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Anti-Ice/Rain Removal Module
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 A.  The four NACELLE ANTI-ICE control switches are located in the anti-ice-rain removal module M7321 on the P5 overhead panel. Each switch has 3 positions to place the corresponding engine inlet anti-ice system on, off, or in automatic mode under control of the ice detection system (Ref 30-81-00).
Engine Inlet Anti-Ice Valve
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 A.  The engine inlet anti-ice valve regulates the flow of heated air into the anti-ice duct. The 3.5-inch butterfly type valve is solenoid operated and regulates pressure from 20 to 28 psig when opened.
 B.  The valve is normally closed when no power is applied. When the solenoid is energized, the butterfly is open for airflow and a pilot regulator in the valve senses the downstream (outlet) static pressure and modulates the inlet pressure admitted to the actuator piston. The piston positions the butterfly to maintain an outlet static pressure of 20-28 psig. If valve inlet pressure drops to 13-20 psig, the valve is fully open. If valve inlet pressure drops below 13 psig, the valve will close, overriding electrical control.
 C.  The valve has a manual override knob and an open/close hex stud. The valve may be manually opened or closed and can be locked in either position. The override knob has a position pointer which indicates whether the valve is in normal open or closed position, or in locked open or locked closed position.
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 30-21-00
 ALL  ú ú 04 Page 1 ú Oct 10/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

747-400
MAINTENANCE MANUAL

SEE  A  NACELLE 1  32 AUTO OFF ON AUTO WING ANTI-ICE OFF ON  4 ANTI-ICE 
A 
FLIGHT COMPARTMENT 
ANTI-ICE DUCTS  STRUT BLEED AIR DUCT 
OVERHEAT SWITCH ENGINE COWL 
ANTI-ICE CONTROL VALVE 
SPRAY TUBE  EXHAUST PORT  SWITCH PRESSURE NOSE COWL 
Figure 1 Engine Inlet Thermal Anti-Ice System - Component Location 

M49163
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 30-21-00
 ALL  ú ú 08 Page 2 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 D.  A valve position switch internal to the valve is mechanically actuated to close when the valve is open. This provides valve position information to the flight deck.
 4.  Nose Cowl Pressure Switch
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 A.  The nose cowl pressure switch is mounted on a threaded boss on the anti-ice duct downstream of the anti-ice valve. The switch contacts close at 30 to 39 psig with increasing pressure and open at 30 psig with decreasing pressure in the ducts. When the switch closes, the EICAS status message ANTI ICE NAC 1, 2, 3, or 4 is displayed to indicate that the valve is not regulating outlet pressure below the 30 psig limit.
 5.  Engine Cowl Overheat Switch
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 A.  The engine cowl overheat switch is mounted on the fan cowl support beam. If ambient air temperature inside the cowl exceeds 250 |5° F, the switch contacts will close, energizing and latching the fan case overtemp relay, which will close the anti-ice valve until air temperature drops below 250° F and the engine inlet TAI system is turned off and back on. When the switch closes, the EICAS advisory message NAI DUCT 1, 2, 3, or 4 LEAK is displayed.
 6.  Operation (Figs. 2 and 3)
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 A.  Functional Description
 (1)  
The 28-volt dc APU battery bus supplies operating voltage to the control switches in the anti-ice-rain removal module. When the ice detection system activates the engine inlet anti-ice system or the control switch is in the ON position, 28 volts dc is applied to the anti-ice valve, causing the valve to open. When open, the valve regulates pressure into the anti-ice duct to 20-28 psig.

 (2)  
When the valve opens, the position switch in the valve closes and the letters NAI appear in green to the left of the engine N1 indicator on the main EICAS. If valve position does not agree with the position commanded by the ice detection system or the control switch, the EICAS advisory message NAI VALVE 1, 2, 3, or 4 appears along with the status message ANTI ICE NAC 1, 2, 3, or 4.
　
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