What to know
A blank screen is one clue. Warm air, ice, water, and unusual cycling point to very different parts of the system.
Thermostats get blamed because they are the part of the system you can see. But a cooling problem can start at the drain line, the outdoor equipment, an electrical connection, the filter, or the ductwork.
Pay attention to the symptom. Warm air from every vent is different from normal cooling with one hot room. A unit that clicks and stops is different from one that runs for hours. Water near the air handler is different from condensation on a supply grille.
Those details help a technician narrow the search faster. When you call, describe what changed, when it started, and whether both the indoor and outdoor equipment are running.
