Operation

sensing element. The switches sense still air temperature. The outboard leading edge overheat warning switches open at approximately 205°F and close at approximately 220°F. The other wing and fuselage overheat warning switches open at approximately 175°F and close at approximately 190°F. High temperature within the leading edge is generally caused by bleed-air leakage or malfunctioning modulator valves. You can detect the portion of the leading edge that has the overtemperature by placing the rotary selector switch, located on the ice control protection panel, to the different sensor positions: INBD, CTR, and OUTBD. (See fig. 3-4.) The temperature at the selected sensor is then read at the indicator adjacent to the rotary switch. An excessive temperature reading on the indicator denotes a malfunction within the area being tested. Operation Figure 3-4, the ice control protection panel, shows a basic diagram of the wing deice system. Each engine is labeled by an engine number. Directly below each engine block (in the diagram) is an OPEN light that illuminates when the bleed- air valve is open 2 degrees or more. The cross- ship manifold from the bleed-air valves goes to each modulating valve and the fuselage shutoff valves. The fuselage bleed-air shutoff valves are normally in the CLOSE position during normal deicing operation. The bleed-air pressure gauge reads cross-ship manifold pressure when one or both switches are opened. A ground air-conditioning switch is located directly under the bleed-air manifold pressure gauge. Located above the switch is an annunciator light, which indicates VALVE OPEN when the ground air-conditioning valve is open. Either one or both fuselage bleed-air shutoff valves must be open to direct air to the ground air-conditioning unit. A leak test switch is mounted on the upper right-hand side of the panel. This switch is used to determine if the leakage of the system is acceptable. Three modulating valve control switches are located on the left side of the wing and empennage ice panel. The outboard switch controls the outboard modulating valve on the left and right wing, the center switch controls the two center modulating valves, and the inboard switch controls the two inboard modulating valves. During normal operation of the deicing system, all four engine bleed-air valves are open to supply bleed air to the cross-ship manifold, and both fuselage bleed-air shutoff valves are closed. Figure 3-4.-Ice control protection panel. 3-5