Thermostat display is completely blank and system does not respond

Safety first: Turn off power to the furnace/air handler at the breaker before removing access panels or touching wiring.

• Step 1 – Check other equipment: See if the furnace/air handler has power (look for status LEDs or blower operation). If it is dead, check the breaker and service switch.
• Step 2 – Inspect thermostat wiring: Remove the thermostat from the wall and verify that the R and C wires are firmly connected and not corroded or broken.
• Step 3 – Test voltage at thermostat: With power on and using caution, measure between R and C at the wall plate. You should see about 24 VAC. If not, proceed to the indoor unit.
• Step 4 – Check furnace board fuse: At the indoor unit, locate the control board and inspect the low‑voltage fuse. Replace if blown, but also inspect the thermostat cable for shorts that may have caused the fuse to blow.
• Step 5 – Test transformer: Measure voltage at the transformer secondary. If there is no 24 VAC output, replace the transformer.
• Step 6 – Replace thermostat: If proper voltage is present at the thermostat but the display remains blank, the thermostat electronics have likely failed and the thermostat should be replaced.