How do I know that he turbo is working or when does it kick in?
2007 s60 2.5T

 

Two ways listen for a whine or woosh sound when you Rev the engine.Or do what a lot of us did and put in a Boost gauge.The turbo kicks in at 2500rpm or so for a Auto and its only really gets used when you give it a lot of gas all at one time driving 30-40mph then stomp it.If the car takes off its fine.

 

As MYS6T said, you'll know if it is working if you accelerate hard and all of a sudden the car seems to leap forward when the turbo kicks in. But the turbo whine is another give away. Drive with the radio off and the AC off and listen for it.

 

i am very frustrated with this as well. even totally quiet it is very difficult to hear. i have heard that putting in a cone filter and ditching to stock airbox helps this. can anyone confirm or deny this?

 

If you remove the top of your airbox and put a cone filter on the end of your MAF you should hear the engine sucking in air when you press the gas pedal.

Also when you let off the gas you should hear a Whoosh kind of like a BOV. That is your CBV venting the air back into the system.

I have a short ram intake on my 1999 S70 AWD and it uses a cone filter. I hear it everyday I drive me car.

Here is a good article on how turbos work.
http://auto.howstuffworks.com/turbo.htm

With all that said if you gun it your car should take off at a nice clip. If it doesn't then either your turbo is bad and or your car isn't turboed.