Buick GL8 Heat Failure Points to Ventilation Issue

Had a similar issue with a 2009 Buick LaCrosse last winter. The symptoms matched exactly, poor heating and check engine light, particularly noticeable when using the defrost settings. The problem turned out to be a failed HVAC control module connection. The air distribution was completely disrupted because the system couldn't properly regulate air flow between different ventilation zones. The windshield fogging was especially bad because the climate control system wasn't directing air properly. The repair involved replacing the wiring harness connector to the HVAC module and recalibrating the whole climate control system. It was a serious issue that required specialized diagnostic equipment to properly identify the fault codes. Without proper air circulation, the entire heating system was operating at reduced capacity. Would strongly recommend having a professional diagnose this, as these symptoms often indicate electrical issues rather than mechanical problems with the heater core itself. The connector failure can also affect other systems beyond just heating and air circulation if left unaddressed. This is a known weak point in this generation of Buicks, the connections can corrode over time and cause these exact climate control issues.

Thanks for sharing your experience with the LaCrosse HVAC unit issue. I recently got my GL8 fixed for similar symptoms, poor temperature regulation and dashboard panel errors. The repair took about 4 days total since they needed to order parts. Just wondering, do you remember roughly what the total repair cost was for your car? Also, has the climate control system worked properly since the fix, or have you noticed any other issues?

Glad I could help with your GL8 issue. For my LaCrosse, the total repair bill came to around 95 Euro for fixing the faulty defrost air distribution flap. The problem was traced to a bad cable connection that was disrupting the air distribution system. The climate control system has worked flawlessly since the repair. The temperature regulation is back to normal, and the ventilation system distributes air properly to all zones. Most importantly, the defrost mode now works exactly as it should, with strong airflow to the windshield. It sounds like we had very similar issues. These connection problems are usually straightforward fixes once properly diagnosed, and the repair costs tend to be reasonable compared to more complex HVAC repairs. The key is catching it early before it can affect other components of the air circulation system.

Thanks everyone for the input. After getting my GL8 checked, the mechanic found a faulty blower motor connection and damaged wiring in the HVAC unit. The total repair came to 325 Euro including parts and labor. The temperature regulation is working great now, heat comes through strong and steady. No more issues with windshield fogging or weak airflow. The check engine light is off and the ventilation system is back to normal. The shop had to order a specific wiring harness which took a few days, but the actual repair only needed about 4 hours of work. Much better than having to replace the entire heater core, which is what I initially feared. Definitely worth getting it fixed properly rather than trying temporary fixes. The heating performance is even better than before the problems started.