McQuay SEASONCON ALP-037A, Manual, Page: 42 / 43

HOT GAS BYPASS (OPTIONAL)
Hot gas bypass is a system for maintaining evaporator pres-
sure at or above a minimum value. The purpose for doing
this 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. Hot
gas bypass kits are described on page 9.
The solenoid valve should be wired to open whenever
the unit thermostat calls for the first stage of cooling (see
Figure 11). The pressure regulating valve that McQuay
offers is factory set to begin opening at 58 PSIG (32F for
R-22)
when the air charged bulb is in an 8OF ambient
temperature. The bulb can be mounted anywhere as long as
it senses a fairly constant temperature at various load
conditions. The compressor suction line is one such
mounting location. It is generally in the 50F to 60F range.
The chart on page 50 indicates that when the bulb is
sensing 50F to 60F temperatures, the valve will begin
opening at 54 to 56 PSIG. This setting can be changed as
indicated above, by changing the pressure of the air charge
in the adjustable bulb. To raise the pressure setting, remove
the cap on the bulb and turn the adjustment screw clock-
wise. To lower the setting, turn the screw counterclockwise.
Do not force the adjustment beyond the range it is designed
for, as this will damage the adjustment assembly.
The regulating valve opening point can be determined by
slowly reducing the system load while observing the suction
pressure. When the bypass valve starts to open, the refrig-
erant line on the evaporator side of the valve will begin to
feel warm to the touch.
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.
On installations where the condensing unit is remote
from the evaporator, it is recommended that the hot gas
bypass valve be mounted near the condensing unit to
minimize the amount of refrigerant that will condense in
the hot gas line during periods when hot gas bypass is not
required.
HOT GAS BYPASS PIPING DIAGRAM
HOT GAS BYPASS ADJUSTMENT RANGE
Hot Gas Bypass
Solenoid Valve
Line
Inlet After
in ALP Unit
Bypass Valve Expansion Valve
(On DX Coils with
Distributors, use
Sporlan Auxiliary
Connector
or Equivalent)
R E
M
OTE A D J U S T
M
ENT RANGE
30
30 70 90 100
A T B U L B L O C A T I O N
PAGE 42