B. Control
 (1)  The forward cargo compartment heating system operates automatically with power supplied to the airplane. The system operates as described in the above paragraphs.
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A
747-400 MAINTENANCE MANUAL
 FORWARD CARGO COMPARTMENT HEATING SYSTEM - ADJUSTMENT/TEST
__________________________________________________________
 1.  General_______
 A.  This procedure contains one task: a system test of the forward cargo compartment heating system. The test makes sure that the heaters operate when engines are on and compartment temperature is less than 40°F (4°C).
 B.  For a test of the forward cargo compartment temperature sensor refer to (Ref 21-61-00/501).
 C.  The forward cargo compartment temperature switch is installed on the left sidewall of the forward cargo compartment. The switch is installed adjacent to the forward cargo compartment temperature sensor in the sensor assembly box. The switch closes when temperature decreases to less than 40°F (4°C). The switch opens when temperature increases to 50°F (10°C).
 TASK 21-43-00-705-001
 2.  System Test - Forward Cargo Compartment Heating System______________________________________________________
 A.  Special Tools and Equipment
 (1)  G21001-11, Lockout Assembly - N2 Speed Card Test Switch
 B.  Standard Tools and Equipment
 (1)  
Ice pack - or other cold source which can cool a surface to less than 40°F (4°C).

 (2)  
Hot water bottle or other controlled source of heat which can heat a surface to 50°F (10°C) but not more than 185°F (65°C).

 C.  References
 (1)  AMM 24-22-00/201, Manual Control
 D.  Access
 (1)  Location Zone 121 Forward Cargo Compartment Forward Half, LH 122 Forward Cargo Compartment Forward Half, RH
 E.  Procedure
 S 865-002
 (1)  
Apply electrical power (AMM 24-22-00/201).

 S 865-007

 (2)  
Make sure the LOWER LOBE CARGO COND AIR FLOW RATE selector on the P461 panel is in the OFF position.

 S 865-003

 (3)
Set the EQUIP COOLING switch on the P5 overhead panel to STBY.

 (a)  Make sure the equipment cooling inboard exhaust valve is open (Feel for flow of air from the forward cargo compartment heat ducts).
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747-400 MAINTENANCE MANUAL
 S 735-004
 (4)  Do a test of the forward cargo heaters.
 (a)  If the cargo compartment temperature is more than 40°F (4°C) then do these two steps: 1) Remove the coverplate from the forward cargo compartment
 temperature sensor assembly which is installed on the left sidewall at Sta 650.
 2)  Apply the cold source to the probe end of the temperature switch to decrease switch temperature to less than 40°F (4°C).
 CAUTION: OPEN THE PROBE HEAT CIRCUIT BREAKERS THAT FOLLOW BEFORE
_______ THE SUBSEQUENT STEP IS DONE. FAILURE TO OPEN THE PROBE HEAT CIRCUIT BREAKERS CAN CAUSE DAMAGE TO THE HEAT PROBES WHEN THE ENGINES ON SIGNAL IS GIVEN.
 (b)  
Open these circuit breakers on the P6 main power distribution panel. 1) 6C33 AOA HEAT L 2) 6C34 AOA HEAT R 3) 6D28 PROBE HEAT TAT L 4) 6D29 PROBE HEAT TAT R 5) 6D30 PROBE HEAT PITOT L 6) 6D31 PROBE HEAT PITOT R 7) 6D32 PROBE HEAT AUX PITOT L 8) 6D33 PROBE HEAT AUX PITOT R 9) 6D34 PROBE HEAT IND L 10) 6D35 PROBE HEAT IND R 11) 6H19 PROBE HEAT ENG 1 12) 6H23 PROBE HEAT ENG 3

 (c)  
Hold switch S2 on the engine 1 and 3 N2 speed cards (in electrical systems card file M7603) in the TEST position. The N2 speed card test switch lockout assembly can be used to hold the switch in the TEST position.

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