I have a 92 400E. Auxiliary fan does not turn on whae it should (either while AC is on or when engine gets over 105C). I have tested the fans and they function, so issue is elswhere. I have been going nuts trying to find a schematic with no success, so if anyone could help with that, thanks in advance. Here is what I have found so far. The wire that connects to the top of the preresistor was rusted in half. Looks like the preresistor is shorted (o hms) so ordered a new one. I think i messed something up by following some advice I recieved in a post by shorting together the wires that went to either side of the preresistor (taking the resistor out of the circut). Fan turned for a second but heard someting pop in the area of the fuse box (fan stopped turning, expect without the resistor, it turned fast and drew too much current?) but was unable to find anything blown. Some questions...

1. Are there any fuses between 12v and the preresistor? If so where?
2. Is it possible that I blew the relay? Is it fused?
3. Are there online schematics or somethig I can reference?

Look forward to some help.

 

As another newbie I am not sure I can help.

The following pertains to my 93 300e 4matic. I apologize if does not apply to your 400e.

I just replied to another thread about my radiator fan issue. The fans on my car are pulling way to much current. When wired normally the fuse that blows also runs the driver window and sunroof I believe.

If everything in your interior is still working, then it is likely a problem other than in the fuse box. I saw another post mentioning a fan motor issue where the owner pulled the motor winding and corrected his issue without removing the fans. Also mentioned bearing issue but I believe you stated that you fans turn freely.

 

Hi Joel,

Sounds like a different issue. I would look at the aux fan relay. The fuse in the fuse box (at least in the 400e) is specifaclly for the relay. The lager fuse (30 amp) is for the aux fan circut.

This is getting more odd as I venture further. This morning I replaced the 30 amp fuse, and the relay with no change.

So, if I turn on the key with the AC on max with the AC pressure snesor (red) jumpered, the relay closes but the fan does not turn. I know the fans work becuase I can manually close the second relay (which normally closes when the engine temp exceeds a certain temp) and the fans turn on full speed. The pre-resistor is brand new, the relay and the fuse are brand new and the AC pressure switch is jumpered. What am I missing??

 

I had a problem with the fans and my '92 400E. The fan's relays would get over-heated and the fans would stop turning. The mechanic I had said the problem was the fans themselves and I could get new relays, but that wouldn't fix the problem. He was right. Good luck

 

I had a problem with the fans and my '92 400E. The fan's relays would get over-heated and the fans would stop turning. The mechanic I had said the problem was the fans themselves and I could get new relays, but that wouldn't fix the problem. He was right. Good luck.

 

Thanks Patricia. My problem is that the fans never start up in the first place. It's getting more complicated as I have replaced the relay and the fuse. I can manually activate the relay and the fans turn *high speed "temp circuit) but the low speed circuit (for the air conditioner) is where the problem is. When I jump the AC pressure connector, turn on the AC and turn the key, the relay engages but I never get 12v to the pre-resistor (which is also new).

If I wasn't already bald, this would definitely be a hair thinning excersize. Thankfully, fall is here and the 90 + days are gone, so I have some time.