Heil Loss of 24V Control Power

Heil air conditioner thermostat display is blank and system does not run

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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 3–5A fuse on indoor control board, Open transformer, Shorted thermostat cable, Tripped float switch cutting R circuit

How to Fix / Troubleshooting

Safety first: Turn off power to the furnace/air handler before accessing the control board.

  • Step 1 – Check indoor fuse: Locate and inspect the low-voltage fuse on the control board. Replace with same rating if blown.
  • Step 2 – Inspect thermostat wiring: Look for shorts where the cable passes through metal or is stapled.
  • Step 3 – Check float switch: If equipped, see if the condensate float switch has tripped due to a clogged drain. Clear the drain and reset.
  • Step 4 – Transformer test: A technician should measure 24V output from the transformer and replace if open.
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Repair Difficulty

Medium 3/5

Required Part

24V Transformer
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