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DRAIN MAST HEATER - MAINTENANCE PRACTICES
1. General
A. The replacement of a drain mast heater requires removal and disassembly of the drain mast (Ref Chapter 38, Waste Water Drain Mast and Heater - R/I).
B. Normal drain mast anti-icing is accomplished using 28 volts ac on the ground and 115 volts ac when airborne. If excessive icing persists on the drain mast(s) the procedure in par. 2 may be used to simulate airborne conditions to melt the ice using 115 volts ac.
CAUTION: USE 115 VOLTS AC ON THE GROUND ONLY LONG ENOUGH TO MELT ABNORMAL AMOUNTS OF ICE. EXCESSIVE USE OF SYSTEM COULD DAMAGE COMPONENTS DUE TO OVERHEATING.
2. Ground Anti-Icing Using 115 Volts AC
A. Set APU GENERATOR 1 and 2 switches on P5-4 panel to ON position.
B. Open EXTERNAL BUS PROTECTION circuit breaker on P6-12 panel.
C. On Ell landing gear logic shelf, depress AIR SENSING test switch.
D. Immediately after anti-icing is accomplished, return airplane to normal by closing switches and circuit breakers opened at start of procedure.
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WATER AND TOILET DRAIN ANTI-ICING SYSTEM - ADJUSTMENT/TEST
1. Toilet Drain Anti-Icing System
A. General
(1) The following test gives the procedure for testing the toilet drain heaters.
B. Test Toilet Drain Heaters
(1)
Check that drain heater circuit breaker on P18 panel is open.
(2)
Provide electrical power.
(3)
Close drain heater circuit breaker on P18 panel and check by hand that toilet drain fitting and cap are being heated.
(4)
Open drain heater circuit breaker.
(5)
If no longer required, remove electrical power from airplane.
2. Water and Toilet Drain Anti-Icing System Test
A. General
(1) To test toilet and drain mast heaters, the airplane must be resting in a normal attitude. To test the operation of the landing gear air safety sensing relay in the drain mast heater circuit refer to Chapter 32, Landing Gear Air - Ground Sensing.
B. Test Toilet Drain and Drain Mast Heaters
(1)
Check that DRAIN MAST - AIR and DRAIN MAST - GRD circuit breakers on P18 panel are closed.
(2)
Check that LANDING GEAR LIGHTS circuit breaker on P6 panel is closed.
(3)
Check that STALL WARN-1-AC circuit breaker on P18 panel is open.
(4)
Provide external power.
(5)
Check that drain mast is moderately warm.
(6)
Provide APU electrical power.
(7)
Remove external electrical power.
(8)
Open the circuit breaker on the G7 bus protection panel for approximately 2 minutes.
(9)
Check that drain mast remains moderately warm.
(10)
Press AIR SENSING test switch on M338 landing gear module (on E3-2 shelf) for approximately 20 seconds.
CAUTION: DO NOT LEAVE THE DRAIN MAST IN THE HOT CONDITION FOR MORE THAN 20 SECONDS.
(11)
Check that the drain mast becomes extremely hot.
(12)
Release the AIR SENSING TEST switch and close the circuit breaker on the G7 panel.
(13)
Close STALL WARN-1-AC circuit breaker on the P18 panel.
(14)
Provide external electrical power if required.
(15)
Remove APU electrical power and shut down APU.
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