Thermostatic Expansion Valve; Hot Gas Bypass Valve-Not Available On Digital Scroll Units - Emerson Liebert Challenger iCOM 3000 Operation & Maintenance Manual

3.4.4

Thermostatic Expansion Valve

Operation
The thermostatic expansion valve performs one function. It keeps the evaporator supplied with
enough refrigerant to satisfy load conditions. It does not effect compressor operation.
Proper valve operation can be determined by measuring superheat. If too little refrigerant is being fed
to the evaporator, the superheat will be high; if too much refrigerant is being supplied, the superheat
will be low. The correct superheat setting is between 10 and 15°F (5.6 and 8.3°C).
Adjustment
To adjust the superheat setting:
1. Remove the valve cap at the bottom of the valve.
2. Turn the adjusting stem counterclockwise to lower the superheat.
3. Turn the adjusting stem clockwise to increase the superheat.
NOTE
Make no more than one turn of the stem at a time. As long as 30 minutes may be required
for the new balance to take place.
3.4.5 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
initial call for cooling and de-energized for 30 seconds during every 60 minutes of continuous
operation.
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,
www.liebert.com
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.
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Liebert ® Challenger 3000
Component Operation and Maintenance
12