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.
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.
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-