Danfoss A99 Error Code

What does Danfoss A99 mean?

On the Danfoss ERC 21X controller, A99 is a high-voltage alarm meaning the supply voltage is too high. The controller monitors the incoming supply to protect the compressor, and A99 warns that the voltage has risen above the safe range. The display alternates between the air temperature and the active alarm codes, and the alarm relay is activated to flag the protection event.

Symptoms

• Display alternates between air temperature and the code A99.
• Compressor operation may be inhibited for protection.
• Alarm relay is activated.
• The condition correlates with a measured supply above the normal range.

Common causes

• Mains supply voltage above the appliance's rated range.
• Unstable or surging incoming power.
• Incorrect supply connection or wrong voltage tap.
• Site power-quality problem upstream of the unit.

Ask the AskWhiz AI about Danfoss A99

AskWhiz

online

Hi — I'm the Refrigeration demo. Ask me anything in this domain.

What causes Danfoss A99?Step-by-step fix for Danfoss A99?Is Danfoss A99 safe to ignore?

MessageHelp me troubleshoot Danfoss A99

Diagnostic steps

1. Read the alarm

   Confirm A99 on the display to identify the high-voltage protection event.

2. Measure the supply voltage

   Use a meter to check the incoming supply against the appliance's rated voltage (115 V AC / 230 V AC).

3. Check the supply connection

   Confirm the unit is wired to the correct supply and that no loose neutral or wrong tap is raising the voltage.

4. Confirm recovery

   Once the supply returns to the normal range, verify A99 clears and the compressor resumes protected operation.

When to call a professional

A high-voltage alarm points to a mains supply problem rather than a fault inside the appliance. A qualified electrician should measure the supply, check for an open neutral or wiring error, and confirm the site power is within tolerance. Operating sensitive compressor electronics on an out-of-range supply risks damage, so the power fault should be corrected by a competent person before relying on the unit.