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 commercial split systems, bring intermittent operation and controls into the scope discussion. Ask whether a partial replacement is approved and practical for the existing equipment. Compare it with a complete matched option using serviceability and total scope, not only the cost of the failed component.