IM-738 Page 63
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 refrig-
erant as it passes through the evaporator high enough for
proper oil return to the compressor when cooling load condi-
tions are light.
The system consists of a solenoid valve piped in series with a
pressure regulating valve as shown in Figure 67. The solenoid
valves are factory wired to open whenever the controller calls
for the first stage of cooling. The pressure regulating valve
operates as shown in Figure 66. Since the bulb is factory
mounted in the discharge airstream where the ambient temper-
ature is about 55°F (13°C), the chart indicates that the valve is
factory set to begin opening at about 57 psig (393 kPa).
This setting can be changed by changing the pressure of the air
charge in the adjustable bulb (refer to Figure 67). To raise the
pressure setting, remove the cap on the bulb and turn the
adjustment screw clockwise. To lower the setting, turn the
screw counterclockwise. One turn is equivalent to a change of
about 1 psi (7 kPa). Do not force the adjustment beyond the
range it is designed for, as this will damage the assembly.
The regulating valve opening point can be determined by
slowly reducing the system load or reducing the required dis-
charge 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 66. Hot Gas Bypass Adjustment Range Chart
Figure 67. Hot Gas Bypass System
CAUTION
The hot gas line may become hot enough to cause injury
in a very short time, so care should be taken during valve
checkout.
T e m p e r a t u r e
° F a t B u l b L o c a t i o n
3 0
4 0
5 0
6 0 7 0
8 0 9 0
1 0 0
1 1 0
3 0
4 0
5 0
6 0
7 0
8 0
V a l v e O p e n i n g P r e s s u r e ( p s i g )
M i n i m u m
F a c t o r y S e t t i n g s
M a x i m u m
A d j u s t m e n t
R a n g e
L i q u i d
L i n e
S u c t i o n
L i n e
A d j u s t a b l e B u l b
3 / 1 6 "
H e x W r e n c h
N o t e : T h i s F i g u r e s h o w s R e f r i g e r a n t C i r c u i t # 1
H o t G a s B y p a s s
S o l e n o i d V a l v e
H o t G a s B y p a s s
L i n e
H o t G a s B y p a s s V a l v e
T h e r m o s t a t i c
E x p a n s i o n V a l v e
T o E v a p o r a t o r
D i s t r i b u t o r T u b e s
S u c t i o n L i n e
H e a d e r
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