Steve,
and whoever is interested or have a similar problem:

Thanks again. You were right, it was the power stage unit (this part Volvo service call "Transistor" - sic!) that caused the whole problem.
Volvo charges 111.00 CAN$ for the part +15% tax for it. Since this is kind of unreasonable price for the piece of heat radiating block with 2 transistors and 1 resistor (I bet that is produced in China for 5$ - 10$ wholesale), I have decided to play a bit with it.

Luckily, I was able to narrow the problem to small transistor that controls the other big, power one. 4 bucks later it was working fine.

Now I am going with pleasure after incompetent Volvo service that charged me about 120$ for the wrong diagnose and also recommended to change perfectly fine blower motor (for about 430$ + tax.

Thanks once more.
:-))

Zagi