ENVIRONMENTAL CONTROL PANEL

supply that is controlled by a fluidic control system or a torque motor and flapper (5), depending upon whether the solenoid is energized or de-energized. During the ram-air augmentation mode (auto- matic mode), the ram-air shutoff valve regulates downstream pressure to a fixed differential of 7.5 ± 2 inches of water above cabin pressure. The automatic mode is selected by energizing the solenoid. This allows the fluidic control to establish the differential across the valve actuator as determined by valve downstream pressure (6) and cabin pressure (1). During manual operation (override mode), the auxiliary vent switch on the environmental panel is used to place the ram-air shutoff valve in any position from fully closed to fully open by varying electrical power to the valve torque motor. In the override mode, selected by de-energizing the solenoid, power is applied to the torque motor to close the pneumatic supply pressure nozzle and to open the vent nozzle, thereby lessening the ram- air shutoff valve actuator closing pressure. This permits the actuator spring to move the butterfly toward an open position. RAM-AIR HIGH-AND LOW-TEMPERA- TURE LIMIT SWITCH.— The ram-air high- and low-temperature limit switch senses air tem- perature at the ram-air inlet duct. There are two circuits in the ram-air high- and low-temperature limit switch that are normally closed. One circuit opens with decreasing ram-air temperature, and the other opens with increasing ram-air tempera- ture. The ram-air high- and low-temperature limit switch circuitry is interconnected with the bleed- air flow control valve, the ram-air shutoff valve, and the auxiliary vent switch. The ram-air high- and low-temperature limit switch operation controls the ram-air shutoff valve position when the ram-air shutoff valve is operating in the automatic mode. GROUND AIR SUPPLY CHECK VALVE AND GROUND COOLING AIR CONNEC- TOR.— Support equipment provides low-pressure conditioned air when it is attached to the ground cooling air connector. The connector is located on the right side of the aircraft in the right wheel well at fuselage station (FS) 465. It is accessible through a hinged door on the underside of the sonobuoy deck. The connector consists of a silicone-impregnated nylon hose and a clamp supporting the air check valve. The ground air check valve is a 4-inch diameter, split-flapper valve spring-loaded to the closed position. Ground cooling air opens the check valve and closes the ram and recirculated air check valves. The ground source low-pressure air bypasses the refrigeration unit and enters the cabin area because the air-conditioning system is not used when low-pressure ground air is connected. Therefore, the bleed-air flow control valve will be closed. ENVIRONMENTAL CONTROL PANEL The environmental control panel (fig. 4-12) is located on the center console and is used by the flight crew to control temperature, pressurization, and anti-icing functions. The discussion of this panel is limited to the ram-air valve position selector, air-conditioning switch, and the cabin air temperature selector. Ram-Air Valve Position Selector When the ram-air valve position selector (AUX VENT switch) is placed in the OFF position, the automatic mode is established by way of the fluidic control system. Clockwise rotation towards the ON position overrides logic controls of the air-conditioning system. Control of the ram-air shutoff valve is determined by the Figure 4-12.-Environmental control panel. 4-18