AIR CONDITIONING AND PRESSURIZATION
Description
Aircraft Operations Manual
2.1
PAGE
2
Jun 01/18
towards open, the pack valve is moved towards
closed and vice versa. This allows a temperature
regulation of the air leaving the pack.
The cooling part of the pack consists of an air cycle
machine and a dual heat exchanger mounted on
the front end of the air cycle machine. The primary
section of the heat exchanger decreases the tem-
perature of the bleed air from the pneumatic system
before it enters the compressor of the air cycle ma-
chine where the pressure and temperature is in-
creased.
The air is then cooled by the secondary heat ex-
changer section, followed by an expansion over the
turbine of the air cycle machine where further tem-
perature decrease occurs.
The cooled air is then mixed with hot, bypassed air
and with air from the recirculation fan. Before being
distributed, the conditioned air is paced through a
condenser where moisture in the air from the sec-
ondary heat exchanger is condensed using the
conditioned air as a cooling agent. The condensed
water is collected, routed to the heat exchanger and
sprayed into the cooling airstream to improve the
cooling.
Each pack is protected against overtemperature by
two overtemperature switches. One switch is lo-
cated in the compressor outlet duct and closes if
the temperature exceeds 225
C (440
F). The other
switch is located in the pack outlet duct and closes
if the temperature exceeds 82
C (180
F).
If an overtemperature occurs, the respective bleed
valve will close and the DUCT OV TEMP light in the
AIR COND panel will come on together with AIR
COND master caution.
Conditioned air is ducted from the left and right air
conditioning packs. The left pack supplies the cabin
while the right pack supplies cockpit and cabin. The
required supply to the cockpit is limited to 1/3 of the
available flow from the right pack. Therefore, the
supplemental flow from the right pack is routed via
a connecting duct to the cabin ducting.
A small amount of bleed air is routed from Left and
Right Air Conditioning Pack to the Cabin Pressure
Air Filter. The air is blown over the filter to prevent a
moisture build up in the filter.
With Mod. No. 1991 installed, there is a ducting
system from Left and Right air Conditioning Packs
supplying a limited amount of dry air into the tail
−
compartment creating a slight overpressure. By
supplying a stream of dry air flow to the tail
−
compartment a reducing moisture build
−
up in that
area will be achieved.
If a bleed valve is closed or after an engine failure
the air supply is automatically shut off by the Tail
−
compartment Air Shut
−
off Valve (see also AOM
16.1.).
Two recirculation fans feed air from cockpit and
cabin back to the respective pack to improve the
airflow. Filters are provided for cleaning of the recir-
culated air before it enters the recirculation fans.
There is also a recirculation fan fault detection sys-
tem installed. It consists of a speed sensor which
triggers L respectively R RECIRC light in the AIR
COND panel should the speed drop below 80% of
normal speed, indicating failure of the recirculating
fan.
The avionics rack is ventilated by a fan which draws
air from the cabin through a filter into the avionics
rack and down to the underfloor area and then
dumped overboard through the outflow valves. The
avionics vent fan operates whenever anyone of the
three AVION switches is in ON position.
There is also a vent fan fault detection system
installed. It consists of a current detector connected
to the avionics vent fan. The detector activates an
AVIONICS VENT master caution light should the
vent fan stop.
External ground equipment for heating or cooling
can be connected to the distribution system. The
connector is located inside a service door at the
bottom of the fuselage in the rear wing area. The
external ground equipment connection door is pro-
vided with an on the ground (from outside) extend-
able ram air intake. The ram air intake shall be ex-
tended (requires Mod. No. 2305) when dispatching
with only one airconditioning pack operating (MEL
item). The intake is used as a backup if the operat-
ing pack fails. During operation with one Air Condi-
tioning Pack, pressure in the distribution system