water separator inlet. The temperature controller then
The temperature indicator, TEMP C, and the
positions the three airflow control valves in a
three-position TEMP SELECTOR switch are
programmed schedule to properly blend the hot, warm,
connected to read three different temperature sources as
and cool air flowing in the air cycle cooling system to
follows:
obtain the selected flight station or cabin temperature.
FLT STA COND AIR position. Temperature of
The temperature control system employs the basic
the conditioned air leaving the air cycle cooling system,
air cycle cooling system, two valve-controlled bypass
which is controlled to meet flight stations requirements.
ducts, and one shutoff valve. The hot air bypass valve
CABIN COND AIR position. Temperature of
(valve C) controls the amount of hot primary
the conditioned air leaving the air cycle cooling system,
compressor discharge air that will be bypassed around
which is controlled to meet cabin requirements.
the air cycle cooling system. The turbine bypass valve
(valve A) controls the amount of warm air that will be
CABIN TEMP position. Temperature of the air
bypassed around the turbine refrigeration unit. The
leaving the cabin, exhaust air temperature, which is
turbine shutoff valve B controls the volume of air
actual cabin temperature.
flowing through the turbine refrigeration unit for
cooling.
OPERATION
When full cold is commanded, all of the airflow
The P-3 aircraft is equipped with two temperature
into the air cycle cooling system is being cooled in the
control systems, one for the flight station and one for
turbine refrigeration unit. If the control system
the main cabin area. Each temperature control
demands heating, warm or hot air will bypass various
system consists of a temperature controller, a
portions of the air cycle cooling system until the desired
selector-indicator, a master temperature sensor, a duct
temperature is obtained. The valve B and C operation
rate sensor, and three airflow control valves.
schedules are similar in response, but opposite in
direction. On the other hand, valve A has a relatively
To operate the temperature control system, the
complicated operation schedule. This is because valve
flight crew sets the selector-indicator at the desired
A controls the bypass of air that is warm, but close to a
temperature (fig. 6-8). This information is transmitted
comfortable temperature.
to the temperature controller, along with signals from
the sensors that provide the actual cabin or flight station
Under certain atmospheric conditions, water
temperature and the rate of temperature change at the
separator bag icing will cause reduced airflow and high
Figure 6-8.--Selector-indicator.
6-10
