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Copyright © 2020
Original Release
ATA 21‐00‐60
Page | 11
2.1.5. Refrigerant recovery/recycling service equipment must be approved for use with R-134A
refrigerant. Recycling machines must be approved by Underwriters Laboratories (UL) and
meet SAE standard J2210 and SAE standard J2099 for refrigerant purity.
2.2. System Description and Operation:
2.2.1. The cabin cooling system installed in the Pilatus PC12 M19 Aircraft operates using a
closed vapor cycle concept using refrigerant R-134A as the heat absorption media. The R-
134A 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 1 (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 controller drives the R-134A compressor at a variable speed (dependent
upon current cooling requirements) which compresses the R-134A 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 R-134A 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.
