The gun trigger is active, but no A pulses (QTA1, QTA2, QTA3) or no B pulses (QTB1) are detected during the dose time selected.
Fully trigger the gun.
Increase flow rate.
See Ratio Low Error and Ratio High Error, R1 and R4.
Turn on the supply pump.
Check the air lines for leaks and repair.
Clean or replace air flow switch.