Start with airflow
Blocked vents, closed dampers, dirty filters, and return-air limitations can contribute to uneven temperatures.
The house is part of the system
Sun exposure, insulation, windows, room layout, and duct design can all affect comfort. Not every hot or cold room means the HVAC unit itself is failing.
Diagnosis should look beyond equipment
Persistent room-to-room differences may require evaluation of airflow, ductwork, controls, and home conditions together.
Safety note: If you smell gas, see smoke or fire, suspect carbon monoxide, or believe there is an immediate safety danger, leave the area as appropriate and contact the relevant emergency or utility service. Do not treat an active safety emergency as a routine HVAC appointment.