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4.9 PREPROGRAMMED SOFTWARE OVERRIDES
4.9.1 High Discharge Temperature
The control system monitors the signal provided by the compressor discharge temperature sensor. If compressor
temperature rises to the limit, the system will enter Liquid Injection Mode. In this mode the normally closed liquid
injection valve (LIV) will be opened to allow flow of refrigerant into the economizer connection to cool the compres-
sor.
4.9.2 Cargo Protect Mode
The control system will activate Cargo Protect Mode when alarms 00122 CHECK RETURN AIR SENSOR and
00123 CHECK SUPPLY AIR SENSOR activate at the same time.
• If the setpoint is in the perishable range (refer to Section 4.6.1), the unit will shutdown.
The MessageCenter will display “WARNING: NO TEMPERATURE CONTROL” when the unit is operating in Cargo
Protect Mode.
4.9.3 CSMV Control Overrides
1. Discharge Pressure Control
The control system monitors the discharge pressure. When the pressure is above the calculated maximum, the
CSMV will move toward the closed position as required to reduce the pressure.
2. Low Suction Pressure Control
The control system monitors the suction pressure. When the pressure is below the calculated minimum (-2
psig) the CSMV will move toward the open position as required to raise the pressure.
3. Compression Ratio
The microprocessor monitors compressor operating pressures and calculates a compression ratio. The
control system will open the CSMV to maintain the Maximum Compression Ratio.
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