Thermostat display completely blank, system not responding

Safety first: You will be working near line voltage inside the furnace/air handler. Turn off power at the breaker before removing any panels.

Steps to restore power to a dead thermostat:

• 1. Check breakers and switches: Verify the furnace/air handler breaker is ON and any service switch near the unit is also ON.
• 2. Inspect furnace control board fuse: Remove the blower door, locate the Goodman control board, and check the low-voltage fuse. Replace with the same amperage if blown, but investigate for shorts if it blows again.
• 3. Measure 24VAC at furnace: With power on, measure between R and C on the control board. If no voltage is present, the transformer or board may be defective and should be serviced by a professional.
• 4. Check thermostat wiring continuity: With power off, verify continuity of the R and C conductors from the furnace to the thermostat. Repair or replace damaged cable.
• 5. Test thermostat on known-good circuit: If 24VAC is present at the thermostat wires but the display remains blank, try a known-good thermostat. If it powers up, the original thermostat has failed and should be replaced.