TM 1-1520-238-10 2-64 Section X. HEATING, VENTILATION, COOLING, AND ENVIRONMENTAL CONTROL SYSTEMS 2.46 ENVIRONMENTAL CONTROL SYSTEM (ECS). 2.46.1 ECS Description. Crew compartment ventilat- ing, heating, and air conditioning are provided by the ECS. In addition, the ECS is the primary source of conditioned air for the two forward avionics bays (FAB) and the TADS/ PNVS turret. The ECS is comprised of the environmental control unit (ENCU), ECS shutoff valve, ECS control pan- el, and ducting to deliver pressurized air from the engines to the ENCU, and to route conditioned air from the ENCU to the crew stations, FABs, and TADS/PNVS turret. It in- cludes an exhaust fan for the aft avionics bay, one fan in each FAB, and one fan in the electrical power center. The ENCU, located on the left side of the aft equipment bay, produces conditioned air with low moisture content. It takes hot pressurized air from the pressurized air system and cools it through a heat exchange and air expansion process. The ECS shutoff valve receives 28 vdc from the emergency dc bus through the ECS CAB circuit breaker. The FAB fans and aft avionics bay fan receive 28 vdc con- trol voltage from the emergency dc bus through the ECS CAB circuit breaker and 115 vac from the No. 2 essential ac bus through the ECS FAB FANS circuit breaker. In addition, the electrical power center fan and aft avionics bay fan receive 115 vac from the No. 2 essential ac bus through the ECS AFT FAN circuit breaker. All circuit breakers are located on the pilot overhead circuit breaker panel. Thermal switches in the FABs will illuminate the ECS segment on the pilot caution/warning panel if the air temperature in either FAB is greater than 105 5F. The aft avionics bay fan is controlled by a separate automatic thermostat which turns the fan on and off depending on the temperature of the aft avionics bay. 2.46.2 ECS Normal Operation. Operation of the ECS is by the pilot ECS control panel (fig 2-36) located on the pilot left console (fig 2-11) and by the CPG AUX panel (fig 2-33) located on the CPG left console (fig 2-12). Normal operation is as follows: a. ECS Control Panel. The NORM-STBY FAN switch is normally set at NORM. When the switch is set to STBY FAN, the speed of the FAB fans is increased to draw additional air from the crew stations for avionics cooling. The CPG has a two-position STBY FAN switch, located on the AUX panel. This switch is normally in the OFF position to allow the pilot to control the FAB fan speed. When the CPG switch is set to STBY FAN, the speed of the FAB fans is increased. M01-091 Figure 2-36. ECS Control Panel The TEMP control on the pilot ECS panel controls the temperature of conditioned air to the crew stations, FABS, and TADS/PNVS turret. Moving the control between COLD and WARM operates the ENCU temperature con- trol valve that determines the amount of hot pressurized air that will be allowed to mix with conditioned air. Setting the ENCU switch to ON opens the ECS shutoff valve and allows pressurized air to enter the ENCU. In addition, it provides 28 vdc to the temperature control sensor for op- eration of the pilot TEMP control and the ENCU tempera- ture control valve. b. Temperature Control Sensor. The temperature sensor is located in the ENCU outlet duct. It positions the temperature control valve to maintain the selected tem- perature in the crew stations. It receives inputs from the TEMP control on the ECS panel, the FAB thermal switches and the outlet duct air temperature. An output voltage proportional to the difference between the se- lected temperature and the outlet duct air temperature is applied to the temperature control valve to position the valve to maintain the selected temperature. Thermal switches in the left FAB, in conjunction with the ECS panel circuitry, send signals to the temperature control sensor at 75 F and 85 F to reduce the temperature. When the left FAB temperature is below 75 F, the TEMP control estab- lishes the reference voltage sent to the temperature con- trol sensor,