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#1
05-20-2002, 12:23 AM
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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? Thanks, Bill 
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#2
05-20-2002, 08:08 AM
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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
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#3
05-20-2002, 07:19 PM
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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?
Bill
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