specifically the AT-11-399 and AT-21-403 series

It will trip when pressure reaches 590 PSI and will automatically close the circuit once the system pressure drops back down to 418 PSI

While sized at 1/2"

check the ignitor resistance (ohms)

Sterling 11J11R06778-002 Pressure Switch Els PW 17895 specifically the AT-11-399 and AT-21-403The Sterling 11J11R06778 002 Pressure Switch is a critical safety and operational component designed for high performance HVAC system pressure monitoring. This OEM replacement part, which is technically identical to model J11R06778 002, ensures that your furnace or air handler operates within precise atmospheric parameters. Built to withstand the rigorous demands of industrial and commercial heating applications, this switch facilitates accurate