An engine start sense relay located in the M324 air conditioning accessory unit for the left
engine and in the M1455 air conditioning accessory unit for the right engine is energized when
the respective engine start switch is positioned to GRD. This relay sends a closing signal to the
latching solenoid on the bleed air regulator. This eliminates the control pressure to the PRSOV
pneumatic actuator and ensures the valve remains closed during starting.