Danfoss AA1

What does Danfoss AA1 mean?

On the Danfoss ERC 21X controller, AA1 is a low-voltage alarm meaning the supply voltage is too low. The controller monitors the incoming supply to protect the compressor, and AA1 warns that the voltage has fallen below the safe range, where a compressor could draw excessive current. 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 AA1.
• Compressor operation may be inhibited for protection.
• Alarm relay is activated.
• The condition correlates with a measured supply below the normal range.

Common causes

• Mains supply voltage below the appliance's rated range.
• Voltage drop on a long or undersized supply cable.
• Overloaded circuit or weak site supply.
• Loose connection adding resistance in the supply path.

Diagnostic steps

1. 01

   Read the alarm

   Confirm AA1 on the display to identify the low-voltage protection event.

2. 02

   Measure the supply voltage

   Check the incoming supply at the appliance against its rated voltage (115 V AC / 230 V AC).

3. 03

   Inspect the supply path

   Look for loose terminals, undersized cable, or an overloaded circuit causing the voltage to sag under load.

4. 04

   Confirm recovery

   Once the supply returns to the normal range, verify AA1 clears and the compressor resumes protected operation.

When to call a professional

A low-voltage alarm indicates a supply problem that can damage the compressor through under-voltage running. A qualified electrician should measure the supply under load, check for voltage drop on the feed, and correct loose connections or undersized wiring. Because the fault lies in the building's electrical supply rather than the appliance, it should be diagnosed and repaired by a competent electrical person.