(4)  
Set INS BAT PARALLEL switch on flight engineer's panel P4 to NORMAL position.

 (5)  
Close circuit breaker on front panel of INS battery units 1 and 3.

 (6)  
Remove standby dc power, equipment cooling, and airplane power if no longer required. Refer to 24-33-00, 21-58-00, and 24-22-00.

 EFFECTIVITY

 
 ALL  02 Page 503  Apr 25/9134-41-11
 INS COOLING FAN - REMOVAL/INSTALLATION
______________________________________
 1.  General
_______
 A.  An INS cooling fan is mounted below each INS navigation unit in the throat of the cooling air exhaust plenum. The fan is held in place by four screws and is powered through a permanently attached cable connecting to terminal blocks at the rear of the plenum.
 2.  Referenced Procedures
_____________________
 A.  34-41-03, Removal/Installation
 B.  34-41-12, Adjustment/Test
 3.  Remove INS Cooling Fan (Fig 401)
______________________
 A.  Remove appropriate INS navigation unit (Ref 34-41-03).
 B.  Lift out screen covering cooling air exhaust plenum.
 C.  Disconnect three fan cable wires from terminal blocks and remove fan and cable clamp.
 4.  Install INS Cooling Fan (Fig 401)
_______________________
 A.  Mount fan in cooling air exhaust plenum. Orient fan so cable exits towards right side of airplane.
 NOTE: Fan assembly extends down into throat of plenum.
____
 B.  Install cable clamp.
 C.  Attach three fan cable wires to terminal blocks.
 NOTE: Green wire goes to G3, red wire to G2 and yellow wire to G1.
____
 D.  Set screen in place over cooling air exhaust plenum.
 E.  Test INS cooling fan by performing INS cooling system test (Ref
 34-41-12).

 EFFECTIVITY

 
 ALL  01 Page 401  Oct 10/7334-41-12
SEE A SCREEN
INS COOLING FAN
FAN GASKET
FWD
SCREEN BRACKET
COOLING FAN
CAPACITOR

A

INS Cooling Fan - Removal/Installation
Figure 401

754952
EFFECTIVITY

701 Page 402
ALL 34-41-12
 Oct 10/73
 INS COOLING FAN - ADJUSTMENT/TEST
_________________________________
 1. INS Cooling System Test
_______________________
 A. General
 (1)  The following procedure provides instructions for testing the INS cooling fan and airflow seal.
 B. Referenced Procedures
 (1)  
21-58-14, Equipment Cooling Racks - Inspection/Check

 (2)  
24-22-00, Manual Control - Maintenance Practices (Apply Power)

 (3)  
34-41-03, INS Navigation Unit - Removal/Installation

 C. Equipment and Materials
 (1)  Mechanics scale, graduated in hundredths of an inch
 D. Prepare for Test
 (1)  
Provide electrical power. Refer to 24-22-00.

 (2)  
Remove appropriate INS navigation unit (if not previously removed). Refer to 34-41-03.

 E. Test INS Cooling System (Fig. 501)
 (1)  Open normal and alternate equipment cooling circuit breakers on main power center panel P15.
 CAUTION: RESET EQUIPMENT COOLING CIRCUIT BREAKERS AS SOON AS THE
_______ TEST OF EACH INS FAN IS COMPLETED TO RESTORE COOLING OF OTHER RACK UNITS.
 NOTE: Main power center panel P15 is located on starboard side of
____ airplane in main equipment center.
 (2)  Remove lift-out screen.
 CAUTION: DO NOT POKE OBJECTS INTO THE FAN ASSEMBLY TO DETERMINE
_______ DIRECTION OF ROTATION; WAIT UNTIL MOTOR SLOWS DOWN AND OBSERVE BY VISUAL INSPECTION.
 (3)  
On electronic circuit breaker panel P7 or P126, close the pair of 115-volt ac power circuit breakers to removed navigation unit (PWR-INS 1 for system 1, PWR-INS 2 for system 2 or PWR-INS 3 for system 3).

 (4)  
Wait for fan to pick up speed (3 to 5 seconds) and open circuit breakers closed in step (3).

 (5)  
Verify that INS cooling fan rotates in a counterclockwise direction when viewed from top of tray.

 NOTE: Rotational direction is most easily observed as the fan
____
 slows to a stop.

 (6)  
Replace lift-out screens.

 (7)  
Close circuit breakers opened in step (1).

 (8)  
Check airflow seal for damage (Fig. 501)

 (9)  
Replace airflow seal if torn or deformed sufficiently to prevent a good air seal to bottom of INS navigation unit. Refer to 21-58-14.
　
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