Aux fans-what temp do they function on E420
 

Anybody know at what temp do the aux fans come on. I checked fuses and they are ok. It may be I just have not run car long enough and weather has not been that warm, to kick in fans. Anyway to check them out ? Thanks

High fan is 105/107 cut-in via coolant temp sender unit at thermostat neck. [ blue 2 pole]

Low fan is a/c high side pressure switch dependant.
Quick Fan circuit test is to jumper high pressure fan sw. at a/c drier. [ the sw with the 2 wire leads]

The later W124 chassis have fuses in the RELAYS for the aux fans. Remove the rear cover on the fuse box to access the relays. The blue relay is for the low speed fans & the green one is for high speed.

Thanks. I'll check this out. This is the small square box right behind the rectangular fuse box ?

There is also a fuse for the fans mounted separately from the fuse box (at least on the '93s). It's a 15-amp American-style fuse. I just replaced mine since my fans weren't coming on.

The 94/95-124 chassis have a fuse on top of each relay.
The high speed is a 15, but has been updated to a 25, and the low speed [ a/c pressure ] is a 30 A.
On the E320s , the high speed relay is blue [ slot C behind fuse box], the low is green [ slot B ]. This may differ on the E420, as the relays are switched in the CD.
One would think that the 30A circuit would be high fan, but the low fan circuit is the 30A due to the series resistor draw.

Arthur,
You are, as always, an incredible font of knowledge!

Do you have specs on the '93 model? I.E., do I also have fuses tucked away near the relays? And can I upgrade my "outside" 15A fuse to a 25A, since it does seem to blow with some regularity?

I checked the schematic on your 93-400e and the fuse for the relay feed is fuse #7 in the fuse box. This should be a 16A.
By relay feed , it means the low voltage side of the relay [ the coil that pulls the relay contacts in]
The load side of the relay [ fan motors] has an exterior 30A fuse. [F-22]
The 93 shows a K9 relay that combines the the low/hi fan contacts [ k1 and k2]
In 94, the 124.034/036 chassis went to the fuses on top of each relay. [ relay K9 and K10]

Which fuse are you blowing?

Arthur, thanks for the info. Now all I have to do is keep from dropping the screws into the dark abyss when removing the relay box cover.

It is easy if you use the full open hood feature. The back 4 screws are more accessible w/hood open all the way.....

No tsb that I am aware of, but if it is a seperate fuse than it should be high aux fan and can be increased. [I went with a 20].
They have found that high fan can draw as high as 25A.
The one that can't be changed is fuse 7 in the fuse box because that feeds not only the low side of the fan reay, but a bunch of other things. Plus the primary side of the fan relays draw is nil
anyway--
I would confirm this fuse to be high fan before doing the increase..
As I posted before. the later 124s [94/95 ] have placed these same fuses for both speeds on top of the relays. The high there calls for a 15, but it has been found to be to low to hold. The big draw on these fans [ and yours has the 2] is at start-up. Once they are running, the 15 is border-line, but start is when they crap.....

Arthur,
I have a separate, plastic 15A fuse and holder attached to the left front strut housing -- that's the one that keeps blowing.

I wonder if there might be a TSB about this like the one for blower motor fuses blowing and being upsized from 16 to 25 A.

Arthur, would 93 W124's have the same set-up as 94/95's?

1993's have the same engine #, VIN #, and chasis # as 94/95's, but because they were still called 300E's/ 400E's, they usually get ommitted.

The relay fuse location change became effective on MY 94.

I know what you mean with the 93 w/104, so the true test would be to pop the cover and look at yours in the flesh...
My info comes from a production change date on the a/c wiring schematics....
Won't be the first time things don't jive, but because the change is dated, I assume they have it right.
Let me know what you find....