9 blinks
Moderate
York · HVAC Systems (AC, Furnaces, Heat Pumps & Thermostats)
Grounding / Polarity Issue
Quick Answer
Error code 9 blinks on your York HVAC Systems (AC, Furnaces, Heat Pumps & Thermostats) means: Grounding / Polarity Issue. This is usually fixable — see the step-by-step guide below.
Likely Causes
How to Fix It
1
Use a multimeter to verify 120VAC between hot and neutral at the furnace disconnect
2
Confirm 120VAC between hot and ground (should match hot to neutral reading)
3
Check for less than 2VAC between neutral and ground at the furnace connection
4
Inspect the furnace junction box wiring for reversed hot and neutral connections
5
If the wiring at the furnace is correct, a licensed electrician should check the upstream circuit
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Wire connectors
Ground wire
Disconnect switch (if faulty)
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