Danfoss AK-RC 305W-SD

Name: Danfoss AK-RC 305W-SD Modbus register map
Creator: ModbusCloud
Published: 2026-11-01T13:42:47.171352+00:00

Cold room controller for walk-in coolers and freezers: temperatures, relays, defrost and alarms.

The Danfoss AK-RC 305W-SD is a temperature controller in a wall box that runs the compressor, defrost, evaporator fans and light of a walk-in cooler or freezer. This Modbus RTU template reads probe temperatures, relay states and alarms, and lets you write the setpoint, start a defrost and switch standby and light from ModbusCloud.

Protocol: Modbus RTU
Connection: RS485, 19200 baud
Registers: 112, read and write

Brand: Danfoss
Key readings: Room temperature S1 · Evaporator temperature S2 · Effective setpoint · Cooling relay · Defrost state · Alarms
Available commands: Setpoint · Defrost start and stop · Standby · Light · Alarm limits
Compatible models: AK-RC 305W-SD (080Z5003)
Last updated: 1 November 2026

Registers (112)

112 read, 76 write

Name	Unit	Access
Probe S1 Temperature	°C	Read
Probe S2 Temperature	°C	Read
Probe S3 Temperature	°C	Read
Effective Setpoint	°C	Read
Cooling Relay State		Read
Defrost Relay State		Read
Fan Relay State		Read
Defrost State		Read
Standby State		Read
Digital Input 1 State		Read
Digital Input 2 State		Read
Light State		Read
AUX1 Remote State		Read
AUX2 Remote State		Read
Setpoint Change State		Read
Continuous Cycle State		Read
Mute State		Read
Alarm Max S1		Read
Alarm Min S1		Read
Alarm Door Open		Read
Alarm External		Read
Alarm Severe External		Read
Probe S1 Error		Read
Probe S2 Error		Read
Probe S3 Error		Read
Alarm Moisture S2		Read
Alarm Moisture S3		Read
Alarm HACCP		Read
Alert Defrost Time		Read
Alert Pump Down Pd		Read
Alert Pump Down LP		Read
Alert Power Fail HACCP		Read
Alert HACCP		Read
Alarm SD 16		Read
Switch Standby		Read and write
Switch Setpoint Change		Read and write
Switch Continuous Cycle		Read and write
Switch Light		Read and write
Turn On Mute		Read and write
Switch AUX1		Read and write
Switch AUX2		Read and write
Turn On Defrost		Read and write
Turn Off Defrost		Read and write
Setpoint	°C	Read and write
Regulation Mode		Read and write
Probe 1 Calibration	K	Read and write
Probe 1 Differential	K	Read and write
Setpoint Upper Limit	°C	Read and write
Setpoint Lower Limit	°C	Read and write
Delay Type		Read and write
Delay Time		Read and write
Cooling On Probe Failure		Read and write
Cooling Time On On Failure		Read and write
Cooling Time Off On Failure		Read and write
Max Duration Continuous Cycle		Read and write
Setpoint Variation Continuous Cycle	K	Read and write
Setpoint Variation	K	Read and write
Max Time On Pump Down		Read and write
Max Time Pump Down		Read and write
Probe Displayed		Read and write
Stop Fan With Cooling		Read and write
Fan On Delay		Read and write
Fan Stop Delay		Read and write
S1 S3 Balance		Read and write
S3 Calibration	K	Read and write
Defrost Frequency		Read and write
Defrost Duration		Read and write
Defrost Message		Read and write
Defrost Message Duration		Read and write
End Defrost Temperature	°C	Read and write
Defrost At Start Up		Read and write
Start Up Defrost Delay		Read and write
Defrost Type		Read and write
Time Between Defrosts Mode		Read and write
Drip Time		Read and write
Fan Stop Temperature	°C	Read and write
Probe 2 Differential	K	Read and write
Stop Fan With Compressor		Read and write
Fans During Defrost		Read and write
Fan Delay After Defrost		Read and write
Fan Stop Evaporator Temperature	°C	Read and write
Fan On Cycle		Read and write
Fan Off Cycle		Read and write
Alarm Setup		Read and write
Max Alarm S1	°C	Read and write
Min Alarm S1	°C	Read and write
Alarm Start Up Delay		Read and write
Alarm Delay After Defrost		Read and write
Temperature Alarm Delay		Read and write
External Alarm Delay		Read and write
External Alarm Off Delay		Read and write
Defrost Warning		Read and write
Alarm Relay Polarity		Read and write
Alarm Differential	K	Read and write
Open Door Alarm Delay		Read and write
Start Up Delay		Read and write
Light Time		Read and write
Password Function		Read and write
Password		Read and write
Acoustic Alarm		Read and write
Work Units		Read and write
Connected Probes		Read and write
Digital Input 1 Setup		Read and write
Digital Input 1 Polarity		Read and write
Digital Input 2 Setup		Read and write
Digital Input 2 Polarity		Read and write
AUX1 Setup		Read and write
AUX2 Setup		Read and write
HACCP Temperature	°C	Read and write
HACCP Delay		Read and write
Start Wizard		Read
Pump Down		Read

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Use cases

Show room temperature, evaporator temperature and relay states of every cold room on one dashboard.
Get an email when the high or low temperature alarm, door alarm or a probe error turns on.
Keep a year of cold room temperature history as a record for food safety checks.
Start a manual defrost from ModbusCloud when the evaporator ices up.
Raise or lower the setpoint remotely when the room changes from cooler to freezer use.

Installation

Wire the RS485 terminals of the AK-RC 305W-SD to the RS485 port of the ModbusCloud Gateway, with a 120 ohm resistor at both ends of the bus.
Check the address and serial settings of the controller; this template assumes 19200 baud, 8E1 and address 1.
In ModbusCloud, add a Modbus device (RTU) with those settings and import this template.
Check that probe S1 shows the room temperature and that the cooling relay state follows the display.
Add alarm rules on the alarm registers you want to follow, such as max and min alarm S1 and door open.

Things to watch for

The controller does not answer on the bus. What should I check?

The serial settings are not in the Modbus list, so check them on the controller first. Try 19200 baud, even parity, 1 stop bit and address 1. Swap A and B if nothing answers, and make sure the bus has a 120 ohm termination at both ends.

Why does a probe show -327.67?

That is the raw value -32767, which the controller sends when a probe has no valid reading. Check the probe and its wiring; the matching probe error register will be on as well.

Why are temperatures a hundred times too high?

Temperatures are sent in hundredths of a degree, so 450 means 4.50. The template applies that scale. If the controller is set to Fahrenheit, the values are in °F.

How do I start a defrost or change the setpoint safely?

Write 1 to Turn On Defrost to start one and to Turn Off Defrost to end it; Defrost State shows the result. Write the setpoint in degrees within the upper and lower setpoint limits. Agree remote changes with whoever is responsible for the cold room.

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