System Operation

System Operation The rain-removal system is activated by placing the windshield switch in the AIR position. With the switch in the AIR position, a 28-volt dc circuit is completed from the air-conditioning circuit breaker, through the windshield switch, to the solenoid of the rain-removal pressure- regulator shutoff valve, to the nosewheel well bleed-air relay, and to the windshield rain-removal warning relay. When the nosewheel well bleed- air relay is energized, the 115-volt ac circuit from the bleed-air circuit breaker, through the AUTO position of the nosewheel well bleed-air switch, is completed to the open windings of the nosewheel well bleed-air shutoff valve. With the circuit completed, the windshield air caution light will illuminate. When you move the windshield switch to the OFF position, the windshield air caution light will go out. The nosewheel well bleed-air shutoff valve directs the 115-volt ac power to the close windings of the motor. The weight-on-wheels switch will energize the nosewheel well bleed-air relay. When the rain-removal pressure-regulator shutoff valve solenoid is energized, the valve opens and allows pressure-regulated (75±3.5 psi) hot bleed air to flow to the ejectors of the rain- removal nozzles. To lower the temperature of the hot bleed air, the ejectors draw cool air from the nose radome compartment. The cool air and hot bleed air mix in the plenum of the nozzle assembly. The air passes through the plenum to 26 nozzles, which direct the hot air in a wide stream across the windshield. 3-10