TENNEY ENVIRONMENTAL
EVAPORATOR
COIL
1
The evaporator coil is part of the low stage system in which the liquid refrigerant boils or
evaporates, absorbing heat as it changes into a vapor. The refrigerant fiow to the evaporator is
metered by a capillary tube.
CAPILLARY TUBE
A capillary tube is a length of tubing of small diameter with the internal diameter held to
extremely close tolerances. It is used as a fixed orifice to meter the proper feed of liquid
refrigerant.
THERMOSTAT
A thermostat TS is mounted on the suction
retum line near the low stage compressor to
monitor the temperature of the retum gas flow. When a predetermined high temperature is
reached, the thermostat will energize the Artificial Loading solenoid
14SOL. The setting is
normally 70 degrees Fahrenheit.
LOAD
LIMIT SWITCH
A
high pressure cut-in sensor monitors the pressure inside the low stage compressor
and will activate the Load Limit Switch 4PS when the low stage discharge pressure reaches
280
PSIG.
This will energize the Artificial Loading solenoid 14SOL. 4PS will be deactivated
when the pressure falls to 240 PSIG.
ARTIFICIAL LOADING
In response to the Thermostat switch TS or the Load Limit switch
4PS, the Artificial Loading
solenoid will inject liquid refrigerant into the suction side of the low stage. It will first enter the
expansion tank where the added volume permits the charging of additional refrigerant without
increasing the standby or charging pressure beyond workable limits. Refrigerant gas is then
sucked out of the expansion tank and metered through
a
capillary tube to the suction side of
the low stage compressor. This action will maintain a positive cool refrigerant flow to the
compressor, preventing overheating of the compressor and the discharge gas.
EXPANSION TANK
An expansion tank is provided to add volume to the low stage. Added volume permits the
charging of additional refrigerant without increasing the standby or charging pressure beyond
workable limits. Refrigerant gas is sucked out of the expansion tank during system operation. It
is metered through a capillary tube, regulating the rate of gas entry into the system.
FROSTED LINES ARE TYPICAL,
A
low-stage characteristic is frosted liquid and suction lines. In a normal cascade system, the
liquid line is always below
+32
deg.
F.
The suction line, returning from a -100 deg.
F
evaporator, assuming 15 degree superheat, will also be far below freezing.
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