User Manual

Table Of Contents

Component Operation and Maintenance

7.4.5 Hot Gas Bypass Valve—Not Available on Digital Scroll Units

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 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 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.

7.4.6 Air 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.

NOTE

These procedures are not applicable to condensing units. For condensing unit information,

refer to Liebert’s condensing unit manual, SL-10059, available at the Liebert Web site,