VW Bora AC Failure Linked to Heat Exchanger Sensor

Had a similar issue with my 2003 VW Golf 1.6 petrol last summer. Have some experience working on VAG cars and their HVAC systems. The symptoms were identical, AC not engaging and error codes related to the temperature sensor system. Initially thought it was just the heat exchanger sensor needing calibration, but after having it properly diagnosed, the control unit itself was faulty. Took it to a specialist workshop that confirmed the temperature gauge and sensor readings were inconsistent. They tested the engine cooling system thoroughly before replacing the AC control unit. Total repair cost was 980€ including parts and labor. The repair solved all issues, AC works perfectly now and no more error codes. Would recommend getting a proper diagnosis before replacing parts, as these symptoms can point to multiple components in the HVAC system. What error code are you getting specifically? Also, does your temperature gauge show normal readings while driving? This information would help determine if you are dealing with the same issue.

Thanks for sharing your experience. My Bora had its last service at 116400km, about 2 months ago. The error code showing is P0117. The temperature gauge fluctuates while driving, sometimes showing normal readings but occasionally jumping higher for short periods. The coolant leak check came back negative, but the cooling system definitely seems unstable. The AC issue started right after a particularly hot day when the temperature warning light briefly came on. Based on your feedback, I should probably get the control unit checked along with the sensor. Getting nervous about potential damage if I keep driving it like this. Would the control unit replacement also require recalibrating the temperature sensor, or is that a separate procedure?

Thanks for those extra details about your Bora. With my Golf having shown similar symptoms, I can better understand your concern about the fluctuating temperature readings. The P0117 code typically indicates a sensor malfunction in the cooling system circuit, but my experience proved that the control unit can cause false sensor readings. In my case, the temperature sensor was actually fine, the control unit was misinterpreting the signals. When the workshop replaced my control unit, they did perform a complete system calibration as part of the repair process. The procedure involves calibrating all sensors connected to the heat exchanger and cooling system to ensure proper communication with the new unit. The temperature fluctuations you describe sound very similar to what I experienced. These unstable readings often indicate a failing control unit rather than just a temperature sensor issue. Given that your problems started after a heat-related warning, having the full system diagnosed is definitely the safer approach. For reference, after my repair the temperature readings stabilized completely and the AC has worked flawlessly. Total vehicle maintenance time was about 4 hours including all testing and calibration procedures. Would recommend getting this checked soon, as continuing to drive with potentially inaccurate temperature readings could lead to more serious issues with your cooling system.

Really appreciate the detailed information about your Golf repair experience. I just checked my odometer, now at 117200km, so about 800km since that last service. After hearing about your repair outcome, I will definitely get both the control unit and sensor checked. The temperature fluctuations are getting more frequent, especially during longer drives. Yesterday it jumped three times during a 30-minute trip. The vehicle maintenance costs you mentioned are higher than I hoped, but makes sense given the complexity of the heat exchanger system and needed calibration work. Better to fix it properly than risk engine cooling problems. Made an appointment at a workshop for next week. Will make sure they know about the P0117 code and check the entire cooling system, not just the temperature sensor. Getting this sorted before summer really hits seems like the smart move. Does it matter if I keep using the car until the appointment? Planning to avoid any long trips, but still need it for short commutes.