The windshield and side window anti-ice system does not let ice, mist, or fog collect on the surface of these areas for a clear view out of the flight compartment.

The windshield and side window anti-ice system includes two windshields and two side windows, which have internal heater elements. There are four electronic heat controllers, one per window, which control power to the heater elements. The anti-ice system is controlled in the flight compartment through the ANTI-ICE control panel.

The windshields and side windows are made with heater elements between the main plies. The heater elements are made with small wires that connect to bus bars, which go across the top and the bottom of the window.

Three temperature sensors between the plies measure the windshield and side window temperature. The temperature sensors are metal wires that show a higher resistance when the temperature increases.

The windshield and side window heating functions are controlled with pushbutton annunciators (PBAs) on the ANTI-ICE control panel and through control/switching functions of four temperature controllers.

---

Each of the two windshields has a temperature controller. The windshield temperature controllers are installed in the forward lower nose compartment in the nose fuselage.

The function of the temperature controller is to control power to the heater element to keep the windshield at a constant temperature. The controller keeps the windshield at a nominal temperature of 93 °F (33.89 °C).

The temperature controller has three solid-state switches, one for each section of the heater element. Each temperature controller has a built-in test (BIT) circuit.

The windshield heater system includes six identical spark gaps that supply protection against lightning effects. There is one spark gap for each windshield heater circuit. Each spark gap has a side connected to the aircraft ground and a side connected to the applicable windshield connection terminal. The spark gap limits the current that can be caused by lightning, to satisfactory levels.

The left temperature controller receives 28 VDC control power from the L MAIN BUS. This temperature controller also receives 28 VDC heater power from the L MAIN BUS to supply the left windshield heater element.

The right temperature controller receives 28 VDC control power from the R MAIN BUS. This temperature controller also receives 28 VDC heater power from the R MAIN BUS to supply the right windshield heater element.

Each windshield temperature controller receives the control power when the applicable L (R) WSHLD/ WINDOW PBA on the ANTI-ICE control panel is not set OFF.

---

Each of the two side windows has a temperature controller. The side window temperature controllers are installed in the forward lower nose compartment in the nose fuselage. The function of the temperature controller is to control power to the heater element to keep the side window at a constant temperature.

The temperature controller keeps the side window at a nominal temperature of 65 °F (18.33 °C). The side window controller has one, low-power, solid-state switch to control the power to one low-power heater element. Each temperature controller has a BIT circuit.

The left temperature controller receives 28 VDC control power from the L ESS BUS. This temperature controller also receives 28 VDC heater power from the L ESS BUS to supply the left side window heater element.

The right temperature controller receives 28 VDC control power from the R AUX BUS. This temperature controller also receives 28 VDC heater power from the R AUX BUS to supply the right side window heater element.

Each side window temperature controller receives the control power when the applicable L (R) WSHLD/WINDOW PBA on the ANTI-ICE control panel is not set OFF.

---

The windshield and side window anti-ice system operates in two different heat modes for the windshield and in one heat mode for the side windows.

Windshield Heat Modes

The heater element for the windshield has three sections (near the side window, in the center, and near the center post).

In most conditions, power is supplied equally across all three sections and is in the low heat mode. When high levels of icing occur, the power to the windshield is supplied in the high heat mode to the center section only. This is because the pilot's line of sight is centered around this section.

When the icing condition occurs, the controller automatically changes from low to high heat mode if more power is necessary for the center section of the windshield.

Side Windows Heat Mode

The temperature controller for the side window heater does not have a high/low heat mode because the heater element for the side window has only one section. It has only a low heat mode which gives anti-fog functions only.

---

Power Supply Control

The windshield and side window anti-ice system is supplied with two types of power:

• 28 VDC heater power
• 28 VDC control power

The control power operates the different control and sensor circuits in the temperature controllers. The heater power supplies electrical power to the heater elements in the windshield and side windows.

Note: 
The temperature controllers must receive control power independently of the heater power. This is because the control power is used to operate the sensors circuits, solid-state switch circuits, and BIT circuits.

Control power is supplied to the anti-ice system through two PBAs on the ANTI-ICE control panel:

• One PBA (L WSHLD/WINDOW) is for the left windshield and side window
• One PBA (R WSHLD/WINDOW) is for the right windshield and side window

When the system is on, the applicable PBA light is off. When the system is set OFF or if the 28 VDC control power is not available, the PBA light comes on to show the OFF legend. Three other PBAs on the ANTI-ICE control panel (L ENG, R ENG, and WING), when set ON, supply discrete signals that are used by the windshield temperature controller to control selection of the heat mode.

Heater power is controlled automatically by the temperature controllers and the applicable protection and switching components (circuit breakers, thermal detectors, relays, and contactors). These protection and switching components are in the left or right circuit breaker panels (LCBP or RCPB) and in the left or right secondary power centers (LSPC or RSPC).

The windshield and side window anti-ice system operate with the following two types of electrical circuits:

• Windshield circuit
• Side window circuit

Windshield Circuit

The left/right windshield temperature controller gets heater power and control power from its respective 28 VDC L (R) MAIN BUS.

The 28 VDC control power for the windshield temperature controllers goes through 5 amp circuit breakers (CB1-E8 in the LCBP; CB2-E8 in the RCBP). Control power is supplied to the temperature controller through the L (R) WSHLD/WINDOW PBAs on the ANTI-ICE control panel.

The 28 VDC heater power or the windshield elements goes through 70 amp thermal detectors (K107 in the LSPC; K106 in the RSPC) and 80 amp contactors (K63 in the LSPC; K64 in the RSPC). From the contactor, 28 VDC heater power is connected to the temperature controller input. The 80 amp contactor gives secondary protection to the system. This prevents more heat than is permitted on the windshield, if the internal controller solid-state switches fail.

