*
Right side window heat switch

*
Left backup window heat switch.

The other switches connect to the other WHCU (right forward and left side WHCU).
Each window heat switch has an ON light and an INOP light. The backup window heat switches do not have indications.
These heater circuits are for normal operation:
*
Number 1 window anti-ice heater circuit

*
Number 2 window anti-fog heater circuit

*
Number 3 window anti-fog heater circuit.

The anti-fog heater circuit in the number 1 window is for backup operation.
The WHCU supplies control power to the window heaters. The WHCU also has BITE.
EFFECTIVITY BEJ ALL
Window Heat Enable
The left forward window heat switch enables the anti-ice heater circuit in the left number 1 window. The right side window heat switch enables the anti-fog heaters in the right number 2 and 3 windows.
The INOP lights are on when the window heat switches are OFF. The INOP light shows that the heater circuit is not enabled.
When you push the switches, a mechanical ON label shows switch position. The ON light comes on if the instrument lights system has power. The INOP light goes out to show the heater circuit is enabled.
Window Heat Control
A temperature sensor in each window supplies control feedback to the WHCU. The WHCU controls the temperature of each window independently. The WHCU does not supply power to the heater circuit if the window temperature is too warm.
BITE Operation
The BITE in the WHCU tests for failures in these components:
*
WHCU

*
Heater

*
Temperature sensor.

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FLIGHT DECK WINDOW ANTI-ICE SYSTEM -FUNCTIONAL DESCRIPTION -2

The WHCU can remove all power to a window heater if the BITE in the WHCU finds a failure. The INOP light comes on to show that the heater circuit is not enabled.
There are continuous BITE tests and initiated BITE tests. The continuous BITE tests occur during normal operation. The initiated BITE tests occur during power-up of the WHCU and when you do the window heat ground test on the MAT.
Window Heat Backup
The WHCU supplies electrical power to the anti-fog heater in the number 1 window if the backup window heat switch is ON and either of these conditions exists:
*
Forward window heat switch OFF

*
Forward window heat switch ON and no power to the anti-ice heater in the number 1 window.

A backup temperature sensor supplies feedback.
To remove backup heat from the number 1 window, move the backup window heat switch to the OFF position.
Interfaces
The left forward window heat switch arms the landscape camera window heat. See the landscape camera window heat section for more information (SECTION 30-45).
Training Information Point
To remove power from the window heater circuits, select the window heat switches and the backup window heat switches OFF. You need to do this for safety before you clean the windows or do maintenance on the windows.
The window anti-ice system has burndy blocks on the left of the E1 rack and right of the E2 rack. This lets you switch to the spare sensor if the primary sensor fails.
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FLIGHT DECK WINDOW ANTI-ICE SYSTEM -OPERATION

Window Heat Switches
There are four window heat switches, two for the windows on the left side of the flight compartment, and two for the windows on the right side of the flight compartment.
The left and right forward window heat switches enable the heater circuits in the left and right number 1 windows. The left and right side window heat switches enable the heater circuits for the left and right number 2 and 3 windows.
The left forward window heat switch arms the landscape camera window heat.
See the landscape camera window heat section for more information (SECTION 30-45).
Backup Window Heat Switches
There are two backup window heat switches, one for each of the left and right number 1 windows. The switches are normally in the ON position. The switches have guards. You move the backup window heat switch to the OFF position to remove power from the backup window heat system.
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FLIGHT DECK WINDOW ANTI-ICE SYSTEM -OPERATION

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