Thermostat Problem or System Problem?
A house that never quite reaches the set temperature, a display that's blank or unresponsive, a system that short-cycles on and off, or rooms that feel warm even though the thermostat claims the target temperature was reached are all classic signs the thermostat itself is the problem rather than the compressor or coil. The tell is usually inconsistency: if a handheld thermometer near the thermostat reads several degrees off from what the display shows, the sensor inside the thermostat has likely drifted or failed.
That said, a bad thermostat can also mask a real system issue, since a miscalibrated unit will happily report a comfortable temperature while the house is actually still hot. That's why we check actual temperatures against the thermostat reading before recommending a replacement rather than assuming a thermostat is the culprit just because it's the easiest part to see.