(2)  
On airplanes:

 (a)  BEJ 061-062 POST-SB 36-1016; BEJ 101-999; An engine start sense relay for each engine is located in the M324 air conditioning accessory unit. The respective relay is energized when the engine start switch is positioned to GRD. This action energizes the closing coil of the latching solenoid in the bleed air regulator. This eliminates control pressure to the PRSOV pneumatic actuator and ensures the valve remains closed during starting.

 (3)  
On airplanes:

 (a)  BEJ 061-062 PRE-SB 36-1016; The reverse flow of the air will actuate the reverse flow switch in the bleed air regulator. Actuation of the reverse flow switch will energize the closing coil of the latching solenoid in the bleed air regulator. This will eliminate control pressure to the pneumatic actuator of the PRSOV and cause the valve to close.

 (4)  
On airplanes:

 (a)  BEJ 061-062 POST-SB 36-1016; BEJ 101-999; The engine start switch positioned to off will de-energize the respective engine start sense relay in the M324 air conditioning accessory unit. This will de-energize the latching solenoid on the bleed air regulator allowing control pressure to the pneumatic actuator in the PRSOV.

 (5)  
On airplanes:

 (a)  BEJ 061-062 PRE-SB 36-1016; The upstream pressure will exceed the downstream pressure after the engine has started. This change in differential pressure sensed at the reverse flow switch opens the the reverse flow switch. This in turn de-energizes the latching solenoid of the bleed air regulator allowing control pressure to the pneumatic actuator in the PRSOV.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

CONDITION: BLEED SWITCH "OFF" - FIRE SWITCH "NORMAL"

737-400 AIRPLANES: M1455 RIGHT AIR COND ACCESS UNIT (E3-2)
Bleed Air Control Circuit (Example)
Figure 10

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
CLOSE COIL
OPEN BUS 2 28V DC COIL
28V DC BAT BUS

BLEED AIR OVERHEAT SWITCH
CONDITION: STARTING ENGINE - BLEED SWITCHES "ON" - FIRE SITUATION "NORMAL"
Bleed Air Control Circuit (Engine Starting)
Figure 11 (Sheet 1)

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 BEJ 061-062 POST-SB 36-1016; ú 36-11-05
 BEJ 101-999  ú
 ú 09 ú BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.  Page 24Mar 12/02 

A 737-300/400/500MAINTENANCE MANUAL

BLEED AIR OVERHEAT SWITCH
CONDITION: STARTING ENGINE - BLEED SWITCHES "ON" - FIRE SITUATION "NORMAL"
Bleed Air Control Circuit (Engine Starting)
Figure 11 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
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 WITH REVERSE FLOW SWITCH ASSEMBLY  ú ú 03 Page 26 ú Nov 12/01
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BLEED AIR REGULATOR(REMOTELY MOUNTED)
　
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