CSZ ZP 16, Installation, Operation & Maintenance Manual, Page: 35 / 88

GENERAL DESCRIPTION
Page 2-19
The discharge refrigerant vapor passes through the oil separator; the oil separator (item 45) removes the oil in
the refrigerant vapor. It collects the oil and drains it back to the compressor crankcase.
This prevents oil logging in the evaporator. This discharge vapor then passes through the desuperheating
loops. If the unit is air-cooled, the desuperheater (item 45), is part of the air-cooled condenser (item 5). If the
unit is water-cooled, the desuperheater is a separate component. The discharge refrigerant vapor then enters
the cascade condenser. The cascade condenser (item 13) cools the high pressure R-508B/R-23 vapor and
condenses it into a high pressure liquid.
High pressure liquid refrigerant exits the cascade condenser. The liquid fl ows through a fi lter-drier and enters
a tee. The tee will divert some of the liquid refrigerant to be used in the bypass circuit (see last paragraph
of this section). The rest of the refrigerant passes through the liquid line solenoid valve (item 49) and into
the T.E.V. (item 50) where it changes into a low pressure two-phase refrigerant. On 10 HP units and larger,
a min and max valve arrangement is used with two liquid line solenoid valves (Items 49 and 64) and two
T.E.V.s (items 50 and 65), each operating in parallel. The two phase refrigerant is cold due to the
fl ashing
of refrigerant. It enters the distributor (item 51) where the refrigerant is evenly distributed to the evaporator
circuits. The evaporator (item 52) serves to boil the rest of the R-508B/R-23 into a vapor. This boiling action
cools the chamber. System 2 is not in operation during humidity mode. Superheated R-508B/R-23 vapor exits
the evaporator and moves through the system 2 suction line. A service valve is located near the compressor.
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 62) and Hot Gas Bypass Regulator (item 63).
The liquid injection line consists of a Liquid Injection T.E.V. (item 61). The hot gas bypass solenoid (item 62)
will open and close opposite of the liquid line solenoid (item 49). It will allow hot discharge refrigerant vapor to
fl ow directly to the suction line. This is done as a means to control cooling capacity or to “unload” the system.
The liquid injection T.E.V. will sense the temperature of the suction line. It will open automatically 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.
On cascade systems using scroll compressors, there is also a discharge temperature control valve (item 78).
This DTC valve receives liquid refrigerant from the liquid line and injects it into the scroll compressor. This
prevents the compressor from overheating and results in no loss of capacity or mass
fl ow.
CASCADE CONTROL SYSTEM
(Refer to Refrigeration Diagram in Drawing Section)
Mode: Normal cooling/heating
When there is call for cooling the R-508B/R-23 liquid line solenoid (2-SOL) energizes, and the R-404A
compressor turns on. Thirty seconds later the R-508B/R-23 compressor turns on. High pressure switches
(1 & 4 PS) will turn off the compressors if a high discharge pressure is reached on either system. Contact
Cincinnati Sub-Zero’s service department if this occurs. The high pressure switches automatically reset.
When there is a call for cooling 2-SOL is energized. When the chamber is near the set point the controller
begins to cycle 2-SOL on and off. If the controller does not call for cooling for ninety seconds the refrigeration
system will turn off. For heating, solenoid (2-SOL) is de-energized and the heaters are activated.
Mode: Normal cooling (10 hp and above)
When power is applied to the unit, the System 1 crankcase heater (item 93) is on. When there is call for
cooling, the R-508B minimum liquid line solenoid (2-SOL), R-404A minimum liquid line solenoid (7-SOL)
and the R-404A hot gas solenoid (4-SOL) energizes. The R-404A compressor and head fan turn on. Thirty
seconds later the R-508B compressor, head fan, R-508B maximum liquid line solenoid (2-SOL) and the
R-404A maximum liquid line solenoid (1-SOL) turn on. High pressure switches (1 & 4 PS) will turn off the
compressors if a high discharge pressure is reached on either system. Low pressure switches (2 & 5 PS) will
turn off the compressors if a low pressure situation is reached in the suction side of either system. The high
pressure switches are manual reset, and the low pressure switches are automatic reset. If a low oil pressure
situation occurs in either system, the oil pressure safety switch will stop the conditioning system.