MP-3000 Controller
115
19 Temperature Too Far From Setpoint
(Check Alarm)
• After 75 minutes of operation, supply or return air
temperature is not in-range and does not approach
setpoint within preset pull-down rate.
• Indicates:
• Ice or frost on evaporator coil
• Low refrigerant charge
• Air exchange vent open too much
• Container air leakage (doors open)
• Press S
UP/RET key to check supply and return
air sensor temperatures. Compare
temperatures to evaluate unit cooling capacity
and performance.
• Temperature difference should be 4 C to 6 C.
• Open evaporator door. Inspect coil for ice or
frost and initiate manual defrost if necessary.
• Check refrigerant charge
NOTE: This alarm can be activated if the
supply or return air temperature varies,
even if the mean temperature does
approach setpoint.
20 Defrost Time Too Long
(Check Alarm)
• Heat signal has been on for more than 90 minutes
on 60 Hz power during Defrost (120 minutes on 50
Hz power).
• Indicates:
• Low power supply voltage
• Defective heater elements
• Defective evaporator high temperature protection
switch
• Defective heat relay
• Evaporator fans running during defrost
• Evaporator sensor placed wrong
• Initiate a manual defrost and check amperage
draw and evaporator coil temperature.
Evaluate defrost performance.
• Open evaporator door and check location of
evaporator coil sensor.
NOTE: This alarm can be activated at low
voltage and very low box temperature
conditions, even under normal operating
conditions.
Alarm Codes, Descriptions and Corrective Actions (Continued)
Code Description Corrective Action
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