Randell E04

What does Randell E04 mean?

On a Randell prep table with the Danfoss controller, E04 is the S4 Sensor Failure alarm. S4 is one of the controller's temperature sensors (thermistors). E04 indicates the controller cannot read a valid value from S4 because the sensor has failed, drifted out of range, or lost its connection, affecting the function that sensor monitors.

Symptoms

• Display shows E04 with the alarm LED lit
• Temperature control tied to the S4 sensor is affected
• Displayed temperature may be missing or incorrect
• Cooling or defrost behavior may be abnormal

Common causes

• Failed or out-of-range S4 thermistor
• Disconnected or loose S4 sensor connector at the controller
• Damaged sensor wiring
• Controller input fault

Diagnostic steps

1. 01

   Confirm the alarm

   Verify the Danfoss display reads E04, the S4 Sensor Failure alarm.

2. 02

   Disconnect power before inspecting

   Ensure the unit is disconnected from its power source before checking the sensor or wiring, per the manual.

3. 03

   Inspect the S4 sensor connection

   Check that the S4 thermistor is connected at the controller and that its wiring is not damaged or loose.

4. 04

   Verify cabinet temperature

   Compare the displayed temperature against the set point to judge whether the unit is still holding safe temperature.

5. 05

   Contact service

   The Danfoss table directs contacting service for a sensor failure; call 888-994-7636 to test or replace the S4 thermistor.

When to call a professional

The Danfoss code table directs contacting service for an S4 sensor failure. Determining which thermistor has failed and replacing it with the correct OEM part is service-technician work, and the manual requires factory-authorized service with OEM parts on these R290 units. Call a Randell Authorized Service Agent at 888-994-7636 if E04 does not clear after checking the connection.