Seat Tarraco Air Conditioning Problems

That sounds familiar. I have a Seat Tarraco as well, although I'm not sure about the year, and I had a similar thing happen last summer. The temperature gauge was all over the place, and the HVAC system just wouldn't kick in. First, have you checked for any coolant leaks? A low coolant level can cause all sorts of temperature-related issues. Also, have you had the error codes read? That can point you in the right direction.

I did check the coolant level, it seems fine. The error memory has a fault stored related to the 'Temperature sensor heat exchanger'. Does this sound like the same issue you had? Did you also have this error?

A specific error code for the temperature sensor on the heat exchanger makes things clearer. Yes, that's pretty much exactly what I experienced. Replacing the sensor might solve the problem, but in my case, it turned out to be a faulty air conditioning control unit as well, which was causing the sensor to throw errors. I'd recommend getting it checked out by a workshop with the appropriate diagnostic equipment. They can pinpoint the exact cause.

Took it to the workshop as you suggested. The temperature sensor on the heat exchanger was defective. The air conditioning control unit also needed replacing. Cost me 980€. Thanks for your help, much appreciated!