The answer to 'air duct sealing not working' is that there are several common causes, including improper installation, air leaks, and damaged or deteriorated seals. Symptoms may include drafts, uneven heating/cooling, and higher energy bills. The best solution is to have a professional HVAC technician inspect and diagnose the issue, then reseal the ducts properly.
DIY duct sealing can be effective for minor leaks, but larger issues or improper techniques can make the problem worse. It's generally best to call in a qualified HVAC specialist to ensure the job is done right and your system is functioning efficiently.