American Standard Low Voltage Drop / Transformer Overload

Thermostat goes blank when furnace starts, then comes back on after a while

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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

Shorted low-voltage accessory (humidifier, UV light), Undersized 24V transformer, Short in thermostat cable, Faulty American Standard control board drawing excess current

How to Fix / Troubleshooting

Safety: Turn off power before disconnecting low-voltage devices.

  • Isolate accessories:
    • Disconnect humidifier, air cleaner, and other add-ons from R and C.
    • Test furnace operation with only thermostat connected.
  • Inspect thermostat cable:
    • Look for damage or shorts to metal surfaces.
  • If issue persists, have a technician test transformer load and replace transformer or board as needed.
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Repair Difficulty

Hard 4/5

Required Part

24V Control Transformer
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