At the Air-Relay, disconnect the push-to-connect tubing and check the trigger circuit (from the blast control handle).
With the blast control switch activated, confrim that there is air flowing from the disconnected tube.
The air flow should be at supply air pressure but the air volume is reduced due to the size of the fittings and tubing. If you do not get supply air pressure, check the blast control switch for proper operation, and check the blast control hoses to make sure they are not kinked or internally blocked.
Check the in-line filter at the industrial interchange nipple connection on the side of the panel (where you attach the blast control hose).
If the previous steps do not fix the issue, replace the air relay.