GENERAL DESCRIPTION
35
If the chamber is equipped with a Low RH package, the following description applies. When
dehumidification is called for, some of the liquid refrigerant is diverted to the humidity loop. The
refrigerant passes through a solenoid valve (item H131), and a Low RH thermostatic expansion valve
(item H130). Two phase refrigerant exits the thermostatic expansion valve and enters the evaporator
(item H125). The evaporator temperature is cold enough to freeze water out of the air where it collects
and freezes on the surface of the evaporator. The temperature of the evaporator is able to drop below
freezing temperature due to the suction bypass solenoid (item H129) where it allows the suction vapor
to bypass the evaporator pressure regulator valve (item H126). This allows the chamber to achieve low
temperature dew points limited, as previously discussed in this manual.
Bypass Loop
The bypass circuit is composed of two lines in parallel: the hot gas bypass line, and the liquid injection
line. The hot gas bypass line consists of a solenoid valve (item 117) and a hot gas bypass regulator
valve (item 118). The liquid injection line consists of a liquid injection solenoid valve (item 121) and
liquid injection thermostatic expansion valve (item 123). The hot gas bypass solenoid valve (item 117)
will open and close opposite of the liquid line solenoid valve (item 110) (2 HP – 3.5 HP). The hot gas
bypass solenoid valve (item 117) will open and close opposite of the liquid line solenoid valve (item
119) (6 HP – 15 HP). The valve will allow hot discharge refrigerant vapor to flow directly to the suction
line. This is done as a means to control cooling capacity or to “unload” the system. The liquid
injection thermostatic expansion valve will sense the temperature of the suction gas and will
automatically open to feed liquid refrigerant into the suction line. This will provide cooling for the hot
gas that is being fed into the suction line. The cooling effect keeps the compressor from overheating.
There is also a discharge temperature control valve (item 178). This prevents the compressor from
overheating and results in no loss of capacity or mass flow.
TUNDRA® CONTROL SYSTEM
Refer to Refrigeration Diagram in Drawing Section.
Mode: Normal cooling/heating (2 HP – 3.5 HP systems)
When there is a call for cooling, the R-410A liquid line solenoid (101-SOL), and the liquid injection
solenoid (108-SOL) energize. The R-410A compressor turns on (2 HP – 3.5 HP). The high pressure switch
(101-PS) will turn the compressor off if a high discharge pressure event is reached. Contact Cincinnati
Sub-Zero’s service department if this occurs. The high pressure switch will automatically reset. When
there is call for cooling, (101-SOL) is energized. When the chamber is near the set point, the controller
begins to cycle (101-SOL) on and off. At the same time, the R-410A hot gas bypass solenoid (109-SOL)
cycles on and off opposite of (101-SOL). If the chamber does not call for cooling for ninety seconds, the
refrigeration system will turn off.
When there is a call for heating, (101-SOL) will de-energize and the heaters will energize.
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