Thermostat display is completely blank and system does not run

Safety first: Turn off power to the furnace/air handler and outdoor unit at the breakers before opening access panels or touching wiring.

Steps to troubleshoot:

• 1. Check breakers: Verify that the furnace/air handler and outdoor unit breakers are not tripped. Reset if necessary.
• 2. Inspect thermostat wiring: Remove the Emerson thermostat from the wall plate and confirm that the R (or Rc/Rh) and C wires are firmly connected and not corroded or broken.
• 3. Check furnace control board fuse: Remove the furnace/air handler access panel and locate the low-voltage fuse on the control board. Replace with the same rating if blown.
• 4. Test for 24VAC (advanced): With a multimeter set to AC volts, measure between R and C at the furnace board. You should see approximately 24VAC. If not, the transformer or high-voltage supply may be faulty.
• 5. Verify power adapter (if used): If an Emerson power adapter kit is installed, confirm its connections to R and C at the control board and to the thermostat are secure and not damaged.
• 6. Replace thermostat if power is present: If 24VAC is confirmed at the thermostat sub-base but the display remains blank, the thermostat electronics have likely failed and should be replaced.

When to call a professional: If you cannot locate 24VAC at the control board or are uncomfortable using a multimeter, contact an HVAC technician.