York No Power to Control Circuit

York AC will not start at all; thermostat display is blank or unresponsive

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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

Tripped breaker, Blown low‑voltage fuse, No 24V transformer output, Loose thermostat wiring

How to Fix / Troubleshooting

Safety: Use caution when working around live circuits. Turn off breakers before removing covers.

  • Check breakers and disconnects: Reset any tripped breakers for the air handler/furnace and outdoor unit.
  • Verify thermostat power: If battery‑powered, replace batteries. If hard‑wired, check for 24V between R and C at the thermostat.
  • Inspect low‑voltage fuse: Replace the fuse on the York control board if blown, after finding and correcting any shorts.
  • Test transformer: Measure primary and secondary voltages. Replace the 24V transformer if there is no secondary output.
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Repair Difficulty

Medium 3/5

Required Part

24V Transformer
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