A/C & Auxiliary Fan Diagnosis Verification Please!

[masbury]

The car: 1997 528i - 05/29/96

The problem: Auxiliary fan does not turn on when A/C is engaged.

Replaced auxiliary fan due to broken blades and non-op of original with Hella/Behr. Replaced two stage temperature switch with BMW.

When engaging A/C, compressor clutch engages and A/C blows cold air, however auxiliary fan does not operate.

Fuses checked good. Have not checked relays.

Questions:
Does the engine have to be at normal operating temp for the auxiliary fan to kick on with the A/C?
Does the external air temp sensor have any effect on auxiliary fan operation?
Can anyone shed some light on the external air temp sensor installation location? I found it hanging under the car and since having the whole front end off, I cannot locate a bung or hole or anything that it fits into. On my 850, it fits into one of the brake ducts (if I remember correctly). Can't find anywhere for it to fit in.
Could I have a bad control unit in the dash? It does act a bit squirrely. When engaging the A/C, if the fan speed is on low, it will increase it to 1/2 way up.

I'm kind of running out of ideas. All help and suggestions would be greatly appreciated.

Thank you,

Mike

[JimLev]

Your 97 should have resistors in the fan circuit for low and medium speed control. They are know to burn out so the fan won't operate on those two speeds. The resistors are mounted on the aux fan frame.
Your temp sensor under the bumper has nothing to do with the Aux fan not working.

[edjack]

If the temp on the cluster reads -40 deg, the side mirrors will eventually cook and become opaque.

The ext temp sensor fits into the bottom of the plastic finisher at the lower right side of the front bumper. Sounds like yours is missing, not uncommon, esp when striking curbs and such.

This video is for the E46. The E39 sensor is mounted to the right side. Otherwise, the procedure is similar

https://www.youtube.com/watch?v=RrgeWWZ4dnk

This link shows how to cobber up a different mounting:

http://bimmerboard.com/forums/posts/181335/

This is a reason to replace the sensor.

https://www.bimmerforums.com/forum/s...erature-Sensor

Here is the resistor assembly noted by Jim, item 8: https://www.realoem.com/bmw/enUS/sho...diagId=64_0832

[masbury]

Gentlemen, thank you for the prompt response.

I probably failed to mention that the new auxiliary fan came with all new resistors as well, so short version - fan, resistors and fan 2 stage temp switch are all new. Fuses checked - all good.

The A/C does operate normally, however the auxiliary fan does not operate at all.

I must be missing something, but for the life of me, I don't know what.

[edjack]

The relay(s) may have failed.

There are three, but the suspicious one is K21, which controls the normal speed. It's in the E-box, the one closest to the right side of the E-box.

[TooEasyL2P]

Have you checked fuse near battery?

There's 100A fuse (or 110????) in the back near battery. It's in that white box where you need to remove cover to see fuses.

I had same problem and couldn't figure it out, because that fuse isn't called fan fuse or something like that. It's called "fuse for fuse box number something". It's a fuse for those 2 fuses under the glove box.

Well at least it's like that on my 530d. Maybe it's like that on diesel engines. In my case glow plug relay and fan wasn't working.

[masbury]

Checked the fuse in the box in trunk by the battery. All are good (tested with meter). So I guess it's relay time.

I'll update after that.

Thanks again,

Mike

[masbury]

Update;

I, apparently am too clueless to work on these things. I finally discovered fuse 7 was missing. Put a fuse in, have 12v to 30 & 87 in the relay socket. Plugged the relay back in, started the engine, hit the a/c button - blew 7.

Is there a somewhat common place for a short (I'm assuming a short)?

Electrical is not my strongest suit.

Thank you

[edjack]

Is this a new relay? If so, sounds like there is a wiring fault.

[masbury]

Yes, I did install a new relay, so I guess I have to try and find a short or whatever is causing fuse 7 to blow.

Is there a possibility the HVAC control is causing this problem. It's a little hinky in that when I change the temp, the fan speed increases whether I change the temp up or down. It's weird.

Thanks for all your help,

Mike

[JimLev]

F7 (20A) feed power thru the relay (K21) contacts and then to one end of the resistor on the fan frame for the low speed.
Pull the relay and see if the fuse still blows, that will tell you which side of the relay the short is on.

[masbury]

Jim;

Did as you suggested. Fuse 7 did not blow. Does this mean the short is on the load side of the relay?

Thanks,

Mike

[JimLev]

Jim;

Did as you suggested. Fuse 7 did not blow. Does this mean the short is on the load side of the relay?

Thanks,

Mike

Yes, either the wire from the relay to the fan frame is pinched or it could be shorted to the chassis where the wire connects to the resistor.

[masbury]

Thanks, Jim. At least I have a starting point. If you think too long about how much wiring there is in these cars, you get somewhat overwhelmed.

Appreciate it,

Mike