Carrier
No Power to Thermostat
Thermostat screen is completely blank and system does not respond to any inputs.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blown 3–5A low-voltage fuse on Carrier control board, Failed 24 VAC transformer in furnace/air handler, Disconnected R or C wire at thermostat, Shorted thermostat cable causing fuse to blow
How to Fix / Troubleshooting
Safety first: Turn off power to the furnace/air handler at the breaker before opening panels.
- Step 1 – Check breakers: Verify that the furnace/air handler and outdoor unit breakers are not tripped. Reset if necessary.
- Step 2 – Inspect control board fuse: Open the blower compartment and locate the automotive-style fuse on the Carrier control board. Replace if blown with the same amperage. If it blows again, there is a short that must be found.
- Step 3 – Verify thermostat wiring: At the thermostat, ensure R and C wires are firmly connected. At the control board, verify the same.
- Step 4 – Test transformer (advanced): With power on and caution, measure voltage between R and C at the control board. If no 24 VAC is present, the transformer or board is likely failed.
- When to call a pro: If the fuse repeatedly blows or the transformer is failed, contact a Carrier technician for further diagnosis and replacement.
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Repair Difficulty
Medium
3/5
Required Part
Carrier Furnace/Air Handler Control Board
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