Domekt Komfovent C4 Plus Modbus Registers

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Domekt Komfovent C4 is a AHU (Air Handling Unit) for use in a HVAC system. The C4 is an older standard use from approx. 2011 to 2016.

Connection

Connect the unit to a computer using the provided RS485/ModBus cable extruding from the top. There is no need to add 820 Ohm 5V pull-up/gnd pull-down or 120 Ohm termination. It works fine as is.

The pin-out is as the following:

RJ-45 flat cable Wire color Function
Pin 1 Color Not used
Pin 2 Color Not used
Pin 3 Red +24VDC
Pin 4 Yellow RS485 A+
Pin 5 Green RS485 B-
Pin 6 White Gnd
Pin 7 Color Not used
Pin 8 Color Not used

Modbus settings

To establish a working connection, it's important to match the following connection parameters. A single wrong setting will make the connection not work at all.

Bits per second/baudrate 19200
Data bits/word length 8
Parity Even
Stop bits 1

It is also important to use the correct Modbus ID. It's the identifier on the bus and has to be correct in order for communication to happen with the AHU.

The C4 unit has a different Modbus ID than later models, so make sure to double check. Either of the following will work with only one unit on the Modbus line.

Modbus ID 20 (specific identification address) 254 (common identification address)

Register list

The C4 unit uses the following Modbus data register functions to read and write data.

A CR2032 battery keeps the registers concurrent when the unit is unplugged, ex. the time and date.

Read data: Function code 03 Operation status, temperatures, fans speed, and etc.
Write data single register: Function code 06 Turn on/off unit, set temperature, change auto/manual mode
Write data multiple registers: Function code 16 Set values with decimals/floating integers

Controller registers available on the C4 unit.

General settings and status

Modbus register Type Access Range Description Data values
1000 Read/write Integer 0..1 C4 Start/stop unit 1-Start, 0-Stop
1001 Read/write Integer 0..1 Season, heating enabled or prohibited 1-Winter, 0-Summer
1002 Read/write 2x Char 0x0000..0x2359 Time, hh:mm Ex. 8:05 => 0x0805
1003 Read/write Integer 1-7 Day of the week 1-Mon, 2-Tue, 3-Wed, 4-Thu, 5-Fri, 6-Sat, 7-Sun
1004 Read/write 2x Char 0x0101..0x1231 Month-day date Ex. 9th May => 0x0509
1005 Read/write Integer 1900-2100 Year date Ex. 2023
1006 Read/write Integer 1..100 Modbus ID, default 20 Ex. 20
1007 Read Integer - Alarm status (warnings) 14-Service, 13-Heater off, 11-Rotor stop
1008 Read Binary b0-b7, 0..1 Alarm status (stop flags) b1-Supply sensor B1,
b2-Heater overheating,
b3-Water temp. low,
b4-Rotor stop,
b5-Frost possibility,
b6-Air temp. high,
b7-Air temp. low
1009 Read Integer 3..28 Alarm status (stop code) 3-Rotor stop,
4-Heater overheating,
9-Supply sensor B1,
19-Air temp. low,
20-Air temp. high,
27-Water temp. low,
28-Frost possibility
1010 Read Integer 0..100 Recuperation level (heat exchanger) 0 to 100%
1011 Read Integer 0..100 Electric heater level (heating element) 0 to 100%
1012 Read Integer 0..100 Water heating level (external) 0 to 100%
1013 Read Integer 0..100 Water cooling level (external) 0 to 100%


Ventilation settings and status

Modbus register Type Access Range Description Data values
1100 Read/write Integer 1..3 Ventilation level (manual mode) 1-Low fan speed,
2-Normal fan speed (recommended),
3-High fan speed
1101 Read Integer 0..4 Ventilation level (current operation) 0-Off, 1-Low fan speed,
2-Normal fan speed,
3-High fan speed,
4-Override mode
1102 Read/write Integer 0..1 Mode (Auto/Manual) 0-Manual (set fan speed), 1-Auto (schedule)
1103 Read/write Integer 20..100 / 0 Intake ventilation intensity level 1 (EC-type fan) 20 to 100% (EC-fan only)
1104 Read/write Integer 20..100 / 0..2 Intake ventilation intensity level 2 (EC-type fan / AC-type fan) 20 to 100% (EC-fan), 0 to 2 (AC-fan)
1105 Read/write Integer 20..100 / 0 Intake ventilation intensity level 3 (EC-type fan) 20 to 100% (EC-fan only)
1106 Read/write Integer 20..100 / 0 Intake ventilation intensity level 4 (EC-type fan) 20 to 100% (EC-fan only)
1107 Read/write Integer 20..100 / 0 Exhaust ventilation intensity level 1 (EC-type fan) 20 to 100% (EC-fan only)
1108 Read/write Integer 20..100 / 0..2 Exhaust ventilation intensity level 2 (EC-type fan / AC-type fan) 20 to 100% (EC-fan), 0 to 2 (AC-fan)
1109 Read/write Integer 20..100 / 0 Exhaust ventilation intensity level 3 (EC-type fan) 20 to 100% (EC-fan only)
1110 Read/write Integer 20..100 / 0 Exhaust ventilation intensity level 4 (EC-type fan) 20 to 100% (EC-fan only)
1111 Read/write Integer 0..1 Override/"OVR"-mode 0-Disable, 1-Enable
1112 Read/write Integer 1..90 Override mode timer 1 to 90 minutes
1113 Read Integer 0..90 Override mode timer (current count down) 0 to 90 minutes
1114 Read Binary 0..1 AHU / Air Handling Unit fans status 0-Stopped, 1-Operating
1115 Read Integer 0..100 Supply fan level (current level) 0 to 100%
1116 Read Integer 0..100 Exhaust fan level (current level) 0 to 100%