Volvo Repair: a/c blowing hot air 1998 volvo v70 200000km, 1998 volvo v70, volvo v70

Question
First warm day of the year and all there is coming out of the vents is hot air. Tried several times and no change.
Non-turbo 2.4l.
I read an earlier post about trying to tap the clutch, could this be it? If I tap it will I see the clutch move?
Second question, mechanic took off snows and said that a rear caliper had seized and wore down the pads. Apparently freed up caliper and changed pads, but now when braking aggressively it there is a loud groaning/shuddering sound from the rear. Seized again?
Thanks for your time.

Answer
Kevin, mechanic should have replaced the rotors as well.  As far as A/C, how is the freon level?  That is the first thing to check.  These cars are known for Evaporators leaking.  Its an expensive job to fix.  check freon levels first then try the tapping.  I would bet that its the EVAp that is leaking.  Roger