Danfoss A15

What does Danfoss A15 mean?

On the Danfoss ERC 21X controller, A15 is a DI alarm, meaning an external alarm has been received on a digital input. An external device or switch wired to the controller's digital input has signalled a fault condition, and the controller relays it as A15. The display alternates between the air temperature and the active alarm codes, and the alarm relay is activated.

Symptoms

• Display alternates between air temperature and the code A15.
• An external device or switch has changed the digital input state.
• Alarm relay is activated.
• The specific external fault depends on what is wired to the input.

Common causes

• An external alarm device (such as a pressure or safety switch) has tripped.
• Digital input polarity (P73/P74) set opposite to the connected contact.
• Wiring fault on the digital input creating a false alarm.
• The monitored external condition is genuinely present.

Diagnostic steps

1. 01

   Identify the input source

   Confirm A15 and determine which external device or switch is connected to the controller's digital input.

2. 02

   Check the external device

   Inspect the device that drives the input (for example a pressure or safety switch) to see whether its fault condition is real.

3. 03

   Verify input polarity

   Confirm the digital input polarity parameter (P73 or P74) matches the connected contact type, normally open or normally closed.

4. 04

   Confirm the alarm clears

   Once the external condition is cleared and the wiring is correct, verify A15 disappears.

When to call a professional

Because A15 reflects whatever external device is wired to the digital input, diagnosing it requires knowing the installation. A refrigeration technician familiar with the system can identify the connected safety or pressure device, confirm the input polarity settings, and decide whether the external fault is genuine. If the alarm is tied to a safety interlock, do not bypass it; have trained staff resolve the underlying condition first.