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 hvac repair, bring intermittent operation and controls into the scope discussion. Compare repair cost, equipment condition, parts availability and operational impact with planned replacement. A commercial proposal should state downtime assumptions and exclusions instead of promising uninterrupted operation.