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ICP · Furnace

10 Line voltage polarity

Medium severity ICP (F/G)9MAE Modulating Furnace

What the control is telling you

Line voltage polarity is wrong (or furnace not grounded); furnace will not heat. On twinned units also check 24 V transformer phasing.

Applies to: ICP F9MAE / G9MAE modulating variable-speed condensing gas furnaces (060, 080, 100, 120 kBtu/h)

Likely causes

  • 115 V hot and neutral reversed
  • Missing earth ground
  • Twinned units with transformers out of phase

Test and repair steps

  1. Warning: Turn off power before rewiring.
  2. Check polarity at the furnace junction box: hot (BLK) and neutral (WHT) correct.
  3. Confirm a proper earth ground to the furnace and control.
  4. If twinned, check low-voltage (24 V) transformer phasing.

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Source: ICP (F/G)9MAE Service and Technical Support Manual 440 04 4700 00, Figure 16 Troubleshooting Chart, p.35. 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.