Component Maintenance Manual
EFFECTIVITY: ALL
21-00-22
Introduction
Page
12
JULY 21, 2011
2.1.5
Refrigerant recovery/recycling service equipment must be approved for use with R12
refrigerant. Recycling machines must be approved by Underwriters Laboratories (UL) and
meet SAE standard J2210 and SAE standard J2099 for refrigerant purity.
SUBTASK 21-00-22-99F-007
2.2
System Description and Operation:
2.2.1
The cabin cooling system installed in the Pilatus PC12 Aircraft operates using a closed
vapor cycle concept using refrigerant R12 as the heat absorption media. The R12 air
conditioning system cools the aircraft in a similar manner as systems found in an
automobile or home. However, aircraft air conditioning systems contain components which
are designed to be light weight, compact, provide high performance, and provide the ability
to operate at extreme altitudes and ambient temperatures.
2.2.2
The concept of air conditioning a room, cabin or cockpit is straight forward. An example of a
system is shown in Figure 2 (refer to Schematic and Wiring Diagrams, Section 4).
Refrigerant is the media which absorbs and rejects the room or cabin heat. By continuous
recirculation of the warm cabin air, heat is absorbed in the evaporator module(s) and is
rejected to the outside through the system condenser. When the system is turned on, the
electric motor drives the R12 compressor at a constant speed and capacity which
compresses the R12 refrigerant gas to a high pressure. The hot, high pressure gas then
passes through the condenser coil where it is cooled and condensed into a warm liquid at
constant pressure. The warm liquid is then routed into a receiver-dryer container where the
liquid and any remaining gas are separated and any moisture is absorbed. The warm, dry
liquid is then directed to the evaporator module expansion valve where the high pressure
liquid is expanded to a low pressure. The expansion process creates a super cool gas
which passes through the evaporator coil and absorbs heat from the warm cabin air passing
over the coils. The warm low pressure refrigerant then enters the R12 compressor where
the process starts all over again. In addition to cooling the cabin air, a refrigerant type
system also removes a large percentage of the moisture in the air as well as removing dust
and pollen particles in the air. Thus, the system conditions the air as well as cooling it. As a
safety feature, the unit is also equipped with a binary pressure switch. This switch prevents
the unit from operating if the discharge pressure becomes excessively high. The switch
also prevents the unit from operating if the internal pressure is very low due to leakage or
low ambient temperatures.
