As a sanity check for the procedure I gave above I called and had a chat with my Garmin Tech person, Robert Archer. He told me my procedure was almost correct except I should not be using the steering wheel to place the rudder hard over. This engages the shadow drive which opens the check valves and inhibits the Auto Pilot stall condition.
Instead, the correct procedure, unless you disable the shadow drive, is to use the Auto Pilot's left or right arrows to change heading. Hold one of the arrow keys down or continuously press and release until the rudder is hard over. When the rudder is hard over the 'stall' message should display and the pump noise should at same time stop making its noise. If this 'stall' message is not displayed and the pump continues to make a noise then there's air in the line.
I will test this new procedure and post back my results.