CABIN AIR HIGH-TEMPERATURE LIMIT
THERMOSTAT. The cabin air high-tempera-
ture limit thermostat is a pneumatic control valve
that actuates as a function of cabin inlet air
temperature sensed at the cabin air inlet duct. The
thermostats internal valve opens between 182°
and 200°F and dumps regulated air pressure from
the cabin temperature control valve and the nonice
and low-limit control valve. This induces both
valves to close.
The thermostat uses a temperature-sensing
liquid contained in a sealed-wall probe. Vapor
forms above the liquid, varies in pressure with
surrounding temperature, and actuates a disc
spring that dumps the air pressure supply.
CABIN AIR TEMPERATURE CONTROL
SENSOR. The cabin air temperature sensor,
located mid cabin, consists of two thermistor
probes in parallel that have a nominal 4,000-ohm
resistance at 77°F. The sensor, which operates
over a temperature range of 55° to 85°F, is
connected to the cabin air temperature control,
and it is designed to control cabin temperature
to within ±3°F of the selected temperature.
RAM-AIR SHUTOFF VALVE. The ram-
air shutoff valve (fig. 4-11) consists of a butterfly
valve (9) and linkage. It is opened by a spring and
closed by an air-pressure actuated diaphragm (11).
The diaphragm is activated by a regulated air
Figure 4-11.-Ram-air shutoff valve schematic.