Eberspächer Heater Blower Relay for Volvo 855

I purchased a Volvo 855 TDI from 1996 with a built-in Eberspächer Hydronic (?) auxiliary heater. The TP48 remote control works. The heater starts and heats the engine coolant well, but the interior fan does not work, meaning the interior is not heated. I believe the heater was retrofitted and not originally installed. The fuses are intact, and the heater fan works perfectly in the "normal" heating system. Allegedly, the retrofit kits have a relay for controlling the heater fan. In the simplest case, the problem might be there. Unfortunately, I have no idea what the relay looks like or where to find it. http://members.aon.at/msemrad/A160/Bausatz.jpg shows a newer installation kit. The only thing that looks like a relay there is a small black box on the right. Can someone help me identify the relay? Where should I look, and what size is it?

I accidentally posted my question in the wrong forum, sorry.