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Discussion Starter · #1 ·
First post, so hello and all that good stuff....

BMW aren't my area of expertise, but I had my AC regassed today and the guy told me that the fan at the very front of the car behind the grille wasn't coming on when the car was standing still and that this fan is what fed air into the AC and that I would need to get this looked at otherwise the AC would pack up and it would be mungo expensive.

Now to my mind this fan is just for the car's radiator, if the AC is off (or on for that matter) you can still control the amount of blow (as it were) also I don't think that fan has ever come into play as my temp has always stayed in the middle.

Is the guy (a) as unkowlegable as I am (b) jerking me about (c) telling the truth and that I need to invest some more ££££ into it.

Many thanks in advance to anyone with more knowledge than me, which would be all of you.
 

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He's right about the fan and wrong in his explanation (or you didn't understand what he said). In front of the radiator is the air conditioner condenser (looks like a thin version of the radiator). The condenser's function is to cool the R-134 refrigerant (the "gas" in the system). If the fan is not blowing air across the condenser the system pressure rises tremendously and can blow the saftey plugs and release the excess pressure (and a lot of the brand new R-134 as well!). If that fan isn't coming on as soon as you turn the compressor on, (the "snowflake" button) you shouldn't EVEN be trying to use the AC mode! If you were moving ALL the time the normal air flow through the condenser and radiator would probably suffice but I'm sure that there are plenty of stop signs and lights in Merry Old England! Get it fixed before you use the AC mode! LOL!
 

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Discussion Starter · #3 ·
Thanks very much for that, there are indeed plenty of opportunities to stop here

Anyone got any ideas as to where the fault may be, all the wires are connected and the fuses are all in tact, and outside of that I haven't got a clue where to look.

Is there a relay that runs it?

Are there some fuses that I have overlooked? (I've checked inside the glovebox and boot are there more elsewhere)

If its supposed to come on as soon as the AC button is hit can I hope that this is fairly simple (i.e. cheap) to fix, or am I being to hopeful.

Many thanks again
 

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I searched for "auxiliary fan" and here is an old post I found:

The initial test - turn on the AC. Does the fan run? No? Then in all likelyhood the fan has gone deceased.

Why? The E39 likes to suck up leaves and crap into the fan. These build up behind the fan, clogging up the guts, and eventually it doesn't run. BTDT with my '98. New fan lists for $330, takes about an hour (if you have the right tools) to install.

To test the fan itself, you'll need a source of 12VDC (I use a motorcycle battery). The connector for it is on the upper left side of the housing. Disconnect it. You'll find a bunch of female pins on the connector going to the motor. I don't have the wiring diagram handy (I traced it out), but the BIG wire is ground. Put negative to that wire. Connect positive to any of the other pins. The fan should run. It should run at a different speed for each pin. It has 3 speeds, from VERY FAST to AWFULLY FAST to FAST.

If it runs on all three speeds - the motor and resistor packs are OK (the resistors are mounted on the fan housing). Your problem is either the temperature sensor OR the fan relay. The temperature sensor screws into the back of the radiator on the reservoir side. Has a green connector going to it (from memory). IF the fan motor ran in the test above, you can jumper pins on this connector to test the relay pack. I don't have the pinouts handy (but if you post your email address I'll contact you directly).

If the fan motor works, and jumping the wiring from the temperature sensor works - then it's the temperature sensor that's bad.

If the fan motor works, and jumping the wiring from the temperature sensor doesn't work - it's either the fan relay or the fan fuse that is bad. Dunno where the fan relay is, because I never bothered looking for it once I figured out my fan motor was bad.

If the fan motor is bad - you have three choices:

1. Throw $330 to the parts guy and buy the fan and install it yourself.

2. Throw even more money to the service department and have them install it (it isn't THAT hard a job.. I did it after dark in less than an hour, and that included cleaning all the crap off the front of the AC condensor that was behind the fan shroud.)

3. Take the old fan out and try to fix it. Then reinstall it. I did fix the old fan (it's in my loft in the garage as a spare now.. I did #1). Turn the fan over, use your air-compressor to blow as much of the crap out of the inside of the motor as you can. The motor is swaged together - meaning you can't take it apart. Then spray electrical contact cleaner into the cooling holes in the back while spinning the blade. Let it dry. Connect it to a 12V source and try spinning it by hand. Mine initially didn't do much, but after lots of hand spinning, the motor started to catch intermittently. I repeated the air-blasts and contact cleaner, and connected it again. It got better. I kept blasting it out, running it, and eventually started spritzing WD40 in the holes. After a few hours of this kind of playing around - it ran just fine - on all 3 speeds. It went back into the box the new one came in and got stored away as a spare.

(Reference w/follow up post about removal procedure: http://bimmerfest.com/forums/showthread.php?t=56285&highlight=auxiliary+fan)

Here is an E38 post with some photos and instructions how to get to that resistor.

http://www.laczik.org/BMW/repair/E38_aux_fan/E38_aux_fan.html

 
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