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

LinkBack Thread Tools Display Modes
Old 05-20-2002, 12:23 AM
Registered User
Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
Lost Tach and A/C

The Tach and A/C compressor in my 1985 300SD have finally stopped working completely. For the past year the problem has been intermittent -- when the tach would stop working the A/C compressor would disengage. I searched this forum and found a thread from 1999 that discussed two possibilities. 1) a blown fuse on the overvoltage relay and 2) loose wire that connects to the positive lead of the battery to the EGR control circuit. I have checked both of these and they are OK. Tach and A/C are still dead.

Anyone have any ideas?


Reply With Quote
Old 05-20-2002, 08:08 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
If the EGR computer IS powering up then the crank sensor(flywheel) must generate at least 5V ac current at idle for the system to operate properly.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator
Reply With Quote
Old 05-20-2002, 07:19 PM
Registered User
Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
I disconnected the engine speed sensor at the connector behind the first firewall and measured the voltage. With the engine at idle speed in read about 25mv. The reading did not change significantly when increasing the engine speed. Do I have a bum sensor?

Reply With Quote
Old 05-30-2002, 11:03 PM
Registered User
Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
Bingo!!! I finally got around to replacing the engine speed sensor. The tach and AC now work perfectly -- just in time for a hot Kansas summer. Thanks for your help.

Reply With Quote


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 12:09 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page