21 REMOVE THE PNEUMATIC
41 REMOVE THE PNEUMATIC
PRESSURE FROM THE SYSTEM PRESSURE FROM THE SYSTEM
(AMM 36-05-00/201). (AMM 36-05-00/201).

REPLACE THE DUCT PRESSURE REPLACE THE DUCT PRESSURE TRANSMITTER ON THE AFFECTEDINDICATOR ON THE P5 PANEL.SIDE (AMM 36-21-11/401).
NOTE:  MAKE SURE THE AMBIENT VENT ON THE DUCT PRES-SURE TRANSMITTER IS NOT CAPPED.
SUPPLY PNEUMATIC PRESSURE WITH THE APU OR GROUND AIRSOURCE WITH THE ISOLATION VALVE OPENED.
 DOES THE LOW DUCT PRESSURE CONDITION STILL OCCUR?
NO
42 REMOVE THE PNEUMATIC

PRESSURE FROM THE SYSTEM
(AMM 36-05-00/201).
CONTINUE THE AIRPLANE IN SERVICE.
B05523
Low Duct Pressure. The Engine Was the Bleed Source.
Figure 104 (Sheet 1)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
FROM SHEET 1 (BLOCK 1)
NO
NO

2 REMOVE THE PNEUMATIC PRES-SURE FROM THE SYSTEM
(AMM 36-05-00/201).

NOTE: VALVE THAT WILL NOT MODULATE CORRECTLY CAN CAUSE A LOW DUCT PRESSURE CONDITION.
____A PRECOOLER CONTROL
OPEN THE FAN COWL PANELS AND THRUST REVERSER PANELS(AMM 71-11-02/201).
USE A MIRROR TO EXAMINE THE POSITION INDICATOR ON THEPRECOOLER CONTROL VALVE. THE POSITION INDICATOR IS ON TOP OF THE VALVE (SEE SHEET 6, VIEW B).
 IS THE VALVE IN THE FULL OPEN POSITION?
____ON VALVE WITH MANUAL
NOTE: WRENCHING DRIVE, USE A WRENCH TO OPEN AND CLOSE THE VALVE TO MAKE SURE THAT IT IS NOT STUCK.

YESNO

3 CONNECT A SUPPLY PRESSURE

44 DECREASE THE SUPPLY
GAUGE (Ps), PRESSURE REGULA-PRESSURE (Ps) TO ZERO.
TOR, AND NITROGEN BOTTLE TO REPLACE THE PRECOOLER
THE SUPPLY PRESSURE INLET LINE CONTROL VALVE (AMM 36-12-35/
AT THE TEE FROM THE 5TH-STAGE 401).
DUCT (SEE SHEET 7).

INSTALL A CONTROL PRESSURE
GAUGE (Pc) AND A NEEDLE VALVE
TO THE CONTROL LINE PORT OF
THE PRECOOLER CONTROL VALVE
SENSOR (SEE SHEET 8).

WITH THE NEEDLE VALVE
CLOSED, SLOWLY INCREASE Ps TO
50-60 PSIG.

IS Pc BELOW 11 PSIG?

YES

NO

4 SLOWLY OPEN THE NEEDLE
45 DECREASE THE SUPPLY
VALVE AND REDUCE Pc TO 3 PSI.PRESSURE (Ps) TO ZERO.

DID THE PRECOOLER CONTROL REPLACE THE PRECOOLER VALVE GO TO THE FULLY OPEN CONTROL VALVE (AMM 36-12-35/ POSITION? 401).

YES SEE SHEET 3
(BLOCK 5)

Low Duct Pressure. The Engine Was the Bleed Source.
Figure 104 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
B05771
A

737-300/400/500
MAINTENANCE MANUAL

FROM SHEET 2
(BLOCK 4)
YES NO

5 DECREASE THE SUPPLY
PRESSURE (Ps) TO ZERO.

REMOVE THE CONTROL PRES-SURE GAUGE (Pc) AND THE NEEDLE VALVE FROM THE CONTROL LINEPORT OF THE PRECOOLER CONTROL VALVE AND RECONNECT THE SENSE LINE.
KEEP THE SUPPLY PRESSUREGAUGE (Ps), PRESSURE REGULA-TOR, AND NITROGEN BOTTLE CONNECTED AT THE TEE FOR THE 5TH-STAGE DUCT.
EXAMINE THE POSITIONINDICATOR ON THE PRSOV. IS THE VALVE IN THE FULLY CLOSED POSITION?

YES NO

6 USE A WRENCH TO OPEN AND
CLOSE THE PRSOV.

DOES THE PRSOV MOVE TO THE OPEN AND CLOSED POSITIONSSMOOTHLY?

YESYES
7 PUT THE BLEED SWITCH TO

THE ON POSITION (P5 PANEL). INCREASE Ps TO 70 PSIG. EXAMINE THESE SENSE LINES
FOR LEAKAGE:. SENSE LINE FROM THE BAR TO THE PRSOV (SEE SHEET 9)
. SENSE LINE FROM THE PRSOV TO THE 450`F THERMOSTAT (SEE SHEET 9).
IS THERE ANY LEAKAGE?

NO NO YES

8 DECREASE THE SUPPLY
22 DECREASE Ps TO ZERO.
PRESSURE Ps TO ZERO. DISCONNECT AND CAP THE

REMOVE THE CONTROL PRES-SENSE LINE PORT ON THE PRSOVSURE SENSE LINE AT THE TEE ON THAT LEADS TO THE 450`F THE PRSOV. INSTALL A CONTROL THERMOSTAT (SEE SHEET 10, PRESSURE (Pc) GAUGE AT THE TEE VIEW F). (SEE SHEET 9). INCREASE Ps TO 60-70 PSIG
　
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