42 Component Operation and Maintenance
6.4.5 Hot Gas Bypass Valve
Operation
The hot gas bypass is inserted between the compressor discharge line and the leaving side of the
expansion valve through the side outlet distributor. The system, with normal operation when the
evaporator is under full load, will maintain enough pressure on the leaving side of the hot gas valve to
keep the valve port closed.
If the load on the evaporator decreases, the evaporator will get colder. When the coil is too cold, the
internal pressure in the evaporator drops and allows the hot gas bypass valve to open. Hot gas then
mixes with the liquid coolant on the discharge side of the expansion valve raising the temperature
and pressure in the evaporator. The net result is a reduction in the cooling capacity of the unit to
match the load.
To aid in lubricating the compressor, the hot gas bypass solenoid is delayed for 30 seconds on the initial
call for cooling and de-energized for 30 seconds during every 60 minutes of continuous operation.
Adjustment
Upon deciding what evaporator temperature is desired, the following procedure should be used to
adjust the hot gas bypass valve:
1. Install the suction and discharge pressure gauge.
2. Adjust the temperature setpoint to call for cooling so that the refrigeration compressor will run.
3. Remove the protective cap from the valve.
4. Insert an adjustment tool into the setting screw, and turn CLOCKWISE if a higher evaporator
temperature is required.
5. After obtaining the suction pressure required, reinstall the cap tightly making sure there are no
leaks.
6. Let the evaporator operate for approximately 10 to 15 minutes to make sure the suction pressure
is within the range desired.
7. There will be a fluctuation of approximately 3 to 6 PSIG (21 to 41 kPa) on the evaporator due to
the differential on the hot gas bypass.
8. Return the temperature setpoint to desired number.
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