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5.9 Compressor management
ems controllers manage the compressor tomaintain the product temperature betweenthe set point (SP)
temperature and the set point (SP) plus differential (dIF) temperature in the ready mode or between the saving set
point (SSP) temperature and the saving set point (SSP) plus the saving differential (Sd) temperature in the saving
mode.
To ensure that the pressures within the refrigeration system have time to equalize during compressor off-cycles,
the compressor rest time (rt) defines the minimum time that the compressor can be switched off. Compressor
manufacturers usually recommend a minimum compressor rest time. The compressor rest time (rt)helps to avoid
the following:
• Passing peak current through the windings of the compressor motor
• Switching off the refrigeration system on the thermal overload protection
• Short-cycling the refrigeration system
However, if ready mode and saving mode differential temperatures are too small or if the compressor rest time (rt)is
too short, the ems controller cycles the compressor on the compressor rest time (rt) as the compressor rest time (rt)
over-rides the differential temperatures.
If the compressor runs continuously for too long without reaching the set point (SP) temperature, a refrigeration
system failure (rSF) alarm activates alerting to possible problems with the refrigeration system.
ems controllers can monitor the refrigeration system temperature using a condenser sensor. Monitoring the
refrigeration system temperature can help detect problems, such as a blocked condenser. If the temperature
measured on the condenser sensor reaches the condenser high temperature (Ct), the ems controller disables the
compressor and activates the (Ht) alarm. The condenser high temperature (Ct) is set by measuring the refrigeration
system temperature when the condenser is 75% blocked.
ems controllers manage the failure of at emperature sensor as follows:
• Appliance sensor failures indicated by PF1 alarms, ems controllers stop running the compressor and then wait
60 seconds before rebooting (switch off and then switch on). If the fault continues, the ems controller repeats
and continues the cycle
• Condenser sensor failures indicatedby PF2 alarms, ems controllers continue running the compressor. ems
controllers alternate the display between PF2 and the appliance sensor temperature
• PF2 alarms may also indicate a problem with the gas cooler high temperature sensor when the cooler is a CO2
(R744) version. An ems55advanced CO2 controller will alternate between PF2 and the gas cooler temperature
sensor temperature.
• For evaporator failures indicated by PF3 alarms, ems controllers continue running the compressor. ems
controllers alternate the display between PF3 and the appliance sensor temperature
Note
Ht alarms do not apply to CO2 coolers
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