HVACopediaCarrier · Furnace
10.1 L1 polarity fault
What the control is telling you
The control sees reversed 115-V line/neutral polarity. The status LED flashes rapidly and the furnace will not operate.
Applies to: Carrier 59SC6A
Likely causes
- Hot and neutral reversed at the furnace junction box
- Reversed polarity in building wiring or power cord
- Poor or missing ground
Test and repair steps
- Warning: Turn off power at the disconnect before working in the junction box; verify with a meter.
- Confirm the LED is flashing rapidly and display shows 10.1.
- Measure voltage L1 (black) to ground should read about 115 V; neutral (white) to ground should read near 0 V.
- Correct reversed hot/neutral at the J-box or upstream source.
- Verify the furnace ground is continuous and the green/yellow ground to the gas valve and manifold bracket is intact; the control locks out if not grounded.
- Restore power and confirm the code clears and the furnace operates.
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Source: Carrier 59SC6A Installation, Start-up, Operating and Service Instructions, Fig. 60 Service Label p.54; 115-V Wiring and Start-up General p.55. Summarized in our own words; check the original manual for your model.
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For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.