Component Operation and Maintenance
7.4.5Hot Gas Bypass
Operation—Self-Contained Units
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 ini- tial call for cooling and
NOTE
These procedures are not applicable to condensing units. For condensing unit information, refer to Liebert’s condensing unit manual,
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 TOP adjusting nut from the valve.
4.Insert an Allen wrench in the brass hole at top of the valve in adjusting port, 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 desired range.
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.
7.4.6Air Cooled Condenser
Restricted airflow through the condenser coil will reduce the operating efficiency of the unit and can result in high compressor head pressure and loss of cooling.
Clean the condenser coil of all debris that will inhibit air flow. This can be done with compressed air or commercial coil cleaner. Check for bent or damaged coil fins and repair as necessary. In winter, do not permit snow to accumulate around the sides or underneath the condenser.
Check all refrigerant lines and capillaries for vibration isolation. Support as necessary. Visually inspect all refrigerant lines for signs of oil leaks.
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