A/C Low Fan not working - W140 M104 1995 S320 - PeachParts Mercedes-Benz Forum

JimF · #1 05-05-2006, 11:53 AM

Quote:

Originally Posted by 95 S320 LWB

Does it matter what sequence the resistors are wired? And what color wire they connect to?

I am assuming R15 in the diagram is part number 0001583745? (and that R15/1 is part number 0001583945)

Do you know which color wire that should be connected to R15 and to R15/1?

I just want to make sure I do this right the first time...THANKS!

As MB Doc said, it's a series circuit. To see this 'visually', look at Menu#18 to the sketch just above the "blue" table (Aux Fans Activation).

The first sketch shows a 'three-speed' system; if you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar.

The second sketch shows the 'two-speed' system. Note the jumper bar and only two wires. . . a 'series' circuit.

The resistors are switched in (shown in the schematic) with the Aux Fans according to the following;
"no-resistors-in-series" = High speed
"one-resistor-in-series" = Medium speed
"two-resistors-in-series" = Low speed

95 S320 LWB · #2 05-06-2006, 06:40 PM

I removed the old tube resistor - easy to cut and remove. The new resistors were the same length as the two bolt pattern where they are to be mounted. I removed the plastic cover in front of the fans and took out the old resistor.

Phil did not have the mounting plate from mercedes, so I went to radio shack and got a project board. I cut the board on my table saw, and then painted it black. I drilled holes to match the patterns of the resistors. I mounted the right-hand resistor to the project board using lock washer/nut and bolt. The left-hand one used the original mounting scres to mount to the board and to the frame. The connectors I made using crimped and soldered wire.

Anyway, all in - turned on the car, let it get up to operating temp, switched on the a/c and after about 1-2 minutes, the fans came on at low speed! Cool...

Thanks again MB Doc and JimF for your help. This board is the best.

JimF · #3 05-06-2006, 07:07 PM

Nice job . . . and good pics. MB Doc will hire you!

Larry Delor · #4 05-06-2006, 10:00 PM

Nice Job! (2 thumbs up!)

Seeing those pictures brings up the following...

Since the location of my resistor is not as handy as in the ones in the W140, is it ok to relocate the resistor? In Andrew's pictures, he has them outfront...pretty much exposed to the elements. Do the resistors care if there is a downpour (we tend to get those here in FL)?

Naturally, I would use wire that would a be a gauge larger than what MB would use (just to be on the safe side).

thanks!

-Larry

JimF · #5 05-06-2006, 11:23 PM

It's probably obvious but the reason they are mounted in front is the high power dissipation and the 'air' is need to keep them from overheating.

I would suggest you put them in that general vicinity.

As an aside, the "pc-board" will get a brown spot . . . actually two (2) brown spots after awhile.

mbdoc · #6 05-08-2006, 09:16 AM

OVERHEATING was a problem on any ballast resistor..The one on the 1992 & later 400E's & E420"s always had problems with the wiring harness getting too hot.. that location on the W140 chass is a much better placement.

vitop · #7 06-03-2018, 11:27 AM

Quote:

Originally Posted by JimF

As MB Doc said, it's a series circuit. To see this 'visually', look at Menu#18 to the sketch just above the "blue" table (Aux Fans Activation).

The first sketch shows a 'three-speed' system; if you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar.

The second sketch shows the 'two-speed' system. Note the jumper bar and only two wires. . . a 'series' circuit.

The resistors are switched in (shown in the schematic) with the Aux Fans according to the following;
"no-resistors-in-series" = High speed
"one-resistor-in-series" = Medium speed
"two-resistors-in-series" = Low speed

I have a really basic question.

How do you know if you have a two speed or three speed system?

JimF · #8 06-03-2018, 02:41 PM

"The first sketch shows a 'three-speed' system; if you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar."

The key is the "EXTRA" wire that the 2 speed systems don't have. If you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar.

Another way: on a HOT day, idle the car with the AC on and hood closed. The engine s/b COLD. After a while you should hear the Aux Fans increase in speed (2nd speed) and then, as the engine temp climbs, the A/F will switch to high speed.

But the easiest way is to look for the wire between R15 and R15/1.

vitop · #9 06-03-2018, 03:05 PM

Quote:

Originally Posted by JimF

"The first sketch shows a 'three-speed' system; if you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar."

The key is the "EXTRA" wire that the 2 speed systems don't have. If you look carefully you'll see an 'extra' wire that goes to R15 resistor. There's no "jumper" bar.

Another way: on a HOT day, idle the car with the AC on and hood closed. The engine s/b COLD. After a while you should hear the Aux Fans increase in speed (2nd speed) and then, as the engine temp climbs, the A/F will switch to high speed.

But the easiest way is to look for the wire between R15 and R15/1.

Thanks Jim:

I'll look. For some reason I thought I had that other version of the resistor that is part of the wiring harness. I'll check it out again. Either way, the fans are not coming on and I need to figure out what is going on (or in this case, not going on)