IM 738-2 89
Unit Options: Hot Gas Bypass
Hot Gas Bypass
Hot gas bypass is a system for maintaining evaporator pressure
at or above a minimum value. The purpose for regulating the
hot gas into the distributor is to keep the velocity of the
refrigerant as it passes through the evaporator high enough for
proper oil return to the compressor when cooling load
conditions are light.
The system consists of a combination of solenoid valves and a
pressure
regulating valve as shown in Figure 89. The solenoid
valves are factory wired to open whenever
the controller calls
for the first stage of cooling. The pressure regulating valve
starts to modulate open at 57 psig (393 kPa).
The regulating valve opening point can be determined by
slowly reducing
the system load or reducing the required
discharge air temperature setting while observing the suction
pressure. When the bypass valve starts to open, the refrigerant
line on the evaporator side of the valve will begin to feel warm
to the touch.
Figure 89. Hot gas bypass system
CAUTION
Do not touch gas liner during valve checkout. The hot gas line
can become hot enough in a short time to cause personal injury.
Combination modulation
and solenoid valves
Hot gas bypass line,
circuit #2
Hot gas bypass line,
circuit #1
To evaporator
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