(8)  
If insulation was removed, apply insulation as in para. 2.

(9)  
Install duct clamps removed above.

(10)
Reinstall items removed to gain access.

500 
21-24-11 Page 802  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/98 

GASPER FAN - REMOVAL/INSTALLATION
1.  General
A.  The gasper fan is located in the conditioned air distribution bay. Access is through the aft bulkhead of the forward cargo compartment.
2.  Prepare for Removal
A.  Position GASPER FAN switch (P5) OFF.
B.  Open GASPER FAN circuit breaker (P6).
C.  Remove lower cargo compartment aft bulkhead access panel. (Ref 25-52-131).
3.  Remove Gasper Fan (Fig. 401)
A.  Remove electrical connector.
B.  Remove ground strap, if installed.
C.  Support fan and remove clamps securing fan to ducts.
D.  Cover open ducts to prevent ingestion of foreign objects.
4.  Install Gasper Fan (Fig. 401)
A.  Remove duct protective covers.
B.  Position fan in duct opening with electrical connector aft. Install clamps loosely.
C.  Position fan so that electrical connector may be installed with no stress on wires. Tighten clamps.
D.  Install grounding strap. Maximum resistance 0.010 ohms. (Ref 20-20-1 MP).
E.  Install electrical connector.
5.  Test Gasper Fan
A.  Provide electrical power (Ref 24-22-00 MP).
B.  Close GASPER FAN circuit breaker (P6).
C.  Position GASPER FAN switch (P5) ON.
D.  Check that gasper fan operates and air is discharged from PSU gasper outlets in control and passenger cabins.
E.  Position GASPER FAN switch (P5) OFF.
6.  Restore Airplane to Normal
A.  Install lower cargo compartment aft bulkhead access panel (Ref 25-52-131).
B.  Remove electrical power if no longer required. (Ref 24-22-00 MP).
500 
Oct 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-24-21 Page 401 

H18898
Gasper Fan Installation  500 
21-24-21  Figure 401  Oct 20/85 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

PRESSURIZATION CONTROL - DESCRIPTION AND OPERATION
1. General
A.  Pressurization control includes the pressurization control system, pressurization relief valves, and pressurization indication and warning.
2.  Pressurization Control System
A.  The pressurization control system describes only the parts of pressurization control which provide a regulated low altitude pressure in the cabin at all airplane altitudes.
B.  The system is electrically operated and electronically controlled. There are four operating modes, which may be selected on the pressure control panel. Automatic is the normal operating mode, standby is semi-automatic in operation and backs up the automatic system, and two manual modes provide direct electrical control. All modes position the cabin pressurization outflow valve to maintain desired cabin pressure.
(1)  The manual modes are identified as manual AC and manual DC. Each provides direct control to the outflow valve through separate electrical motors. The manual modes backup the automatic and standby systems.
C.  In each of the three systems, cabin pressure is maintained by positioning the outflow valve to regulate airflow from the cabin with respect to air from the air cycle system.
3.  Pressurization Relief Valves
A.  Pressurization relief valves are valves or equipment installed for the purpose of relieving abnormal conditions which prevent normal operation of the airplane.
B.  Relief valves include safety relief valves, a pressure and relief valve, pressure equalization valves, and blowout panels.
4.  Pressurization Indication and Warning
A.  Pressurization indication and warning describes the equipment provided for monitoring cabin pressure and cabin pressure rate of change and the equipment provided for cabin altitude warning.
500 
Nov 15/68  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-30-0 Page 1 

K16665
 Pressurization Control Schematic  516 
21-30-0Page 2   Figure 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/99 

PRESSURIZATION CONTROL SYSTEM - DESCRIPTION AND OPERATION
1.  General
A.  The pressurization control system is an electrically operated and electronically controlled system, which meters the exhaust of ventilating air to provide controlled pressurization of the passenger and control cabins, the electronic compartment, both cargo compartments, and the lower nose compartment. The pressurization control system consists of a pressure control panel, a pressure controller, and a cabin pressurization outflow valve (Fig. 1). The pressurization control system characteristics are as follows:
　
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