A/C recharge questions

[Vladimir Entin <ventin@hns.com>]

What is the procedure to charge an air condition on Audi 5000CS ?
On other cars it is charged through the low pressure end with engine
running and compressor clutch "ON". 
In order to do that on Audis the low pressure switch should be removed 
and low pressure switch connectors should be bridged. Then it may be 
charged through the low pressure switch valve with the climate control
on "LO". Is that the way to go?.
Why the Bentley recommends to evacuate system before recharging?
Is it possible just to add a pound of refigerant ?. Is refrigerant 
oil needs to be added while adding refrigerant?

Yuor suggestions will be greatly appreciated.

Thanks,

Vladimir