[musicrocker]

I have a UK BMW F10 (520D 2011)

Before this problem started, if I put the demister on full speed it always stayed on full speed and I was able to control the fan speed manually.

Since last few days, the Fan doesn't come on full speed even if I put it to maximum which was working before.
When the problem first started, I put the demister on full speed to clear the front windscreen and it would work on full speed for a minute or so and then go back to very low speed even if the fan setting is set to the highest speed. It will intermittently come back to full speed and then go back to minimal again. Now a days even if I put the demister on with fan speed set to maximum it only blows air very slowly like it does if the setting is on one bar.

When I started the car today and put it on Auto mode the fan went off to maximum and then went down to minimum. In manual mode even if I set the fan speed to max it does't work on full speed rather on a very reduced speed.

Would you be able to give me any clue as to what might be the problem?
If it is the final resistor unit which needs replacing, is there a video which I can follow and where to buy the parts?

Thanks
pradeep

[JCMech]

Might be a weak battery. Do you know how old is it?
Try charging the battery fully, start the car and retest.

[Stück]

Indeed, I've seen many F chassis cars come through the shop with marginal batteries and the car is limiting current draw to the blower to maintain charge in the battery.

Have the battery tested before you do anything else.