20 Defrost Time Too Long (Check Alarm)

Thermo King Alarm Code

Description	Corrective Action
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.