Not getting hot air from HVAC/climate heater.
Also sometimes coolant temp gauge goes to 'cold' from middle.

Found:
01039 - Coolant Temperature Sensor (G2)
30-00 - Open or Short to Plus

Replaced G2 sensor (G62 also in there IIRC).

Gauge showing properly.

Heater still blowing cold.

Heater core was flushed not too long ago.
Timing belt with water pump done not too long ago.
'burbed' the heater hose with the white dot at firewall (did not seem air coming out).

Any suggestions for further troubleshooting?

 

Didn't I just read that you froze up your block?

Heater core will take a while to thaw out if there is no flow of hot coolant to help it heat up. I had mine freeze up on me last year with a surprise snap cold spell. ended up making a heated fan in the garage and stuck a dryer vent into the cabin intake to pull in forced hot air from my garage heater. That helped thaw it out quicker than just the car running on its own.

Good luck.

 

I just experienced 03 A4 not blowing heat. I got a chemical flush of my heater core paid $400 the place i went to says the local audi dealership sends the cars to him and they charge an enourmous amount for a heater core. Cancelling my appointment at the dealer, heat is very hot now