Resealed my AC yesterday, aux fan fails while I'm charging the system today. Thankfully I caught this in time before there was any damage.

What happens is that is the fan shorts, and it's only on low speed, the low speed resistor limits the current enough to keep the fuse from blowing, but gets extremely hot. The resistor also happens to be in a spot where lots of leaves and twigs tend to gather. Bad combo. I caught a small fire down there because I was charging my AC system, it would have been far worse if I was driving.

There's a simple fix for this. Bypass the low speed circuit, so that the fan always comes on high speed if needed. This is pretty much desirable if you live in a hot climate anyway. If the fan shorts while on high speed, it will instantly blow the fuse.

Simply remove relay D, and connect it's coil input to relay C's coil input.

Aux fan resistor. FIRE HAZARD!!!


Low speed relay eliminated, bridged to high speed.


Wiring diagram...

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Ich liebe meine Autos!

1991 Mercedes-Benz 560SEL | Megasquirt MS3-Pro | 722.6 transmission w/ AMG paddles | Feind Motorsports Sway Bar | Stinger VIP Radar | AntiLaser Priority | PLX Wideband O2 | 150A Alternator | Cat Delete
1981 Mercedes-Benz 300SD | Blown engine, rebuilding someday...
1981 Mercedes-Benz 300SD | Rear ended, retired in garage.
2009 Yamaha AR230HO | Das Boot

Excessive speeding? It ain't excessive till I redline!