Air Cond Low Gas affected Aux Fan?

[bimmerholic]

how about AUX FAN at high speed all the time even during cold start and idling. Anyone face this problem

It could be your resistor pack that's faulty. It can't find low speed so it's running on full speed all the time. Check the resistor pack on the AUX fan bracket.

 

[jarance]

Guys, sorry for misinformation. Our ride does not come with pressure switch. It comes with pressure sensor. If it pressure switch, it will have 2 wires. The pressure sensor comes with 3 wires.

So please do not short the connector.

Will post correct info later.

OK borrow picture from everybody (sorry !)

The pressure switch for low pressure should be located on the dryer of the aircon. see picture below

A close up picture of the pressure switch.

The function of the pressure switch is to protect the aircon compressor when there is insufficient gas.
Here is a schematic diagram of the aircon control. As you can see the pressure switch is before the compressor clutch & Aux fan so even though the snowflake light is on, the clutch will not engage if the gas pressure is LOW.

You can test the clutch by making a jumper as shown below. However, do not run it too long cos compressor will be damage due to "dry" running.

As you can see from the picture below, there are 2 circular rings on the front of the AC compressor. The outer ring is the pulley which is driven by the belt. The inner ring is the pulley which will drive the AC compressor when the magnetic clutch is engaged. So check whether the inner ring is rotating or not.

 

[jarance]

Apparently, for E46 and E39, the aux fan are variable speed. For older model like E36, there are only 2 speed which is controlled by resistor dropper and cut-in by thermostat switch.

Here is an extract from BMW WDS info.

Additional info.

 

[jarance]

The aux fan is control by the radiator temperature and a/c grass pressure.

Depending on the gas pressure, the fan will operated according to the chart below.

 

[jarance]

Furthermore, the aircon is control as follows:-

 

[jarance]

For those who are interested in the wiring schematic have a look at below:-

aircon control.

Temperature sensing.