Auxiliary (a/c) fan mayhem!!...please help

[1999750il]

Hi all,

After replacing what I believed to be a bad auxiliary fan.....I'm questioning whether the new BMW aux fan I installed is working properly.
Here is how it started.
I noticed that the original aux fan would sometimes ATTEMPT to turn but failed to even make 1 spin regardless of whether the A/C was turned on or not.
I installed a new unit ($515 from stealer) and now I do see that the DME sometimes kicks it on when I turn on the A/C but it seems to stay on for only a few minutes and then goes off.
I also scanned the car with my Launch X431 scanner and it seems to bring up a fault for Auxiliary fan...which is odd since its brand new and I have seen it spin but not with every activation of the A/C and I'm not certain if this is an issue or not. As for the A/C.....I have no issues...I recently replaced the drier and evacuated and replenished the R134....I just want to make sure that the Aux fan is coming on as needed so I don't over pressurize the compressors on HOT days while in traffic.

I've done some research and it seems that the aux fan on some e38 models behave differently than later versions...my build date is Nov 1998 and I believe my fan is controlled by the DME and not a set of 3 relays..therefore my fan will not come on for 30 seconds with every start of the engine and it may only come on under the correct conditions.

Can anyone help me figure out a way to verify that the aux fan is being controlled properly by the DME? As I stated...the air comes out cold and with my scan tool I can verify that the pressure signal to the DME is above 11 bar at idle with the A/C on and it climbs from there. I believe my model year needs to have the proper signal from the A/C high pressure valve before it will get turned on as well.
The car was at operating temp and while it would SOMETIMES command the aux fan on....I could not get it to do it consistently.

Any advice would be deeply appreciated

Thanks
Rick

[racer2086]

I'm on my phone, so can't verify on my computer, but believe you are dealing with a PWM controlled aux fan. So the thing will only run when it needs to and will be speed dependent based on the DME signal.

What's your ambient temperature?

[1999750il]

Thanks Racer

I appreciate the quick reply. Its about 70 degrees here in NY and I had the car running for half an hour to see if that would help.
The fan is PWM controlled. I just cant understand under hat conditions is should come on and go off. It certainly does not come in for 30 seconds with every engine start....but I believe that only the earlier e38 do that.
The other weird issue is that I cant command it on with my Launch x431 scanner...but I'm not sure if its set up to do that

Again...I appreciate your quick reply

[Bigrobsbmw]

Have you changed out the temperature sensor in the bottom radiator hose ? That must be operable for the fan to turn on. I'm pretty sure.

[1999750il]

Hi bigrob,

Yes I have also replaced the temp switch on the lower radiator hose but I believe that switch will only turn on the fans once the engine coolant is close to over heating. I don't believe that switch has any control over the aux fan for a/c purposes. I'm not even sure if there is a problem with the new aux fan but I just wish there was a consistent way I can test to verify that its coming on or at least being commanded to come on under the right circumstances.

Thanks for your help

[Mayorchuck]

I don't have any personal experience with the Electric fan but here is the info from the WDS.


Electric Fan

Vehicles with M62TU, S62 and M73 engines feature a viscous fan as well as an electric fan. The electric fan cuts in when the cooling capacity of the viscous fan is no longer sufficient.
The electric fan is activated by means of a power output stage directly on the fan motor. The motor control unit activates this power output stage by means of a square-wave signal with duty factors (variable pulse width) between 10 % and 90 % thus controlling the various speeds of the electric fan. Pulse duty factors less than 5 % and greater than 95 % do not trigger activation but rather they are used for fault detection purposes. The power output stage features its own positive and ground supply.
The fan speed is influenced by the coolant temperature at the radiator outlet and the pressure in the air conditioning system. The fan speed is reduced as the vehicle speed increases.
If a fault occurs during operation a corresponding fault code will be stored in the fault code memory of the DME control unit.
For the purpose of checking operation and troubleshooting, the diagnostic program offers the option of activating the electric fan directly via the DIS tester/MoDiC.

[1999750il]

Hi Mayor,

Thanks for the info. It was informative. Its almost impossible to find at what coolant temperature and a/c pressure value will start the aux fan spinning.

[Mayorchuck]

Specified values, pressure sensor

Data on working range and substitute values.
The pressure sensor receives a 5 volt power supply from the control unit for the heating/air-conditioning system. The sensor signal is evaluated with the help of tables and forwarded to the engine electronic via the K bus. In the process, the refrigerant pressure in the air-conditioning circuit is converted to a load torque and the required fan stage.
Refrigerant pressure-fan stage conversion table
Each fan stage that is determined is transmitted via a telegram from the engine electronics. Prerequisite is a speed less than 80 km/h.

Pressure in bar	Fan stage
8
9	1
11	2
13	3
14	4
15	5
16	6
17	7
18	8
19	9
20	10
21	11
22	12
23	13
24	14
> 24	15

- - - Updated - - -

Dug around a bit more to find the above table. Anything else on the system is related to the 2 stage aux fan on the pre E38's.

[racer2086]

You know, I have not done a lot of diagnostics on the facelift PWM system, so I'm kinda just thinking out loud here...

I know through INPA you can read the pressure. Your ambient temp being at 70 is low and may be low enough that the viscous fan is keeping the condenser cool enough and pressure down for the Aux fan to not trigger much. I do not know, but assume, that the car takes the outside ambient temperature into account also when running the Aux fan. With 70 degrees outside, it may know that the viscous fan can keep up. Your outside temp in the cluster is reading properly, correct? When the sensor dies, it defaults to -40 degrees.

In FL here, my outside temp reads 100-108*F in the summer months here. My pre-facelift fan runs on what I think is the medium speed. I rarely hear it go up to the highest speed. I do have a recalibrated t-stat that keeps engine temps around 100*C. Anyway, an ambient of 70 degrees is pretty cool as it is, so I wouldn't be terribly concerned the fan isn't running much. Hopefully you can try it out on a hot day and see what it does.

Edit: the compressor also has a mechanical blow off valve that will vent the system if it gets too high, but we're talking like 400 psi. Also, I think the DME will cut the compressor clutch if it gets too high.

[1999750il]

hi racer,

That is certainly good advice. I thought that the 70 to 75 degree temp may not had been hot enough to engage the fan more steadily. The outside temp sensor, viscous clutch are both new and should be working fine.
I knew about the blow off valve at the compressor once it reaches too high of a pressure and just wanted to prevent that scenario by making sure the aux fan would kick in when needed.
I recently evacuated the ac system, replaced the drier/receiver and recharged it...so I wanted to make sure the entire system would remain in tip-top shape.
I guess I was just being overly worried with aux fan and should wait for a hot enough day to se how it behaves.

Thanks for the advice