I just came across this interesting little trick for diagnosing blocked CCV in the Volvo forum:
With the oil cap sealed, engine on, stick a balloon over the dipstick tube and see if it inflates. If it inflates you need to service the PCV system.
I think he meant with the dipstick removed, so the balloon goes over the dipstick housing.
No balloon, no problem, get an old dish washing glove, cut a "finger" off and tie it with rubber band.