First of all i would pipe inlet to the pressure switch and check for blockage on the switch and it’s supplying pipe. Some times the diaphram in the switch rips rendering the switch useless or unrliablt. Pressure switches are cheap or atleast the square D 30-50psi with manual on off switch bar are cheap 12.50 to 35.00. Next if it is a newer diphram tank it is supose to have pressure even when empty. If the switch don’t fix you I would contact a local plumber experianced in wells or an irragation supplier. all so determine what is the top pressure you would like to run your system (don’t exceed 60) and set your switch &tank air pressure according whomever helps you’s instructions.