I get the same ventilation blower sound when I turn on the ignition. Sort of a HUMMMMMM. Per Adrian's book the rear blower runs at 2V when the fan switch is at "0". I have a 90 C2 and that is the only sound I get!!!

 

hjcarlin72......right on...I double checked my system.....and hear the same....I didn't have the fan switch "0" first time...so I heard the left, right fan's in luggage compartment....set switch to "0"....now just hear vent blower.
My error....thank's, Jim

 

Now that makes sense! I always heard that hum and thought it might be the death rattle of a fuel pump - even though the car was not running.

Marc

 

To summarise possible reasons for "key on" sounds:
1. climate control servo(s) repositioning - this one is only a few seconds long
2. temp sampler fan starts running behind CCU
3. front blowers start at "minimum" speed
4. rear blower starts if temp control **** set above ambient
5. C4 only - PDAS booster pump getting up to pressure
There's a lot going on. Are there any more?

 

Darryl....that SURE sum's it UP !!!!! .......so we do have Front blower's going (which is in rear of luggage compartment). All enumerated is a 10/4.
Thank's, Jim