I have exactly the same problem on my wma32
I've replaced the pressure switch and tube and it still does it
I've also removed the pressure shamber and tried the old bicycle inner tube test of dunking it in a bucket of water to see if I can see any bubbles - still no joy.
Try disconnecting the clear tube that runs from the pressure chamber under the drum to the switch above the drum - start the cycle and blow gentily down the tube the drum should start spining - if it doesn't then it's the switch ... if it does start spinning then you're in the same boat as me
pac st
May 2007