I posted this in the "pool cleaner" section under an old old thread but it may not get the attention it deserves.
This is a recent problem, everything was working great, no major changes made to the system.
Currently, I can have my jandy set almost all the way (full) on the VAC setting and I have normal 8PSI on pressure gauge, full strainer of water/no air bubbles but then I turn it counter clockwise another inch or so and I have air in my strainer housing, the pump starts pulsating rapidly like a jackhammer and my pressure drops to 2PSI.
Impeller spins freely when checking after pump is off, no feel of debris in there, air bled out top of filter housing. Navigator cleaner still scoots along the bottom at a decent rate. Not sure what the issue could be as this is a new home, new pool to me, the house was not maintained very well..
Other info - hayward cartridge filter, 1hp pump, hayward navigation vacuum, also located in Phoenix, AZ as some of the other threads I have read with this similar situation, coincidence?