Carrier C708, Service Manual

Page: 56 / 148

50
Systems, Controls and Operations
Models C708/C709/C716/C717
COMP LABEL DESCRIPTION FUNCTION BASIC OPERATING LOGIC INPUT /
OUTPUT
EPR Inlet Pressure Upstream
Regulator Limits the minimum
refrigerant pressure in the
hopper (currently set to 60
psig). Limiting the minimum
refrigerant pressure in the
hopper prevents freezing of
product mix on the hopper
wall.
OPR Outlet Pressure Downstream
Regulator Limits the maximum pressure
in the compressor inlet
(currently set to 40 psig). Limiting the inlet pressure to
the compressor helps
prevent overloading of the
compressor.
LIV Liquid Injection Valve Controls the injection of liquid
refrigerant into the suction
line. Liquid refrigerant is injected
into the suction line to lower
the discharge temperature of
the compressor during the
cooling phase of the Heat
mode.
DBV Hot gas discharge bypass
valve. This is an AXV valve. Allows refrigerant to short
circuit – essentially cutting
the capacity of the
compressor when the hopper
alone is being cooled. Refrigerant is passed
through this valve when the
hopper alone is being cooled.
Filter/Dryer This keeps moisture, dirt,
metal, and chips from
entering the refrigerant flow
control valves.
Heat
Exchanger
(sub cooler) This allows the liquid
refrigerant to be cooled
before it reaches the AXV
and TXV. When the liquid is subcooled
before it reaches the
refrigerant control, the
refrigeration effect per unit
mass of refrigerant is
increased.
Receiver The liquid receiver is a
storage tank for liquid
refrigerant. The use of a liquid reciever
makes the quantity of
refrigerant in a system less
critical.