Danfoss AKC Controller Fault Codes - Quick Reference
Danfoss AKC controllers (AKC 15, 22, 24, 55, 114, and the newer AK-CC series) manage refrigerated display cases, walk-in coolers, and rack systems. Alarms appear on the controller display and via the Danfoss AKM or ADAP-KOOL network.
| Alarm / Code | Meaning | Quick Fix |
|---|---|---|
| A1 - Temperature High | Case temperature above alarm setpoint | Check defrost, door seals, fans |
| A2 - Temperature Low | Case temp below low alarm setpoint | Check thermostat/thermistor |
| A3 - Defrost Timeout | Defrost exceeded maximum time | Check defrost heater and termination |
| A4 - Sensor Fault | Temperature sensor open or shorted | Check sensor wiring |
| A5 - Defrost Sensor Fault | Defrost termination sensor fault | Check termination sensor |
| A6 - Door Switch Alarm | Door open too long | Check door and switch |
| A7 - Communication Fault | Network communication lost | Check LonWorks/RS-485 wiring |
| A8 - Air Sensor Fault | Air inlet or outlet sensor fault | Check sensor |
| A9 - Power Fail | Supply power was interrupted | Normal after power outage |
| A10 - Controller Fault | Internal controller error | Replace controller |
Most Common Faults
A1 - Temperature High
Most common alarm on AKC controllers. First check if a recent defrost cycle completed normally. Ice buildup from a failed defrost blocks evaporator airflow and causes temperature rise within hours. Also check door gaskets and night curtains. If defrost is fine, suspect evaporator fan motor failure.
A3 - Defrost Timeout
AKC controllers terminate defrost on either temperature (termination sensor reaches setpoint) or time (maximum defrost duration). A timeout means the coil didn’t reach the termination setpoint within the time limit. Check the defrost heater with an ohmmeter - open heater elements are common on aging equipment. Also check the safety thermostat.
A4 - Sensor Fault
Danfoss uses NTC (10K or 20K at 25°C depending on model) temperature sensors. A disconnected or failed sensor causes A4. Test the sensor resistance at the controller terminal. Danfoss AK sensors have a standard curve - any value below 200 Ohms or above 500K Ohms indicates failure.
A7 - Communication Fault
AKC controllers on LonWorks or RS-485 networks alarm on communication loss. Check LonWorks cable polarity and termination - LonWorks requires twisted-pair with proper termination at each end. RS-485 requires a 120-ohm terminator at each trunk end and correct addressing.
Parts Often Needed
| Part | Notes |
|---|---|
| AKC temperature sensor (NTC) | Replace on A4/A5 fault |
| Defrost heater element | Replace on A3 timeout |
| Defrost safety thermostat | Replace on A3 timeout |
| Evaporator fan motor | Replace on temperature alarm |
| AKC controller | Replace on A10 fault |
Related Resources
- Browse all VFD fault codes — ABB, Allen-Bradley, Yaskawa, Siemens drives and more
- Browse all Danfoss error codes — comprehensive reference
Need Replacement Parts?
Finding the right replacement parts for your equipment is critical to getting it running again. Check current prices on Amazon — prices and availability change frequently.
When to Call a Pro
Danfoss ADAP-KOOL network configuration and AKM system management require Danfoss-trained refrigeration controls technicians. A misconfigured AKC defrost schedule can cause food safety violations.