GENERAL DESCRIPTION
Page 2-27
CASCADE UNIT - SYSTEM 1 (R-404A) DESCRIPTION
Refer to Refrigeration Diagram in Drawing Section
NOTE: Pressure settings are approximate.
The compressor (item 1) will pump compressed R-404A vapor through the discharge line where the high
pressure gauge displays the pressure of the refrigerant. The high pressure switch (item 95 or item 100)
senses the discharge refrigerant pressure and will open a contact in the event that discharge pressure
exceeds 350 psig. This contact opening will serve to shut down the unit and will automatically reset when the
pressure drops to 250 psig (17.2 barG). The discharge refrigerant vapor enters the condenser.
The condenser (item 5) cools the high pressure R-404A vapor and condenses it into a high pressure liquid.
If the condenser is air-cooled, the condenser fan motor will be energized anytime System 1 is running. If
the unit is water-cooled, the discharge pressure regulator (item 7) will maintain the discharge pressure at
approximately 210 psig (14.5 barG).
High pressure liquid refrigerant exits the condenser and the liquid ! ows through a receiver (water-cooled
units and 1 - 1.5 units only), " lter-drier, sight glass, and into the T.E.V. (item 11) where it changes to a low
pressure two-phase refrigerant. The two phase refrigerant is cold due to the ! ashing of refrigerant. It enters
the cascade condenser (item 13) where the heat from system 2 boils the rest of the R-404A into a vapor.
The cascade condenser serves as the evaporator for system 1. If humidity is called for, some of the R-404A
refrigerant is diverted to the humidity loop prior to entering the T.E.V. See humidity loop section below for
description. Superheated R-404A vapor exits the cascade condenser and moves through the system 1
suction line. A service valve is located near the compressor.
Humidity Loop (Optional Equipment)
When Humidity is called for, the unit runs as a single-stage unit and not a cascade. High-pressure liquid
refrigerant from the condenser, is diverted into two separate paths.
The " rst path is to the liquid-line solenoid (item H49) that feeds liquid refrigerant to the capillary tube (item
H50). The pressure of the refrigerant drops through this capillary tube due to friction and the acceleration of
the refrigerant. The refrigerant exits the capillary tube a two-phase mixture as some of the refrigerant has now
! ashed into vapor. The refrigerant enters the evaporator coil (item 52) and leaves a superheated vapor to the
suction line.
The second path is to the humidity coil solenoid (item H27) that feed liquid refrigerant to the humidity coil
capillary tube (item H23). Two-phase refrigerant exits the capillary tube and enters the wet coil (item H25).
The wet coil is cold enough to attract moisture from the chamber air, but not allowed to get cold enough to
freeze the moisture on the coil. The temperature of the coil is regulated by a pressure regulating E.P.R. valve
(item H26) and is intended to be a ! ooded coil by design. The E.P.R. valve is set at 68 PSIG (4.7 barG), which
corresponds to a 29
°
F/-16°C wet coil temperature. The warm chamber air keeps the moisture from freezing
on the coil. After the E.P.R. valve there is a check valve (item H28) that keeps refrigerant from migrating to
the wet coil when the humidity mode is inactive. The refrigerant leaves the check valve and enters the suction
line, where it remixes with rest of the refrigerant from the " rst path.
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