My electric fans do not come on at all in either low or high.

To check out the low side, I jumpered the white pigtail wires at the receiver/dryer and I can hear the fan relay clicking. I can also trace 12 volts down from the 30 amp strip fuse near the fuse box to the dropping resistor behind the front left headlight. I'm getting 12 volts on both sides with the ignition on.

On the high side, when I pull the temp sensor (shown in picture) off the intake manifold with the car running, the fans do not come on.

Any ideas?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Bring a jumper from Bat pos+ to the R15 dropping resistor.
Jumper to terminal with single wire side is Low fan, other 2 wire side is High.
Key does not have to be On for this test.
If NO fans, the problem is the fan motor/s or a bad wire connector between the R15 and fan motor/s.

If YES ..you have fans w/jumper, then procede below:

That chassis had an aux fan circuit relay change mid '94 production. The early has a single relay for both low/high fan with the F22 30A fuse. The later series switched to individual relays ..one for High and one for Low. These are in the relay box behind the fuses. Have to take a few screws to get to it. [ full open hood position].
You will know right away b/c those seperate relays are 1 green and 1 blu. They will have a spade fuse on top of each relay. That fuse is the load side of the relay cicuit and is suspect.
B/c you can hear the relays clicking, you know you have power to the coil side of the relays, [ from fuse #7] so it is the load side that is bad, meaning the fuses on top.
Check and see if you have the newer set-up. If YES, then check those fuses [ One 15 and one 30}.. While you are there , there has also been a Benz upgrade for the low fan fuse to 25A from the orig 15A.

Post results.

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A Dalton

Thanks, Arthur. I was hoping you would come to the rescue. I will try running a separate 12 volt source like you suggested. When I use a voltmeter and put one lead on a ground and another to the dropping resistor (either side), I am readying 12 volts. So there is voltage on both sides of the resistor.

Also, I pulled the relay box earlier an I did see a relay like you described with a Delco-type spade fuse on the top. I'll check it again tonight. If I'm getting 12 volts to the resistor, doesn't that run directly to the fans or does it go back to the relay box in between?

Should the fans come on high when I pull the temp sensor in the picture above?

I'm thinking it's a bad connection between the resistor and the fans but I can't see where the fan wires run as they come out of the fans.

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

If you have 12v at R15, then you most likely have a wiring connection problem down-stream from R15.
But a meter can fool you if there is no load.

That is why I suggest the bat jumper to assure a full 12v direct. This test is the same as if you had taken the fans out and did a Bench test...but this makes that same conclusion w/o that hassle..
I would also wiggle the wires on R15 where the two wires come to that terminal.. it is common to have a poor connection right there and that connection will effect both high/low feed. That connection suffers from heat fatique from R15 being ceramic and a High heat source.

Another test for relay feed is to put your test lamp [ or meter]on that R15 terminal and then jumper the drier switch for low fan and unplug blu sensor for high and see if that test lamp lights ..[ or meter reads] each time you do each test. That will verify relay circuits. Key must be ON for that test.
If YES, then give the fans a spin by hand [ there is a rotation/direction indicator arrow on the hub]..or give a light rap on the front hub.....
This is not a complicated circuit. Most guys get confused b/c they do not realize that the low and high fans are completely seperate circuits, and the only thing they have in common is the fan motors themselves.
High fan is Coolant temp sensed and low fan is a/c high side pressure sensed..nothing to do with one another.
Here is where the fan connector is:
http://catalog.peachparts.com/ShopByVehicle.epc?q=1994-Mercedes--Benz-E4--0-Cooling--System&yearid=1994%40%401994&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6396%3AMBC%7C1530%3AED%7C10000072%40%40E420&catid=240909%40%40Cooling+System&subcatid=240990@@Auxiliary+Fan+Assembly&mode=PA

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A Dalton

THANK YOU, ARTHUR!

You were absolutely correct. I had two blown fuses--one on each relay. I replaced them both (upgraded to 25A for the low fan too) and they work fine in low and high. With the engine running, I pulled the harness off the coolant sensor on the intake manifold and they shifted right to high. Why I was getting 12V at the resistor when I measured it is beyond me, but I'm not going to look a gift horse in the mouth.

I think I know why they both blew. A few days ago, the radiator broke where the upper hose attaches and all the coolant came out. I'm thinking the water caused a short that took out the fuses.


Thanks again for your help. This forum is great.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Whatever the original fuse values were I be would using that. Upgrading to a higher value is playing with fire - literally.
You could find some other electrical piece of equipment becoming the fuse rather than the safety item itself.
Make sure all fuses are copper. Remove all fuses from the box and make sure there is no corrosion or "film" covering the contacts.

I will take his word for it. Arthur has probably been right more times than anyone on this forum.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

'pologies for that and to Arthur

Very Good..

As you can see, you have the later/2nd generation relay system. And let me assure you that Benz has a TSB [ Technical Service Bulletin] on the upgrade of Low fan fuse protection. They found 15A to be border-line on the Low Fan circuit w/dual fans. Spec on pre-resistor circuit can reach as high as 22A on the Dual Fan equipped chassis and the 25A on that circuit is applicable and safe.
And as you know, these are the spade fuses , so you also do not have to be concerned with copper as they are not the Bullet type fuses Benz uses in the Fuse Box.

One other tip for you and readers.
I have many times seen these two relays inadventantly put back into the wrong sockets [ reversed]. It happens quite often , even by well intended Techs b/c the sockets will take either relay. So, what happens is the High Fan circuit winds up with the lower fuse value, and vica-vera. And one wonders why it keeps blowing the fuse. It is simply in the wrong slot. Something I always check first. You can suspect that condition if the low fan does work, but the high one does not and it consistantly blows it's fuse.. That is why Benz uses the 2 different colors. The simple verification is to remove the 30A fuse and pull the blu sensor plug. If you do not then have high fan, you know the relays are in the correct slots/not reversed.
Everything is simple once you know the system.

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A Dalton