This is what is written in the manual for the a/c recovery/recharge unit:

"In some instances a differential condition may occur. This happens when there is a pressure balance between the unit and the vehicle air conditioning system. If a differential condition is reached, the PRESSURIZING TANK light will begin flashing. To correct a differential condition, turn the engine on, start the vehicle air conditioning system and press START/STOP OPERATION on the left hand panel."

Well, I've done that and it still does not draw refrigerant into the system. I jumped the pressure switch to get the compressor to turn on and the clutch spins freely while it's on. It's not intermittent.

I really need to know how to get that pressure gradient taken care of. Do I need to evacuate the system and draw a vacuum again now that I have the compressor running?