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1995 S500 coupe, 1990 Mazda Miata
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Discussion Starter #1
Has anybody done the upgrade from the original (A000 158 40 45) resistor? Originally, the resistor is a tube looking aparatus with a 2 wire harness that is made on to it and is bolted at the bottom of the fans towards the passenger side. EPC shows a multiple supercession to two resistors (A000 158 37 45 and A000 158 39 45), a "cable shoe", A002 546 30 40, a bracket that apparently holds the resistors, A140 620 71 14, and nuts and bolts to put it together. I can't find difinitive info on how to wire it. The service manual says to cut the lead off of the old resistor, but then states that the new resitor is supplied with a lead as a replacement (the cable shoe?), saying to route the lead behind the LH headlight and connect it with a 2 pin connector. I don't see that connector or any connector all the way to the fuse box where it's wired to the relays. I'm to go ahead and order parts as even with the A/C on the fans don't come on at all until the the temp is 107°C, but the info is vague.
 

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1995 S500 coupe, 1990 Mazda Miata
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694 Posts
Discussion Starter #2
Looks like nobody's been down this road? I ordered parts, and as described I got two resistors, a bracket and a short metal bar to jump the two resistors, basically hooking them in series. I'm not sure why Mercedes superceeded the original one piece, tube shaped solid state resistor (part number A000 158 40 45) with two resistors which are the coil and ceramic style, except maybe because of durability issues. The replacement resistors are a little different, and the schematic shows the R15 goes first and the brown & green wire being "in" and the blue & gray as "return". Again, I don't know if that matters. I'm going to install them Saturday and post the results. Hopefully with the A/C at 16 bar pressure, regardless of engine temps, I'll have low speed fans on.
 

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1995 S500 coupe, 1990 Mazda Miata
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694 Posts
Discussion Starter #3
Well, hooked it up yesterday, and now the fans do cycle, for about 10 or 15seconds, with the A/C on. I took it to work and hooked up gauges to the A/C and discovered that system works as it should, on at about 16 bar and that the fans are very effective in reducing head pressures. One scary note; the wiring to the aux fan resistor (which tested open btw) on the original was made onto the resistor, and both wires suffered from soybeanitis. One (gray/blue) went to a wierd crimp and solder connection behind the left headlight, and the other (brown/green) to pin 1 on the relay in the underhood fuse box. Every other wire in the loom was fine; no cracking and very pliable. The car has a replaced engine harness and I replaced the lower so hopefully that's all the defective wiring. Sorry no pictures; I'm camera challenged.
 

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1995 S 420, 2012 GLK 350 and 1997 Audi Cabrio; Previously 1982 280CE, 1974 450SL, 1974 911S Targa
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456 Posts
Has anybody done the upgrade from the original (A000 158 40 45) resistor? Originally, the resistor is a tube looking aparatus with a 2 wire harness that is made on to it and is bolted at the bottom of the fans towards the passenger side. EPC shows a multiple supercession to two resistors (A000 158 37 45 and A000 158 39 45), a "cable shoe", A002 546 30 40, a bracket that apparently holds the resistors, A140 620 71 14, and nuts and bolts to put it together. I can't find difinitive info on how to wire it. The service manual says to cut the lead off of the old resistor, but then states that the new resitor is supplied with a lead as a replacement (the cable shoe?), saying to route the lead behind the LH headlight and connect it with a 2 pin connector. I don't see that connector or any connector all the way to the fuse box where it's wired to the relays. I'm to go ahead and order parts as even with the A/C on the fans don't come on at all until the the temp is 107°C, but the info is vague.
so...let's see...your parts list was...

-000 158 37 45
-000 158 39 45
-002 546 30 40
-140 620 71 14

Was there a service bulletin detailing this "upgrade"...and is it the same for a S420/S500 sedan?
 

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1995 S500 coupe, 1990 Mazda Miata
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694 Posts
Discussion Starter #5
I never found a service bulletin explaining the change-over, but I did find where Mercedes decided to go to a 2 phase (2 speed) system instead of three. The parts list comes up in EPC when you look up the resistor. The original, tube shaped sealed resistor has been superceeded. The problem I ran into is testing the original style, as it's hard wired into the harness. I would think that you can't read resistance properly as it would back feed through the electrical system, so you would have to cut the wires and later resolder to test it.
 
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