LIQUID INJECTION OVERVIEW
Scroll compressors require liquid injection
when applied in low temperature applications.
Liquid injection is only available with ZF
models. The liquid injection controls introduce
a steady volume of refrigerant midway
through the compression process to reduce the
temperature of the scrolls. Unlike traditional
injection systems on reciprocating compres-
sors, this does not reduce the refrigeration
capacity of a scroll compressor. A precision
sized capillary tube meters more liquid
refrigerant as condensing pressure rises.
Refrigeration flow to this capillary tube is
controlled by a solenoid valve. A current
sensing relay should be wired in series with
the solenoid valve coil (3-6 hp only). This will
halt liquid flow in the event of a compressor
protector trip.
SUBCOOLING
Autosurge for Ambient Subcooling
The
Autosurge Valve
directs the flow of refrig-
erant either
through the Receiver
(Flow
Through), or
around the Receiver
(Surge) in
response to ambient subcooling obtained in the
condenser.
The Autosurge Valve reacts to the condensing
pressure through its equalizer line, and to the tem-
perature of the liquid refrigerant returning from
the Condenser through a bulb mounted on the
Liquid Return Line up stream of the Flooding
Valve. When the refrigerant temperature returning
from the condenser drops below its condensing
temperature, the system has ambient subcooling.
The valve is factory set at 10Þ F of subcooling
and is
not
field adjustable.
MECHANICAL SUBCOOLING
By lowering the temperature of the liquid sup-
plied to the TEV, the efficiency of the evaporator
is increased. The lower temperature liquid refrig-
erant has more heat absorption capability, and can
therefore remove more heat with less refrigerant.
Mechanical subcoolers are able to maintain con-
sistent liquid temperatures year round, and are not
limited by seasonal conditions.
A liquid line solenoid valve and a TEV control
refrigerant to the subcooler. An EPR is often used
to prevent the subcooler suction temperature from
dropping below freezing.
Electrically, a thermostat responding to the main
liquid line temperature cycles the solenoid valve
on the liquid supply.
September 1, 1997
P/N 401789
2 - 9
HUSSM ANN CORPORATION • BRIDGETON, M O 63044-2483 • Printed in USA
Figure 2-16 —Liquid Injection Schematic
Dual
Pressure
Control
Cap Tube
Assembly
Condenser
Scroll
Compressor
Filter/Drier
Receiver
Discharge
Thermostat
Solenoid Valve
S
X
TEV
Evaporator
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