A/C not turning on after water pump repair

[erobinson]

I have a 2010 S4. Car overheated last week, figured it was the water pump or thermostat so had a local shop replace them. The mechanic only replaced the pump (said it was easier) and it was still overheating, but he thought the t-stat was fine because water was flowing, then he tells me he thinks my head gasket is bad. Long story short, took it to the dealer, thermostat WAS bad, and the secondary expansion tank had a hose loose causing coolant to spill (probably the first mechanic didn't tighten it). They also tell me my A/C pressure/temp switch is bad and my AC doesn't work.

I think that the first shop must have disconnected something, because my A/C worked great up until the moment the car overheated (AC started blowing less cold, and 30 seconds later the car is beginning to overheat). They wanted $550 to fix it.

Picked up the car today, runs great, no overheating, but when I press the A/C button it just lights up for a moment and then immediately the light turns off. It blows air just fine, all the controls work, but no cold air and the button won't stay lit.

TLDR: Does anyone know where the connection is to this sensor so I can check it for myself?

This is the trouble code:
Part #: 8T1820043AQ
Coding: 66102000 (hex)
Component: KLIMA 3 ZONEN
Fault codes:
00256 Givers for refrigerant pressure / temperature (G395)

[Sudz]

Does it blow cold in park or neutral?

Mine would blow cold in park or neutral, but didn't in drive or reverse.
I had to clear a code with a Vagcom, thanks to another forum members suggestion.

[erobinson]

A/C doesn't even switch on at all. Park/driving doesn't affect it. The AC unit in the dash turns on, displays everything correctly, fans blow, heat works. But, when you press the "A/C" button, it doesn't turn on. The light doesn't even stay lit after you let go.

[14S4GWM]

I remember just recently someone posted the same thing, I can't find the thread though.

[LYKUNO]

I remember just recently someone posted the same thing, I can't find the thread though.

Here's that post (00256).

[14S4GWM]

Link not working

[erobinson]

If someone can find the post I'd appreciate it. I think I've located the sensor, will try to access it tomorrow and see if it's simply a connection issue. Definitely don't understand how this could be connected otherwise to my overheating problem. The car has been running great otherwise since replacing the thermostat. Need to fix this with how hot it has been here lately.

[erobinson]

Replaced the sensor, still having the same problem. Any ideas?