I have found many topics about this problem on various IV models around the web, but are still stuck. So hope someone can shed some light on this. Golf IV 1,9 TDI 4motion 131hp ASZ engine.
Suddenly there is very little warm air from the climatronic system. It doesn't blow completely cold, but when it is cold outside it is chilli inside the car even if I turn climatronic to maximum (HI). The blowing motor work.
What I have checked so far= There is enough coolant. The engine temperature sensor show 80°C on warm engine through VCDS. Temperature gauge steady at 90°C. Both coolant pipes that goes in through the firewall to the heating system are warm, which should mean there is coolant circulation through the heater core.
No fault codes on the climatronic system. Outside air sensor in front bumper (G17), fresh air duct temperature sensor (G89), footwell temperature sensor (G192), dash panel (G56) & evaporator temperature sensor (G263) all show realistic values in VCDS.
A few strange things I have noticed. Before this thing happened= when I was driving along and the outside air temperature were 0°C for example, and I came into a long tunnel (where it is warmer air) the red numbered temperature in the instrument window on the car would flash a few times when outside air temp got up to +4°C (as a warning, and the snowflake symbol would go away at +5°C). And the same driving out of the tunnel back into cold air the temperature would flash a few times when coming down to +4°C (as a warning about possibly icy roads, and the snowflake symbol would come on). Now it doesn't flash at all. And the snowflake symbol still stay on at +5°C, which it didn't earlier. Apart from that the temperature in the instruments show realistic figures.
Another thing is if I stay in ECON on the climatronic and turn the heat up from 20°C, 21, 22, 23, all they way up to 29°C or next step which is HI...somewhere along the way there at maybe 25 or 26°C it will stop blowing air out through the senter vents (the ones above the cup holder). I have no idea if this is normal or just happened now, because before this problem I usually only kept temperature around 22°C and it would be more than warm enough inside. But at lower temperature setting - let's say 22°C on the climatronic it blow air through the center vents...
By the way, the AC works as it should.