Danfoss E27

What does Danfoss E27 mean?

On the Danfoss ERC 21X controller, E27 means the defrost (S5 evaporator) sensor is defective or its electrical connection is lost. The controller uses this sensor to terminate defrost on temperature, so when it fails defrost control reverts to timed operation and evaporator monitoring is impaired. The display alternates between the air temperature and the active alarm code while the alarm relay is activated.

Symptoms

• Display alternates between air temperature and the code E27.
• Evaporator (S5) temperature reading is missing or faulted.
• Defrost may end on time rather than on temperature.
• Alarm relay is activated.

Common causes

• Evaporator (S5) sensor is defective.
• Electrical connection to the evaporator sensor is lost or broken.
• Sensor cable damaged by ice, frost cycling, or abrasion.
• Loose or corroded terminal at the sensor input.

Diagnostic steps

1. 01

   Confirm the alarm source

   Read the display alternating between air temperature and E27 to identify the evaporator sensor as the fault.

2. 02

   Inspect the evaporator sensor wiring

   Power down and check the S5 cable and terminals, paying attention to areas exposed to frost and defrost heat.

3. 03

   Measure the sensor

   Disconnect S5 and measure its resistance against the fitted sensor type; an open or shorted value confirms a failed sensor.

4. 04

   Replace the evaporator sensor

   Fit a new sensor of the correct type, secure it on the evaporator coil as before, and confirm E27 clears on power-up.

When to call a professional

The evaporator sensor sits on the coil where access can be difficult and ice can hide cable damage. If E27 returns after replacement, a refrigeration technician should check the defrost configuration and sensor placement. Incorrect defrost termination leads to coil icing and poor cooling, so trained verification of the sensor type and mounting protects efficient, reliable operation of the case or cold room.