What cause A/C compressor not engage?

[upallnight]

Originally Posted by E53inLA

We had a bad Aux Fan in our 2005 E53. Now I know, if I turn on the AC full blast and the Aux Fan doesn't come on with 30-60 seconds, something is wrong.

The funny thing is I remember when the X5 was new the Aux fan would run for a while after we turned off the engine. When it failed, I just didn't notice that any more. Mechanic told me it's not a well made part and is prone to failure.

It's not that it not a well made part, but a complicated part. Before it was just a DC motor that was switch on and off with a relay, but now the aux fan is controlled by the DME which sends a pulse signal to the circuit board that is built into the motor that interprets the pulse to turn it on and the width of the pulse to determine the speed of the aux fan. The more you make something complicated the more the chances of failure.

[E53inLA]

Originally Posted by upallnight

It's not that it not a well made part, but a complicated part. Before it was just a DC motor that was switch on and off with a relay, but now the aux fan is controlled by the DME which sends a pulse signal to the circuit board that is built into the motor that interprets the pulse to turn it on and the width of the pulse to determine the speed of the aux fan. The more you make something complicated the more the chances of failure.

No argument there. In our case, the AC would not work in city (stop & go) traffic, but would work at constant highway speed.

After the fan was replaced, if I start the motor, turned the AC on max, the fan would start within 30-60 seconds, and the AC would blow cold. This is standing in my driveway.