Reverse the order of testing:

Connect the air proving switch and verify voltage at pins 1 & 4.

Connect the transformer and verify 24VAC out when energized and the air proving switch is cold.

With everything connected, powered up the unit and watched the indicator come on and go off. I turned on the fan to the air unit and the indicator came back on and very carefully bringing the voltage probe near the HV lines, I got some nice chirping.