2003 525i - Aux Fan not working with AC, but does with Temp increases

[Buster08]

I have a 525i, I had the AC on stuck in traffic and it started to overheat. I shut the AC and temp when back to normal. The Aux Fan comes on when the car starts to over heat (high speed), but not when the AC is on or low speed. I read on some of the blogs it could be a fuse, a sensor, relay or fan. I had the sensor on the bottom coolant hose a couple of years ago. I read that it could be the relay, but could not find details on the parts, location, etc. I also read that the AC should shut off if the Aux Fan is not working, but mine stays on. thoughts?

Thanks

[edjack]

The engine computer controls the aux fan, based on the rad outlet temp.

[Buster08]

Thanks The fan comes on when the engine gets too hot, but not not with the AC. I'm trying to find out is there is a different sensor or relay the controls the AC and low fan speed?. I keep reading about the relay, but can find the part or part number.

[edjack]

The fan is controlled by the engine computer. Re-read my post.

The aux fan system is tested upon engine startup: the fan should briefly spin.

[Buster08]

Thanks, is there anyway to test to see if the engine computer is malfunctioning? I do have a local garage were I have it serviced, but concerned that are not BMW savvy enough on something like this. Look like I would need to get a used one

[geargrinder]

Yes although the DME gets told that the AC is on which is how it replicates the prefacelift hardwired functionality of Aux to AC linkage (aka via the DME).

Op does your outside temp sensor work and is reading correct? AC / Aux fan behavior also is depending on that to work...

- - - Updated - - -

DMEs are almost never bad. Unless you have visible water intrusion and corrosion, they are extremely bulletproof. 99% of claims otherwise (ie “shop couldn’t find anything wrong said it must be the ECU”) are complete and utter BS. I’ve cloned a few DMEs at owner insistence in fact, telling them “the old one is almost definitely fine”only for them to find out the hard way.

[JimLev]

To add to the above.
If the fan runs at all the fuse is good.
There is no relay for the aux fan on your car.
You could be low on R134a.

[Buster08]

The outside temp seems accurate and working fine and I have over 200k on it and it still drives and runs great. Just want to rule everything out first and don't want to put in a new fan or ECU on a chance its the problem

My weekend project will be going through the fuses and checking the wiring and connector. I've done a lot of work on it over the past few years on the suspension, water pump, new radiator, alt, and hoses, etc. and maybe the Aux Wire got damaged in the process and now shorting out. Thanks

[Buster08]

I figure the fuses are good, but hate not double checking

The fan does run on high when temp is up although it was delayed coming on yesterday. I went from highway speeds for over an hour than was right in to a major traffic jam. The temp shot up really fast so I shut the air off and it took a couple of minutes for the fan to kick in and when it did it was came on very high and brought the temp back to normal, but it was close to the red. It might be that the fan is starting to go, we'll see I may replace the temp sensor again just in case Thanks

[geargrinder]

Check the temp sensor on the radiator exit for sure. Since it seems to run for overheat scenarios, perhaps it’s the AC to DME communication or wire... again don’t remember how that works whether it’s a dedicated wire, or a comma bus thing.

[Buster08]

The issues seem random and I wonder if it is a connection problem. need to get a multimeter, or better yet someone other than me that knows how to use it

[JimLev]

It's 2 dedicated wires from the temp sensor in the lower hose to the DME.
Buster, check the pressure switch connector on top of the receiver/dryer behind the pass side headlight.

[Buster08]

Thanks

[1823alex]

You may need a new climate control unit.

I've got an '03 525i as well and just went through fixing thew A/C system over the past 2 years.

First you should make sure your AC compressor is working, you will want to give it direct 12v power while the car is running and see if the compressor's clutch engages or not. Search a YouTube video for a better explanation.

If the compressor clutch DOES engage when you give it direct power then you've got a few other things to look at:

1. Does your aux fan work / briefly spin on start up of car? Does the aux fan come on for high engine temps?

2. If yes to any of those then you can rule out the aux fan, next is the system low on R134a? I'm not completely positive but I've been told before that low R134a will cause the system to not run.

3. If you're low on R134a then recharge it, and check if it works

4. If the A/C is still not working, try a new climate control unit, the stock one that came with my car did not work for whatever reason so I went to a guy in Wisconsin to buy one and it's worked great ever since.

EDIT: Looking back at some of my old posted A/C threads my '03 now has a climate unit from a 1998 which seemed to fix my issue.

https://www.bimmerforums.com/forum/s...ps-Blowing-Out

https://www.bimmerforums.com/forum/s...t-Cool-Anymore

https://www.bimmerforums.com/forum/s...s-it-should-be

Although I didn't get much help besides to take it to a profession in my threads lol.

Good luck!

[itsbrokeagain]

I was going to ask since everyone else overlooked it,but how's the clutch fan in your car? I've never had mine overheat with the aux fan not working, usually the AC pressures would rise too high and shut down before it ever got a chance to get hot.

[Buster08]

UPDATE: I cleaned all the connections, charged the A/C, and changed the temp sensor. The Aux fan is coming on with the A/C. I will keep my fingers crossed but so far so good

[computiNATEor]

Two things come to mind from my experience.
When the AC is low or out of charge, the aux fan is rarely, if ever, activated.

And as the aux fan ages, it is possible for the motor to “stick”. When I drove on a cool night at highway speeds for a long time, then got stuck in slow traffic, the temp gauge skyrocketed because the mechanical fan wasn’t yet hot enough, the thermostat couldn’t open fast enough, and the auxiliary fan was stuck. I nudged one of the aux fan blades with a stick, and it immediately started spinning again. It wasn’t like the normal DME slow start speed ramp up, either; it went straight to max speed (like a fan on a relay). I replaced that aux fan, and never had the issue again.