At the end of 20 seconds, a power relay turns on the actual compressor motor.

Hi Michel,

My brother will get a charge out of what you wrote, about the rotating beacon and seatbelt chime.

Twenty five years ago, when he started his cabinetmaking business in his garage, he complained to me about the automatic pressure switch starting the compressor and stopping his heart. I made a similar delay device with a squeaky buzzer to warn him; he thanks me every year for that.
--
Art Benstein near Baltimore