My 2004 mcs blows regular air when activated. A few days ago when the ac worked, I would hear a roaring sound at high rpm when the ac was on.

When I try to turn on the ac, I hear no noise difference in the idle that indicates that the ac turned on.

 

It may be low on refrigerant. You can try installing a can but I would bring it to someone with the know how and equipment to do it right.

///Rich

 

I read somewhere that if it was low on refrigerant, the ac light would blink but it doesn't for me.

 

I've had very good luck with AC Pro.