Disengage the blast control switch. Adjust the pump inlet air pressure regulator until the pump air pressure regulator gauge reads 100 psi (6.9 Bar, 0.69 MPa).
If you are unable to attain this setting, check the air inlet filters and make sure the supply air pressure is greater than or equal to 100 psi.
If the above steps do not resolve the issue, replace the pump air pressure regulator.