Beechcraft C-12C Operator And Technical Reference Manual page 107

2-78. AIR CONDITIONING.
a. Cabin air conditioning is provided by a
refrigerant gas vapor cycle refrigeration system
consisting of a belt
compressor, installed on the #2 engine accessory pad,
refrigerant plumbing, N
pressure protection
condenser blower, forward and aft evaporator, receiver
dryer, expansion valve, and a bypass valve.
plumbing from the compressor is routed through the
right inboard wing leading edge to the fuselage and
then forward to the condenser coil, receiver dryer,
expansion valve, bypass
evaporator which are located in the nose of the
aircraft. The high and low-pressure limit switches, and
N engine speed switch, are provided to prevent
1
compressor operation beyond required operational
limits. The N speed switch will prevent electrical
1
power from being delivered to the compressor clutch
when engine RPM is below 65% RPM. When the N
speed switch is open and there is a demand for
refrigeration, a green light on the caution/advisory
annunciator panel, AIR COND N
b. The system incorporates over-pressure and
under-pressure protect switches.
over-pressure or under-pressure protect switches will
discontinue compressor clutch and condenser blower
operation, illuminate its respective lockout light/reset
switch located in the nose wheel well, and trip a
7.5-ampere circuit breaker, placarded AIR COND
CONTR, located in the overhead circuit breaker
control panel. When a system shutdown occurs due to
overpressure or underpressure
actuation, the system should be thoroughly checked
before returning it to operation.
c. A second evaporator and blower installation
is located in the fuselage center aisle equipment bay
aft of the rear spar. Environmental air is circulated
through each evaporator automatically in either
manual or automatic control mode.
evaporator blower has a high speed, which can be
selected by the VENT BLOWER switch on the
overhead control panel. A 33 °F thermal sense switch
is installed on the forward evaporator.
switch actuates a hot gas bypass valve, which bleeds
off a portion of the refrigerant from the forward
evaporator, thereby preventing icing of the evaporator.
The forward evaporator and blower will supply the
cockpit, forward ceiling outlets, and forward floor
outlets; while the rear evaporator and blower supply
the aft ceiling outlets, rear floor outlets and toilet
compartment. Both blower circuit breakers are located
in the dc power distribution panel in the lower
equipment bay. A vane-axial blower draws air through
the condenser on the ground.
driven engine mounted
speed switch, high and low
1
switches, condenser
valve, and forward
LOW, will illuminate.
1
Activation of the
protect
The forward
This sense
A 50-ampere circuit
breaker for this blower is located on the dc distribution
panel in the lower equipment bay.
d. When operating under very hot, humid
conditions,
required, the bleed air valves may be left in ENVIRO
OFF until airborne and sufficient altitude is gained.
coil,
2-79. UNPRESSURIZED VENTILATION.
The
Ventilation is provided by two sources.
source is through the bleed air heating system in both
the pressurized and unpressurized mode. The second
source of ventilation is obtained from RAM air through
the condenser section in the nose through a check
valve in the vent blower plenum. Ventilation from this
source is in the unpressurized mode only with CABIN
PRESS switch in the DUMP position. The check valve
closes during pressurized operation.
ventilation is distributed through the main dueling
system to all outlets. Ventilation air ducted to each
1
individual eyeball cold air outlet can be directionally
controlled by moving the ball in the socket. Volume is
regulated by twisting the outlet to open or close the
valve.
2-80. ENVIRONMENTAL CONTROLS.
An environmental
overhead control panel provides for automatic or
manual control of the system. This section contains all
the major controls of the environmental function
including bleed air valve switches, a vent blower
control switch, an aft vent blower switch, a manual
switch
temperature switch for control of the heat exchanger
valves, a cabin temperature level control, and the
cabin temp mode selector switch for selecting
automatic heating or cooling or manual heating or
cooling. Four additional manual controls on the main
instrument subpanels may be utilized for partial
regulation of cockpit comfort when the cockpit partition
door is closed and the cabin comfort level is
satisfactory.
a. Heating Mode.
(1) If the cockpit is too cold:
1. PILOT and COPILOT AIR knobs – As
2. DEFROST AIR knob – As required.
3. CABIN AIR – Pull out in small
TM 1-1510-218-10
where maximum air
control
required.
increments. Allow 3–5 minutes after
each adjustment
stabilize.
conditioning is
One
Ram air
section on the
for system to
2-91