start at the top
while u plan to dismantle the intake plumbing under the windscreen, do the following before u start:
- remove F7 and observe. Noise gone, probably a stuck blower motor. It can be other devices using F7 as well so it's not clear cut just yet.
- before removing the blower motor, but with most of the casing removed, insert F7 and switch the blower motor on. The buzzing should be more louder now if it's the motor. You might even see the motor attemting to spin or spin slowly ...
- try to 'jump start' the motor by spinning it by hand, first without power applied (it should turn freely - any binding points to worn bearings / bushes) and then with power applied (watch out !! those little plastic blades are just that - blades!).
- try some lubrication of the motor after removing it from the housing - the fan should spin freely.
- measure the voltage across the motor with F7 in and the fan switched on - should be close to battery voltage. Seeing F7 is OK the current should be within spec. A low voltage points to a faulty relay / resistor pack.
any binding shows to a shot motor. If the motor is OK, the relay driving it might be shot, or it's the controller unit.
This is where I run out of ideas ...