I replaced a leaky a/c hose in a friend's 97 E320 - it was a massive leak. The system calls for 33.5 oz of R134a. After vacuuming for 2 hours I only have 2 cans in there now (24 oz.) and the high pressure is already over 400psi. I found the problem: the aux fan is not kicking in at all. Ever. I watched the gauge start climbing towards 425 and no fan, so I shut it off.

I'm guessing the old hose sprung a leak due to excessive pressures when idling.

I did a search, and there is plenty on the W124, but I can't find much of anything on the W210 aux fan. Where do I start?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

First, ensure that the fan turns freely by hand (turning the exposed left-side blade should turn the right). If not, you know the problem.

Second, check the fuse in the box at the left-rear under the hood. Gassers have a fuse there for the fan; check the card.

Third, apply power to the fan motor directly from the battery and see if it turns. If not, you know the problem. If so, you need to suspect the controller (N65/1, I think).

See this thread:
http://www.peachparts.com/shopforum/showthread.php?t=75494

That thread deals with N65 mainly (but mentions N65/1) so you might want to also search for threads mentioning N65/1, which I believe is used in that car.

OK, I just went out there and looked for a fuse in the fusebox - there is none there, so I assume the car has the aux fan control module?

I also jumpered the fan using some house wire connected at the other end to the jump start terminal and ground (I tested with my VOM to make sure everything was hot). The fan did not spin up.

Can someone verify that I jumpered it at the right location? It is the 2-wire heavy gauge plug located right next to the high pressure fitting under the dust cap right in front of the condensor. When I replaced the condensor last year I recall the whole fan unit came out in one piece and the only electrical connection going to it was this plug. So I'm assuming that's the one that needs to be jumpered.

Again, no results when jumpering (if that's the right place to do it). Can I assume the fan unit is dead?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

That's the right connector. There aren't any other wires right by the AC high-pressure fitting.

The motor is on the left, and the right side is a pully-driven idler, so you only need to replace the motor and left blade. Phil (Buy Parts, above) has it for $205, if it's the same as the one in my car, and the installation is pretty easy. Get a new belt while you're ordering. He has an aftermarket dual-motor fan assembly which is probably better than the piece of junk I bought on Ebay, but it does cost more than the OEM motor.

OEM Motor:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1V816REW81VE0MO2A2&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1997&product=G5000-70034&application=000256294
Belt:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1V816REW81VE0MO2A2&year=1997&make=MB&model=E-320-002&category=W&part=Fan+Drive+Belt

OK, thanks for the info. I think there's another problem though. I had my wife start the car and watched my gauges. When the A/C high side hit about 375 I stuck my VOM into the harness for the fan, and there is no voltage! I watched until the gauge passed 400, then had her shut it off quickly. So over 400 psi and no voltage to the fan pigtail? Does that mean the controller module is shot? Where is it and how do I test it?

Is THIS it?

I think it's obvious that the fan is shot if it won't come on when jumpered, but even if I slap a new fan in there it looks like it won't be turning on without voltage.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Here's a better test.

Put the key in position 2, engine not running.

Hold both AUTO buttons on the pushbutton module for more than ten seconds (takes about twelve on my car) to put it in fan test mode.

Hold the REST button for more than five seconds until the display changes, then use the left AUTO button to change the display until the left side reads 20. The right side should read 10. If not, hold the AUTO buttons again for longer, then change the left side back to 20 (you would probably have moved it when putting the unit into fan test mode). 20 is the control current for the auxiliary fan, and 10 is full power.

Now hook a voltmeter to the pins with the fan disconnected. You should not see full power on that connector. You should see a bunch of voltage spikes for about a half-second, about every six seconds. If you see no voltage at all, the fan control module is likely dead. If you see these spikes, your fan control module still may be bad, but at least you have a hope of it working.

I can't say for sure that you have the part listed in the link. That's a picture of N65/1, and it's located behind the left headlight, if you have it. My car has the N65, which is in the fusebox under the hood, but performs the same function. Newer models use a completely different system.

Thanks, that's really helpful. I will run out there in a few minutes and try what you have suggested. In doing a search, I did read about the module located behind the headlight. I looked back there, but there is only bare sheetmetal between the R/D and the headlight. Also, in looking at the eBay part, it says it's only for 99 to 02 cars (this is a 97) so it's possible I don't have one.

Where exactly is the newer module located in the fuse box?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

It's the older module that's in the fusebox. N65 was replaced by N65/1, which was replaced by N76 and a new combination-control module N10-1 (hopefully you don't need these to repair this car).

You can see it if you take the cover off of the fusebox. Open the lid, and there are two screws inside with the fuses, and an additional screw at each corner (six screws in all). The module is right behind the fuse blocks, on the left side of the box (toward the fender).

Man, this info is awesome. I'm going to do some poking around and will report back. Thanks again!

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

OK, I just ran the test. I get a very brief power spike every 9 seconds or so. Does that mean the replacement fan should work?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

It means that you have a hope of it working. I'd try the new motor, since you know that you need one.

The spikes are the controller attempting to start the fan, but it detects no feedback, and kills the power. If you had a working fan motor, those spikes would start the fan turning, and after a second or two, full power would be applied.