Hello mortenx;

I have not worked with Carel Boss controllers, but their website states that they support  both Modbus TCP and Modbus RTU connections. The Sentron PAC2200 offers both formats of Modbus also, which have you chosen for this project?

The video link below shows how to use Siemens TIA Portal software (for a S7-1200 controller) to connect to a PAC2200 over Modbus TCP, if that can help you with the setup of the SENTRON unit side.

 To configure the PAC2200 for Modbu communications you need the powerconfig editor:

- Parameterizing PAC2200 with SENTRON powerconfig

https://support.industry.siemens.com/cs/ww/en/view/109746835/146457625099

- Download of Powerconfig software v3.19

https://support.industry.siemens.com/cs/ww/en/view/63452759

And in the SENTRON PAC2200 manual you will find a list of available  registers, with ther Modbus offsets:

-  PAC2200 Modbus measured variables with the function codes 0x03 and 0x04

https://support.industry.siemens.com/cs/ww/en/view/109746835/146507142411

Hope this helps,

Daniel Chartier