vtraudt

Not getting hot air from HVAC/climate heater.
Also sometime 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?

lyleswk

My 2 cents: replace the heater core. You didn't put the mileage, but I also flushed a heater core with no results on a car with over 200K miles. Ended up replacing the heater core and immediately fixed the problem. The issue is unless you are meticulous and change your coolant every 2 years or so or do not know the history, the particles in the coolant will clog the heater core and flushing won't help. When I pulled my core, it is obvious Audi minimized the size by creating a core with very small passages.

vtraudt

How about running vinegar or CLR through the core?

lyleswk

I have heard that can work, but never tried. I am always nervous adding fluids / chemicals in a system that I can't completely flush out and what the impact of those chemicals have on other components, like the water pump in this case. If the core was easy to remove and you could soak it for a while and then flush well before reinstalling, then okay. But if you go that far, might as well replace as I think they are fairly inexpensive and time is money...

edit: that is a horrible run-on sentence...

vtraudt

My sentiments exactly. I have used vinegar for example to treat motorcycle tanks. But easy to flush out COMPLETELY (and not much 'parts' effected).
Would need plenty of confirmed first hand experience before trying it.

Prospeeder

Core is bad. Flushing will not cure it in most cases.And mileage isnt always a factor. I just did a core awhile ago with only 90k miles and well maintained. Its just a rather poor core design that packs full of debris and isnt possible to fully flush.