Responded to a service call where the thermostat wasn’t responding—customer had no cooling. Found a blank display on a Honeywell digital thermostat due to a blown 3A fuse on the control board. Replaced the fuse, restored 24V power, and verified system communication. Performed full AC maintenance on a 3-ton York unit: cleaned condenser coil, flushed drain line, and confirmed 10°F subcool and 13°F superheat. System is cooling properly again. Thermostat and AC now working like new!