Interesting....

I just installed a new Servo, new Aux. Water Pump and Amplifier. The system worked perfectly for about 30 minutes, then blew the #3 fuse. It will ONLY blow the fuse in the defrost position.

In the interest of testing, I unplugged the servo, auxilliary water pump, resistance group, amplifier and blower motor, and the fuse still blows instantly.

I looked for shorts and found none. This car is unmolested, so the wiring is pristine.

When I unhooked the GRAY wire from the back of the pushbutton unit, the fuse stopped blowing. I soon discovered a 5 pole metal relay behind the glovebox. When I unplug this relay, I can re-connect the GRAY wire at the pushbutton unit and the fuse will not blow. When I re-connect the relay, the #3 fuse blows instantly.

I have looked at the wiring diagram and wonder if my pushbutton control unit could have a short in it????

I can't find anything else suspect thus far.

Any ideas?????

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Low Pressure A/C Compressor Cut-Off Switch (on receiver/drier) was shorted to ground....

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

On the 116, there is a 5 pole, metal-case relay, directly behind the glovebox. It controls the blower motor. If you wiggle the relay, often the blower motor will speed up.

Adding a 12 ga. ground wire from the realy mounting screw to the metal body will reduce the blower motor's amperage draw.

NOTE: On my 116.120, there is a brown graound wire that exits the harness and grounds to the screw that mounts the relay AND continues into the harness. Other 116's I have seen DO NOT have a ground wire "loop" to the relay mounting screw and instead, ground the relay elsewhere in the harness.

With the blower running, wiggle the plug-in. IF the blower speed increases, you have either a broken solder joint on the circuit boards AND/OR the double contacts in the relay are dirty or making poor contact.

Mine were badly mis-aligned. Correcting this mis-alignment and sanding the contacts REDUCED blower motor amperage draw.

On my 116.120 and others I have seen the rear journal on the blower fan motor is exposed and can be seen spinning when the blower is operating. I aded a few drops of sewing machine oil to this area, which was immediately drawn into the spinning shaft/buhsing interface.

The blower motor immediately increased in rpm and amperage was again reduced.

My blower is the original unit and it is only drawing 14.7 amps in the defrost position.

Hope this helps...Robert

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Very important piece of information there, almost worth a thread with an obvious searchable title of its own. Lots of blower motor problems on 116's documented here

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Hope this helps fellow 116 owners...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

This system works amazingly well when everything is correct. One of the big problems with lazy, sluggish temperature changes or varying back and forth between hot and cold, is the absence of the foam tube from the blower case to the in-car temp sender.

A section of 1/2" plumbing insulation is a cheap and reliable fix!!!!!

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership