A/C Auxiliary Fan Troubleshooting
 

It appears that the A/C auxiliary fan that forces air through the condenser (the one in front of the radiator fan) has quit. Can anybody give me some troubleshooting tips to confirm that it is actually the fan that is dead, and not a relay???

Thanks,

mike

Swapping relays is easy. The a/c and fan relays are located on the top, left wheel well. Silver cubes, possibly under a black plastic cover.
Or you could jump battery power to the fan.

Is your a/c working well? If not, that could explain the fan problem.

It might be the step down resistor. I believe it's tucked under the ABS pump behind the left headlight. It's a white ceramic block about 15mm by 15mm by 50mm with a wire attached to each end. It's easy to see if the resistance coil is burned or corroded. Wrecking yards are full of them or you can bridge the wire for full fan force.

Sixto
87 300D

I don't think the resistor is applicable to an '82 240D. Nor the ABS.

Verify the switch is getting voltage. If it's not getting voltage check fuses and relays. If it is getting voltage jump out the pressure switch and the fan should run.
If it doesn't run the fan is bad.
If it does run it may be the switch. Or it may be undercharged.

Danny

I'm Answering Whatever i can in hopes of building up my Karma Bank for a question that i need answered.

The Aux Fan is intended for cooling the a/c condenser. So if your a/c is non functioning, then the aux fan has no purpose. If your a/c is functioning it's probably a good idea to have a working aux fan.

Two things to try:

1. The aux fan is controlled by the refrigerant temperature. The temp sensor, along with the pressure sensor is located screwed on to the receiver/dryer. Pull the Connections on the temp sensor and hook them together. With the two wires hooked directly to each other the fan should kick on when the key is on.

2. Test the Fan independently. The aux fan is connected more or less underneath the drivers side headlight. Trace the wires from the fan.. down in front of the condenser.. under the radiator.. back and down a little further and... you'll find the connection clipped to the body somewhere near the horn. what you wanna do is.. unhook the conection and connect the leads of a multimeter tool to the aux fan.

Use the multimeter to test two things. A WORKING fan should have electrical continuity. Also, if you switch the function of the meter to d/c volts, it should produce a small voltage if you rotate the fan with your hand.

If the number one makes the fan run then the problem is either the temp sensor itself or the a fore mentioned relay.

If number two fails to yield a positive result then you have a broken fan. Salvage a new fan from any W123 benz and switch it out. just make sure to do the same test with the multimeter before you salvage the fan.

Good Luck

The temp switch is not powered through a relay.

That isn't the only possibility.

How about simply unplugging the Aux fan and feeding it 12v from the battery...its eithe rgoing to work or not.

If it doesn't want to spin easily by hand...its likely not to do it under power either.

If it runs like that...then its something else and you have less to look for.

Where does the aux fan plug in?

See post #6.

I did an aux fan on my 83 in about the 2002 timeframe. This means there is TONS of info on this board with how to check it.

Id do some searching.

Did you check the fuse first?

Phillytwotank did a good writeup in #6.....I said check the fan first because its the easiest, quickest thing to check....and as a tech you learn to check the quick and easy first before spending time on the time consuming ones.