Follow the symptom from thermostat to equipment
For Rosemont service, note whether the thermostat display is active, whether the fan runs and whether heating and cooling behave differently. This gives a clear starting point without requiring a homeowner to test live electrical components.
If the system works intermittently, record when it stops and whether the thermostat still calls. A repeatable description is more useful than replacing a thermostat solely because the room feels uncomfortable.
For ductless mini-splits, bring intermittent operation and controls into the scope discussion. Compare a dedicated system for the problem room with modifications to existing central ducts. For multi-zone proposals, ask what happens when only one small room needs conditioning and how the controls coordinate operation.
