What turns on the aux fans? '96 E300D (OM606)

[Jeremy5848]

My wife came home in the E300D and I noticed that the left (driver's side) electric aux fan was running, although the engine was not that warm -- between 80C and 90C, maybe. It got me wondering, what triggers these two fans? a/c line pressure? coolant temp? moon phase?

I know that the OM603 engine in the W124 car has a single two-speed fan that is switched on in low speed by the a/c and high speed by the coolant temp (did I get that right?) but the '96 E300D is the first car I've had that has two electric fans in addition to the mechanical fan with clutch.

I did some searching . . . there are four pages of threads for "aux fan" and one for "auxiliary fan" but few posters bother to say which car/engine they were writing about and I didn't feel like reading each one.

I ask this strictly out of curiosity -- I am not, nor have I ever been, a member of the Overheating Party of the USA.

Edit: It appears that the right (passenger side) fan is driven from the left fan by a belt . . . and my belt is missing, hence only one fan works. I'd still like to know what circumstances cause the fans to work, though.

Jeremy

[compress ignite]

The climate control has both pressure and heat sensors...over temp will activate
the low speed fans.
Engine over temp will activate high speed on the fans.

[Matt L]

You need both fans, so replace that belt. It's a very cheap part and fairly easy to install. Also, I've heard one case of a thrown belt damaging the condenser.

The fan is variable speed, controlled with pulse-width modulation. The climate-control pushbutton unit N22 demands the fan if the refrigerant pressure or temperature or engine coolant temperature reach certain thresholds. There are multiple thresholds for each, and the fan runs at a higher speed as higher thresholds are reached.

N22 sends a signal to the pulse module N65 which actually supplies the power to the fan. At least this is likely to be the case on your '96. Other parts were used for this job over the years.

[Jeremy5848]

Thanks, guys, I'll replace the belt ASAP.

[Jeremy5848]

Now that I have the new fan belt ($7 from FastLane or ********AZ), I pulled the fan assembly (not really necessary to change the belt but a nice opportunity to pressure-wash the radiator) and discovered . . . the original fan belt sitting jammed between the fans and the radiator (a/c condenser, I mean). It had come off of the pulleys and was just sitting there. It was also rock-hard from age so I tossed it and installed the new one. It stretches and pops on easily. The fan belt (a Continental product, as in Conti tires) is tiny, only the size of a big rubber band (but longer) -- glad I didn't pay the dealer $25 for it.

Both aux fans now run together as they were supposed to. Wonder what I'll discover next?

Jeremy

[Matt L]

I don't think it really is practical to attempt to install the belt without removing the fan assembly, and the fan is easy to get it out.

The old belt is always hanging out in there. I read of one person who had the old belt puncture the condenser.

[mikemass1221]

what's the part # for that fan belt? I need one too. When I search it in fastlanes, I come up with a "multi-rib-belt" for $8.00 and change. Is this is?

[KarTek]

Belt P/N is:

011 997 00 92

This one:

http://catalog.peachparts.com/item.wws?sku=W0133-1638228&itempk=78218&mfr=ContiTech&weight=0.05

[mikemass1221]

TY