I had the alternator for 01' A6 replaced by a dealer recently. Then the blower fuse (#25) is repeatedly blown. Before the repair, it was perfectly fine. Any idea or suggestion would be appreciated.

 

Does the fuse have the proper rating (in Amps)? Maybe the PO replaced it with what was available at the time and never corrected the issue.
Perhaps your new alternator produces more juice so the under-sized fuse blows up.
The other possibility is that you now have a short in the blower motor.

 

Thanks for your kind response. The fuse (#25) rate is the same: 30AMP. Sometimes a fuse can last for hours, but for most time, it is immediately blown once fan is turned on when engine is running. Without engine running, it is fine. Where and what should I check for the shortage?
The replacement of alternator was done by Audi certified techs in a Audi dealership (Vision Audi). I was told it is a new alternator. I assumed that they would do a good job.

 

You could check for a short using an ohm-meter. From negative to positive there should be no resistance. Then from either negative or positive to ground (car chassis is a good example) there should be infinite resistance other wise the motor is shorted and you found your culprit.

 

You should check the output voltage of the alternator. With the car NOT running, check the voltage across the battery terminals. SHould be around 12.8 volts. Now, start the car and repeat the test. SHould be aroung 13.8 volts. Anything higher and the internal voltage regulator in the alternator is not working correctly.

If these check out, then it is the blower motor, not the alternator. If the old alternator did not put out a full 13.8 volts, then the blower motor might have been just below the amperage threshold of the fuse. With a new, more enthusiastic alternator, you could be just above the threshold of the fuse. In this case, a new blower motor and/or resistor pack will solve your problems.

Bob

 

Bob,
Thanks. You are right that the output of alternator is 14.2 V, which is higher than 13.8 V when engine is running. I'll post the feedback after I talk to the dealer who did the repair next week.