Everlasting dFd

What does Everlasting dFd mean?

dFd is the defrost-timeout alarm. When enabled (parameter d11), the controller raises it if a defrost cycle runs to its maximum allotted time without the evaporator reaching the temperature that would normally end defrost. It indicates the coil did not clear within the expected window, so defrost terminated on time rather than on temperature and ice may remain on the evaporator.

Symptoms

• dFd shown on the controller display with the alarm LED active
• Defrost ending on maximum time rather than on temperature
• Visible ice or frost remaining on the evaporator after defrost
• Reduced airflow or cooling efficiency from a partly iced coil

Common causes

• Heavy ice build-up that the defrost cycle cannot fully clear in time
• Defrost heater fault or weak defrost performance
• Evaporator probe issue affecting defrost termination
• Defrost duration parameters set too short for conditions

Diagnostic steps

1. 01

   Confirm the alarm

   Read dFd on the display; it indicates the last defrost ran out of time without completing on temperature.

2. 02

   Inspect the evaporator

   Check the coil for heavy ice or frost that the standard defrost cycle could not clear within its maximum time.

3. 03

   Run a manual defrost

   Initiate a defrost from the keypad and watch whether the coil clears, which helps distinguish heavy icing from a defrost-heater problem.

4. 04

   Check related faults

   Note whether an evaporator probe fault (Pr2) is also present, since that forces defrost onto a safety timer and can lead to incomplete defrosts.

5. 05

   Escalate heater faults

   If the coil will not clear and a defrost-heater fault is suspected, contact technical support for repair.

When to call a professional

Contact technical support if dFd recurs and the coil will not fully defrost, since the manual associates persistent icing with a defrost-heater fault that is reserved for authorized service. Diagnosing and replacing defrost heating elements or adjusting defrost parameters falls under extraordinary maintenance, which the manual restricts to specialist personnel, so do not attempt heater repairs yourself.