Danfoss E39

What does Danfoss E39 mean?

E39 indicates a fault on the signal from the P0 input on a Danfoss EKC controller, meaning the evaporating-pressure transmitter is not delivering a valid reading. On a superheat controller P0 is essential for calculating superheat, so this fault disrupts regulation. The alarm relay activates at high priority and the front-panel LEDs flash to indicate the error.

Symptoms

• Display shows E39 when the alarm is recalled.
• P0 (evaporating pressure) reading is missing or out of range.
• Front-panel LEDs flash to indicate the regulation error.
• Superheat calculation that relies on P0 becomes unreliable.

Common causes

• Pressure transmitter on the P0 input has failed.
• Broken or disconnected transmitter signal wiring.
• Transmitter output outside the configured working range.
• Loss of supply power to the pressure transmitter.

Diagnostic steps

1. 01

   Recall the alarm code

   Press the top button to display E39, then press again to cancel the active alarm.

2. 02

   Inspect the P0 transmitter wiring

   Power down and check the P0 transmitter signal wires and power supply for breaks or loose terminals.

3. 03

   Confirm the transmitter range

   Verify the controller's pressure-range parameters match the installed P0 transmitter so its signal falls within the valid band.

4. 04

   Test or replace the transmitter

   Measure the transmitter signal; if absent or incorrect, fit a replacement P0 pressure transmitter of the correct type.

When to call a professional

Because P0 drives the superheat calculation that protects the compressor, E39 should be corrected promptly. A refrigeration technician should test the low-side pressure transmitter, confirm the controller's range settings, and replace the transmitter where required. The work can involve connecting gauges and handling refrigerant, which requires certification. Untrained staff should not attempt pressure-circuit diagnosis or transmitter replacement.