Faulty exterior temperature sensor on Climatronic?

Hello everyone,
'Yesterday, my climate control system started heating instead of cooling, and the air conditioning isn't turning on, even though the outside temperature was around 22°C.'
When manually starting the air conditioning (using the button with the star symbol), the symbol briefly appears on the display and then disappears again. I'm familiar with this process; it happens in the winter when it's cold outside, and it's normal.
My current suspicion is that the external temperature sensor is either defective or providing inaccurate, low readings.
Can anyone tell me where the sensor is located (Audi 80, 1995, Avant model) and whether there's a way to access it through the climate control system? Perhaps someone has already encountered this problem and might even know of a cheap repair solution?
Thank you in advance, and greetings from Augsburg.
Stefan.

Hi,

Has the entire display ever flickered? Let's check the error memory; there might be something stored in it.
After 8 years, it's also quite possible that the refrigerant has simply leaked out. The normal emission rate is, on average, 8% per year.

Do you already have R134a in it? Then, at least, there won't be any problems with the supply.

Hello, yes, but if the refrigerant is missing, then the device won't HEAT up!!

I would also check for a faulty outdoor temperature sensor. Tap the sensor.

Hi,
Thank you for your contributions. So far, the display hasn't blinked. Sometimes, the air conditioning still turns on (probably when it's relatively warm outside, like it was this afternoon). B.) I don't know what type of refrigerant is in it.
@Kombiblue: The heating works even without the air conditioning, right?

Does anyone happen to know where the outdoor thermometer is? Are you paying attention?
Regards,
Stefan.

Hi,

The CT measures at multiple points, so that if a sensor fails or if the values are implausible, an error message is generated. The system is capable of checking the signals for plausibility.

For example, in the G IV, the outside temperature is measured both at the bumper AND in the intake manifold of the water separator. It's highly unlikely that both sensors are malfunctioning. At most, the one that measures the internal temperature might be providing incorrect values, as it's a simple sensor. Perhaps the fan in front of this sensor has failed, or the intake opening is completely clogged? It should be located in the dashboard, near the control panel. If BOTH external sensors or the internal sensor fail, the display on the G IV will blink for 15 seconds after startup.

To the best of my knowledge, older CT control units do not have their own diagnostic mode, unlike, for example, those in the Golf IV. So, you're only able to proceed by reading the error codes from the vehicle's computer.