The windshield temperature controller is electrically connected to the heater element and temperature sensors in the windshield. The sensor temperature is compared to a 93 °F temperature set point to calculate the power necessary to supply heat to the windshield.

Solid-state switches (control function) on the controller adjust power to the heater element. These switches cycle power on and off to the heater element to adjust the power supplied to the windshield heat element. The windshield controller uses different positions of the three solid-state switches to supply power in the high/low heat mode.

The 80 amp contactor is used for a contactor function and a remote control circuit breaker function. An output of each temperature controller controls one side of the applicable contactor coil. This output gives a ground signal to one side of the coil when the control power is supplied to the controller and there is no fail condition.

Power from the L (R) MAIN BUS is also supplied to the other side of the contactor coil through a 0.5 amp remote circuit breaker (CB1-E9 in the LCBP; CB2-E9 in the RCBP).

When the thermal detector senses greater than 70 amp of current, it causes the 0.5 amp remote circuit breaker to open. This causes the contactor to open and remove power from the heater elements.

Three discrete signals from L ENG, R ENG, and WING PBAs on the ANTI-ICE control panel go to each windshield temperature controller. The temperature controller, through its control logic function, uses the L ENG, R ENG, and WING signals to sense if there is an icing condition.

If one, two, or all three of these PBAs are on, the controller defines that as an icing condition. These de-icing inputs are used by the control logic function in the temperature controllers for the automatic selection of the necessary operating mode.

In addition to the power outputs to the heater elements and the contactor enable signal, each temperature controller supplies (through the BIT function) four discrete signals to the remote data concentrator (RDC) of the EICAS. One signal is then sent to the data concentrator unit (DCU) of the EICAS for crew alerting system (CAS) message display. The other three signals are used by the maintenance diagnostic computer (MDC) to give maintenance messages that identify which line replaceable unit (LRU) is defective.

Side Window Circuit

The left/right side window temperature controller gets heater power and control power from the 28 VDC L ESS BUS.

The 28 VDC control power for the left side window temperature controller goes through 5 amp circuit breakers (CB3-D9 in the LSPC; CB4-D9 in the RSPC). The control power is supplied to the temperature controller through the L WSHLD/ WINDOW PBAs on the ANTI-ICE control panel.

The 28 VDC heater power for the left side window controller goes through a 25 amp circuit breaker (CB3-D8 in the LSPC; CB4-D8 in the RSPC), to a 25 amp relay (K65 in the LSPC). From the relay, the 28 VDC heater power is connected to the temperature controller input.

The right side window temperature controller gets heater power and control power from the 28 VDC R AUX BUS.

The 28 VDC control power for the right side window temperature controller goes through 5 amp circuit breakers (CB4-D9 in the RSPC). Control power is supplied to the temperature controller through the R WSHLD/WINDOW PBAs on the ANTI-ICE control panel.

The 28 VDC heater power for the right side window controller goes through a 25 amp circuit breaker (CB4-D8 in the RSP), to a 25 amp relay (K66 in the RSPC). From the relay, the 28 VDC heater power is connected to the temperature controller input.

The side window temperature controllers are electrically connected to the heater element and temperature sensors in the side window. The sensor temperature is compared to a 65 °F temperature set point to calculate the power necessary to supply heat to the side window.

A solid-state switch (control function) in the temperature controller, sets power on and off to the heater element to adjust the power supplied to the side window.

The relay gives a secondary protection against window overheat in the event that the solid-state switch has a short circuit condition.

In addition to the power output to the heater element and the relay enable signal, each temperature controller supplies (through the BIT function) four discrete signals to the remote data concentrator (RDC) of the EICAS. One signal is then sent to the DCU for CAS message display. The other three signals are used by the MDC to give maintenance messages that identify which line replaceable unit (LRU) is defective.

CAS Messages

The CAS messages related to the windshield and side-window anti-ice system show on the pilot MFD for the conditions that follow:

• L (R) WINDOW HEAT FAIL caution message,if there is a fail condition in the left (right) side window system.
• L (R) WSHLD HEAT FAIL caution message, if there is fail condition in the left (right) windshield system.

The EICAS messages that follow are related to the windshield and side-window anti-ice system

EICAS MESSAGE(S)	LEVEL (COLOR)
L WINDOW HEAT FAIL	CAUTION (amber)
R WINDOW HEAT FAIL	CAUTION (amber)
L WSHLD HEAT FAIL	CAUTION (amber)
R WSHLD HEAT FAIL	CAUTION (amber)

---

The windshield and side window anti-ice system has interfaces with the following components/systems:

• Secondary power center (SPC)
• Anti-ice control panel
• Engine indicating and crew alerting system (EICAS)

  ---

The windshield and side window anti-ice system includes monitor circuits which continuously monitor for incorrect conditions. Each controller supplies four BIT outputs to the RDC. The RDC changes these signals to Aeronautical Radio Inc. (ARINC) data words for the MDC and crew alerting system (CAS).

---

Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
A157	WINDSHIELD TEMPERATURE CONTROLLER (LH)	ZONE(S) 141	30-41-01
A158	WINDSHIELD TEMPERATURE CONTROLLER (RH)	ZONE(S) 142	30-41-01
A159	ASIDE-WINDOW TEMPERATURE  CONTROLLER (LH)	ZONE(S) 141	30-41-05
A160	SIDE-WINDOW TEMPERATURE  CONTROLLER (RH)	ZONE(S) 142	30-41-05

---