HVAC Issue after messing about with lights

[Tavish_a3]

HI All. I'm new here. I am not a car pro but I am a motorcycle engineer so should be able to follow the techy bits.

I have had a quick search and cannot see a reliably identical issue being discussed so here goes

My 2006 Audi A3 2.0 FSI has no activity in the HVAC area. NO backlights, no fan, no defroster, no LCD, nothing.

It didn't randomly do it but after a service so I don’t believe that is a coincidence so let me give you a quick background. The number plate lights haven’t worked for a while. I had tried changing bulbs but didn’t work so I left it alone. Recently the tail lamp bulb went which was not ignorable so I replaced it and seen that also went kaput. I wanted to clean the connectors but a service was due so I asked the mechanic to have a look at that. He fixed the tail lamp (new bulb, connectors cleaned) and also determined that there was no power to Number plate lights and that this was turned off at the CAN bus level. He had checked the ground etc so declared this a separate job for another time. He did fix the tail lamp though so I wasn’t too fussed. Some other things were sorted with the suspension arm so the battery was disconnected and reconnected – maybe relevant.

I drove off on this chilly evening and realised the HVAC was off so I hit the ‘Auto’ button – aaaand nothing. So I drove back and the mech patiently checked everything on his Snap-On diags module, reset everything, recalibrated, took the stereo off and checked the HVAC connector etc etc. Disconnected, reconnected the battery. Checked all fuses in both boxes. He then declared the HVAC unit dead, and I find that a very improbable thing to happen randomly.

If you clear the codes, U0164 comes back immediately. The only other error is that the alarm horn is not working which is how its always been. If the alarm goes off you just see the indicators flashing. Again, never bothered me enough. The rear lights and rear wiper motor all work fine. The washer fluid to the rear wiper doesn’t make it all the way but drips down the rear wheel – I need to sort that but not sure if that is related in causing water damage to something? I cant think of any other issue with the car

My car was mostly fine before the service and now it's trying to cook me alive as even though the blowers etc font do anything once the engine warms up there is very warm air coming through the vents

This is the type of electronic gremlin that I think could benefit from the experience of someone who has been down this road. Thanks in advance!

[vag_tech]

What are the codes, with their descriptions?

[Tavish_a3]

What are the codes, with their descriptions?

Thanks for the response. I cant recall exactly but it was U0164 and something to do with the the fact that there is no comms with the HVACCM.

[vag_tech]

If you can get a full scan with VCDS and post here that would be tremendously helpful.

[Tavish_a3]

Update:

The mech had it back and fixed it.

He said there was a relay behind the fuses that had bad connectors, and this came up with systematic troubleshooting. Everything works now, thanks for your help!