The answer to 'why is my HVAC system short cycling' is that your HVAC system is turning on and off too frequently, which can be caused by several common issues. Short cycling can be a sign of problems with the thermostat, the compressor, airflow restrictions, or other components in the system.
Some of the most common causes of short cycling include a faulty thermostat, a problem with the compressor, issues with the air filter or ductwork, and incorrect system sizing. If the thermostat is malfunctioning or not properly calibrated, it may be causing the system to turn on and off too often. A compressor issue, such as a refrigerant leak or electrical problem, can also lead to short cycling. Restricted airflow from a dirty air filter or blocked ductwork can also cause the system to short cycle as it struggles to maintain the desired temperature.