Volvo V/S90 front seats retrofit/standalone.

[darxfame]

I'm also interested in how the massage is connected, via a canal or a line. But first and foremost, heating and ventilation.

[IMAY2023]

The seat ventilation and heating has nothing to do with the seat controller unit. 
It has its own LIN SLAVE module with a seperate power input about 20 AMPs.  It's LIN slave module controlled by the CCM (climate control LIN MASTER). 
Hacking a LIN is not that simple because each LIN MASTER and SLAVE responds to specific messages coming from a specific message ID.  So, you need to capture the relevant LIN messages between a CCM and Seat Heating module then send those messages to yours.