[A4] Heater Issues

[Brizax at aol.com]

make sure the AC compressor is in fact running when you turn the heat on,  
you will hear what it sounds like if you have the car running and switch it off  
and on with the hood up, then try heat, listen to see if the compressor is  
running, otherwise make sure your thermostat is good and not gone or  jammed

Just had  the timing belt job done on my 01' 1.8T, at a supposedly  reptuable
independent shop.  Immediately after, the cabin heater  doesn't heat up.
Also for about a week, the water temp gage looks like it  has a bad sensor or
maybe an air bubble: needle jumps between cold and  midway even after warm,
but this eventually goes away and works fine after  I bleed the air a few
times.  After bringing it back for the heater  issue, they tell me that hot
water is circulating just fine, temp sensors  are fine, the heater flap motor
is responding to their VAG-com fine, but  they suspect that the AC head unit
is bad.  During use, the AC head  unit seems to work fine, except for the
lack of hot air coming out of the  vents.  This sounds reasonable enough to
me, but the timing with the  TB/T-Stat/H2O Pump job and the temp gage seems
wrong to me.  Has this  happened to anyone?  Any ideas?  Any things to check
before I  order (and change myself) the big $$$ AC head unit?