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  #11  
Old 07-08-2015, 11:14 AM
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Ac control is the unit with the buttons. You need to remove the trim and a few bolts to pull it out. High pressure could be suspect for the fan running at high speed, but you have this communication code. You have to read the actual values from the AC control.
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  #12  
Old 07-08-2015, 01:01 PM
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more on possible causes for aux fan to run high all the time when AC is ON.

"...the electric cooling fan is controlled by the ECM via the output final stage. The output final stage is mounted on the fan housing, next to the fan motor. The fan is operated using a pulse width modulated signal. Fan circuit wiring is protected by a 50 amp fuse. Electric fan activation is based on the following inputs to the ECM:


  • Radiator outlet temperature
  • Calculated catalytic converter temperature
  • Vehicle Speed
  • Battery voltage
  • Calculated A/C pressure

When the vehicle is first started, the ECM activates the fan briefly at 20% of its maximum speed, then switched off. This is for diagnostic monitoring. The voltage generated by the fan when it slows down (acting as a generator) must match the stored rpm values in the fan output stage to confirm that the fan is operating correctly.

There is a control module mounted to the aux fan housing that receives a variable signal from the DME, which then controls fan speed. It may be bad. The PWM speed control is inside the fan motor housing, it's speed is continuously variable from the duty cycle of pulses it receives from the DME.

So its either the PWM on the Fan housing is bad or DME is sending signal to PWM to run high seeing AC pressure is High.

AC has 2 pressure input Low and high, low is used to put the gas. I also see a sensor on the high side (small pipe).


Last edited by freshwater; 07-08-2015 at 03:13 PM.
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  #13  
Old 07-08-2015, 03:11 PM
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Did a small test to verify the freon Gas. Put the gauge on low pressure side, outside temp was 70F, I got ~30psi within the Green range of 25psi to 45psi.
I dont have the Full AC gauge system to hook up the high pressure side to create a full loop, I have seen that selling in walmart.
Today I am observing that my fan is running but not that loud or high but that could change any minute as I have seen in the past.
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Last edited by freshwater; 07-08-2015 at 03:17 PM.
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  #14  
Old 07-08-2015, 03:29 PM
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You can just read the actual values in the AC control module and see what the pressures are and how many % fan speed is requested by the AC module.
Normally when the fan control unit goes bad the fan does not work at all. Most of the time, if the fan runs on highest speed all the time this is some kind of safe mode caused by a parameter going out of limits.
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  #15  
Old 07-08-2015, 03:41 PM
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^^And how to read the actual values from the AC control. Do I need to hook up something or they are visible on AC control. I still couldn't figure out how to remove the trim on the AC panel in the Car where all the AC buttons are in the middle.

Thanks for your support @bawareca
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  #16  
Old 07-08-2015, 04:06 PM
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Refrigerant Circuit Pressure Sensor

The refrigerant pressure input signal is a direct junction box input signal and is relayed to
the IHKA via the K-CAN. The IHKA requests actuation of the auxiliary blower by the DME
(ECM) depending on the refrigerant pressure.
The IHKA determines the relevant A/C compressor load torque on the basis of the input
signals from the pressure sensor and the compressor speed. The DME (ECM) control
units are notified of the load torques by the IHKA and used by the DME (ECM) as input
variables for actuating the electric fan

Is this could be the Culprit as shown in Red circle.
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  #17  
Old 07-08-2015, 06:06 PM
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Again, you have to read the actual values to find the culprit.
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  #18  
Old 07-27-2015, 03:13 AM
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I like to update and seems like My Aux Fan problem of running very loud when AC is turned ON is fixed.

After replacing the A/C pressure sensor on the High pressure line I don't hear the Aux Fan going crazy. The Compressor is still engaging and Car is Cooling fine but no more Fan sound.
I need to Vacuum the R134a at local shop before I remove the Sensor, I used 15/16" Wrench and it was quiet tight before it get loose. After putting back the new sensor I add ~12oz of R134a and bring to 28psi at 80F and it start cooling again. I believe E70 takes 1.1lb +- of R134a on a complete empty system.
Never over fill the R134a it can cause problems. I will check it out with local shop how much more I need.


See the 2 pics of the part I replaced $35 and the location of the part on my E70 N62.


Mfg Part # 64539181464
A/C pressure sensor located in A/C line from receiver-drier to evaporator.
This sensor attaches to the a/c line and detects the amount of line pressure for the a/c compressor to engage. Works in conjunction with the climate control system and the air conditioner.
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