Cooling; Airflow Selection - Cirrus SR20 Pilot Operating Handbook

Cirrus Design
SR20

Cooling

Standard cabin cooling is provided by ram air admitted through the
NACA inlet on the RH cowl to the fresh air valve, mounted to the
forward side of the firewall. When the fresh air valve is open, the air
flows into the cabin mixing chamber. When the fresh air valve is
closed, the cooled air exits into the engine compartment and is
exhausted overboard with the engine cooling airflow.
In Air Conditioning mode (optional), R134A refrigerant enters the
engine mounted compressor as a vapor and is pressurized until the
heat-laden vapor reaches a point much hotter than the outside air. The
compressor then pumps the vapor to the condenser where it cools,
changes to a liquid, and passes to the receiver-drier. The receiver-
drier's function is to filter, remove moisture, and ensure a steady flow
of liquid refrigerant into the evaporator through the expansion valve - a
temperature controlled metering valve which regulates the flow of
liquid refrigerant to the evaporator. Inside the evaporator, the liquid
refrigerant changes state to a gas and in doing so, absorbs heat. The
evaporator then absorbs the heat from the air passing over the coils
and the moisture from the air condenses and is drained overboard
through the belly of the airplane. From the evaporator, the refrigerant
vapor returns to the compressor where the cycle is repeated. During
normal air conditioning operation, ram air from the fresh air intake
flows into the evaporator assembly, is cooled as it passes through the
evaporator coils, and is then ducted forward to the distribution
manifold.

Airflow Selection

The airflow selector on the system control panel regulates the volume
of airflow allowed into the cabin distribution system. When the airflow
selector is moved past the OFF position an electro-mechanical linkage
actuates a valve in the mixing chamber on the forward firewall to the
full open position. The air is then distributed by either ram air or blower
fan to the distribution manifold mounted to the center, aft side of the
firewall. The airflow system modes are as follows: OFF (ram air), 1
(low fan), 2 (medium fan), and 3 (high fan).
P/N 21399-004 P/N 21399-004
Revision A1
Airplane and Systems Description
Section 7
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