I don't know for sure, but Volvo cruise control actuators are normally
under the dash now, attached to the gas pedal.  There is a vacuum pump
under the hood somewhere with a hose that goes to that acuator, chances
are there's some water in that hose freezing.

Or if you have electronic throttle (no throttle cable), then there is no
cruise control hardware, the fuel computer just controls the throttle
actuator.  If there's a problem with this system, then you should have
some kind of warning light on your dash.

I would guess that this alsoaccounts for the s40 as weel for my 850,
Acording
to the manual the crouse conrol switches off if it detects that the driven
wheels are slipping.
it has not been cold enought to try this to se if this is happens