That's really helpful too @Ken W - thanks. I would imagine too if the fan is at full blast yes it would be very loud inside - right now you can't even hear the airflow in mine! At the end of the day it's not killing me yet because the interior does eventually cool down with the partial airflow, just not right away. But your suggestion to bypass the speed controller is a good process of elimination - I just need to properly lie on my back with my legs over the passenger seat and when the weather fines up I'll have a go ...If you take the wiring connector out of the speed controller (located just under the heater pipes), that will give you access to the motor wires. There are two clips either side that need to be held against the conncetor block to get the connector to release. If you turn on the ignition you will find the ?red wire at one end of the connector has 12 volts and the black wire at the other end is grounded to chassis. The motor will run at full speed if you connected second ?red wire beside the 12 volt wire to the ground wire. Expect a big spark if you link those up with the ignition on.
Is the motor speed greater than you get through the aircon speed control? If so you may have dodgy fan speed controller.
On our C5X7, if you push the auto button, the fan noise is so loud, it is difficult to talk to other people in the car.
Cheers, Ken