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 preventive maintenance, bring intermittent operation and controls into the scope discussion. For an office or multi-unit facility, compare proposals by included tasks and documented reporting, not only annual price per unit. Discuss response arrangements and replacement planning explicitly.