the time

As soon as you turn the key to the run position, the left (driver side) fan starts running at ful blast and wont turn off when the car is running.

Any ideas?

__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #2  
Old 08-10-2012, 06:59 PM
Registered User
 
Join Date: Aug 2007
Posts: 972
Stuck relay.
Reply With Quote
  #3  
Old 08-10-2012, 09:27 PM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
Hmmm, possible, possible.

I was wondering if the PO wired it direct, but I didn't have this problem before the engine swap. But I touched nothing in that area. I guess it could be a coincidence.
__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #4  
Old 08-11-2012, 10:02 AM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
Any idea where the offending relay is located? Fuse box?
__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #5  
Old 08-11-2012, 01:40 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,841
Yes.

Sixto
87 300D^2
Reply With Quote
  #6  
Old 08-11-2012, 05:08 PM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
The relay was identified, and seems to be good (pulled the cover, and circuit is open) called my father to check with him. He said to study the harness differences in the 300 vs the 350. He said a sensor is pushing the current to the relay, I need to track that down. Never ran into this on any of the other 300 to 350 swaps. But, this IS the first 91 I've swapped into. All others have been 90's and SDL's, not SD's for whatever that's worth.
__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #7  
Old 08-11-2012, 05:18 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,841
The fans run in parallel so whatever triggers the left fan triggers the right fan simultaneously. Either the left fan is stuck on in isolation, or a sensor is stuck and the right fan is dead.

If there's a 3-pole temp switch on the turret fitting for the upper radiator hose, remove the connectors and see if the fan turns off. If so, the temp switch and the right fan are bad. Or your engine is overheating

If there's a temp switch with connectors on pigtails on the AC receiver/dryer, remove the connectors and see if the fan turns off. This temp switch taps into the refrigerant circuit so don't remove it without first discharging the AC system.

Those are the fan triggers on an 86-87 SDL. The 90-91 SD/SDL might be different.

Sixto
87 300D^2
Reply With Quote
  #8  
Old 08-11-2012, 05:37 PM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
I was mistaken. Both fans are running full bore. I couldn't see that well the other night when I observed it.
__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #9  
Old 08-11-2012, 06:24 PM
Registered User
 
Join Date: Feb 2009
Location: Roanoke, VA
Posts: 833
Disconnected high pressure switch on dryer, cycle switch, 3 pole upper hose wiring, cruise control (it was handy) all at once, both fans still blaring. I dont recall this happening. There is a sensor under the injector lines screwing into the head, but I think that's just the sender for the gauge.
__________________
1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D
Reply With Quote
  #10  
Old 08-11-2012, 09:58 PM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,978
I have this exact problem in my E300D W124 - the fans switch on full when the engine is cold and the ambient is warm. They do shut off when the engine comes to normal temperature. But the relay clicks about 10 times in rapid sequence when it shuts off

The other bit I have noticed is that if the ambient is about 75 degrees - they dont switch on.

The blue temp sensor that goes to the HVAC PBU which actually controls the high speed function of the fans - shows correct resistance and when the fans shut off engine running - when I disconnect the plug to the sensor the fans work high speed just as they would normally.

I would have to dig into the dashboard to test the wiring and see whats wrong. Some people say the sensor goes bad and causes this while a dodgy PBU also causes this - but my HVAC works perfectly.
__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
Reply With Quote
  #11  
Old 08-11-2012, 11:27 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,841
Quote:
Originally Posted by jusme View Post
There is a sensor under the injector lines screwing into the head, but I think that's just the sender for the gauge.
Correct. If there's a temp sensor beside it it's for the afterglow relay.

Sixto
87 300D^2

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




All times are GMT -4. The time now is 04:58 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page