Goodman
Loss of 24V Control Power
Thermostat is blank and furnace does not respond.
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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 low-voltage fuse on Goodman board, Shorted thermostat wire, Failed 24V transformer, Miswired outdoor unit contactor
How to Fix / Troubleshooting
Safety: Turn off power to furnace and outdoor unit before working on low-voltage wiring.
Steps:
- Check low-voltage fuse: Replace the 3–5A fuse on the control board if blown. If it blows again, there is a short.
- Inspect thermostat cable: Look for damaged insulation, especially where the cable passes through metal.
- Disconnect outdoor unit: Temporarily disconnect Y and C wires going to the outdoor AC at the furnace. Replace fuse and test. If fuse holds, the short is likely in the outdoor unit or its wiring.
- Test transformer: Verify 24 VAC output from the transformer. Replace if no output with proper primary voltage.
Once 24V is restored, the thermostat should power up. Persistent fuse blowing requires professional troubleshooting.
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Repair Difficulty
Medium
3/5
Required Part
24V Transformer
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