The answer to 'why is my installation' is that there could be several common causes, such as improper sizing, incorrect installation, or issues with the ductwork. Symptoms may include uneven heating/cooling, high energy bills, or the system not turning on at all. Solutions can range from adjusting the thermostat to replacing parts or even the entire system, depending on the root cause.
In many cases, it's best to call a professional HVAC technician to diagnose and fix the issue, as they have the expertise and tools to properly assess and repair the system. Attempting DIY repairs without the right knowledge and experience can lead to further damage or even safety hazards.