I don’t have issues with readin or writing registers, but I think maybe I can’t write to chiller because of some restrictions. Also I have a MCM-A00N controller for DVM Chiller. Can be this controller the issue.
Most of modbus interfaces have no security or security based on sequence of operations (write “auth” register, then write desired register). What I am trying to say is - a basic fact that you configured reading side does not make openHAB automatically assume anything for writing. In order to write you need to add couple more options which I mentioned above.
Regardless of options, you can also turn debug logs for modbus binding to see if it refuses write attempts or attempt to perform them. Anyhow, if you have a working BMS which is already controls that chiller, might be overwritten by BMS within some period of time.
I never got back to this, but allow me to do an update for the sake of future reference.
Later I did tried with a proper cable, connecting the USB stick directly to the external AC unit and the results were the same.
So I can only asume that there might be a problem either with the USB stick itself, not being able to read properly the values, or with the modbus card on the AC units.
And that’s it. I can send write but I can never read.