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 06-27-2002, 01:06 PM
Registered User
 
Join Date: May 2000
Location: Georgetown, MA
Posts: 84
Auxiliary fan operation

In my 86 300E, the auxiliary fan does not come on when the temperature exceeds 115c. The fan works with direct power from the battery. There is power on the 30 terminal from fuse 7 and from fuse D on the K9 and K10 relay. Apparently the relay is not moving from the 87A to the 87 position because when I manually jump the 30 and the 87A the fan works. What am I missing? Are these relays prone to failure? The fan also works when I jump the high pressure switch. Any help would be appreciated.
JohnO
Reply With Quote
  #2  
Old 06-27-2002, 02:44 PM
LarryBible
Guest
 
Posts: n/a
Coolant temp is not what causes the aux fan to come on. High side A/C pressure causes the fan to come on to bring down excessive high side pressure to prevent A/C system damage. There is a high pressure switch, probably mounted on the filter drier.

If the A/C charge is a little low, the fan may not come on at all.

Good luck,
Reply With Quote
  #3  
Old 06-27-2002, 03:18 PM
Senior Member
 
Join Date: Apr 1999
Location: Walnut,CA,USA
Posts: 554
The auxiliary has two operating modes
Low speed activated by pressure switch at a\c drier pressure over 20bar with relay K10 and resistor.
High speed activated by temperature switch S25-5 at 105c coolant temperature with relay K9 without anyresistor.
__________________
MB STARS Master Guild Technician,17 years MB tech
14 years independent shop owner
Reply With Quote
  #4  
Old 06-27-2002, 04:19 PM
Registered User
 
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,777
You have high fan when jumping 30-87 and this is the load side of the K-9 relay, so the coil side of the relay is not pulling in or you have a bad relay.

You know you have power as the load fuse feeds both high/low speed fan. So the test is to ground br/gn wire at pin #2 at temp sensor for 105 cut-in. This completes coil side circuit for relay latch.
If high speed now comes on, change ETC sensor.

If it does not , you have a bad relay/open wire.....

I can send you the schematic , if needed
Reply With Quote
  #5  
Old 06-27-2002, 05:23 PM
Registered User
 
Join Date: May 2000
Location: Georgetown, MA
Posts: 84
Arthur, Thank you for the offer of schematics. I do have the MB Electrical Troubleshooting Manual. I agree with your diagnosis of a bad relay or an open wire. I forgot to mention that I jumped the temperature switch and the fan did not come on. Since both the K9 and K10 relays have the same part number, what role does the R15 auxiliary fan preresistor play? I do not remember seeing one when I traced and tested the wiring. Brutally hot and humid out and I do not think I will get back to troubleshooting this afternoon. I live across the border in MA. You know what I mean. Thanks for all the responses.
John O
Reply With Quote
  #6  
Old 06-27-2002, 05:29 PM
moedip
Guest
 
Posts: n/a
Not too sure on your car - but normally the fan will kick in low speed when one sensor activates ( hence the resistor) and kicks in at high speed when the other one activates - hope that helps.
Reply With Quote
  #7  
Old 06-27-2002, 06:14 PM
Registered User
 
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,777
The resistor simply allows K-10 to put the resistor in series with the fan circuit for the LOW speed [ a/c high pressure circuit]
This R is behind the drivers headlamp.
You can exchange the relay for the test of the High speed [ K-9] circuit.
You have to have a relay/ relay coil circuit fault because you stated the fan ran when jumpered 30/87.
And you know you have relay coil feed for both K-10 and K-9,
cuz they are the same fuse [7]. So the completion of the circuit is a switched ground [ This is what the ETC does].
My guess is open relay coil or coil pulling contacts in, but load contacts are burnt to point of non conduction.....
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 09:10 PM.


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