Goodman · Furnace

EEH Twinning error

Low severity Goodman/Amana GM9S96/AM9S96Goodman/Amana GM9S80/AM9S80Goodman/Amana GM9C96/AM9C96

What the control is telling you

The twinning feature (two furnaces linked through the TWIN terminal) is not working.

Applies to: Goodman/Amana/GMC gas furnaces, 9-speed ECM, 7-segment control. Two-stage 96%: AC9C96, AM9C96, GC9C96, GM9C96. Single stage 80%: VC9S80, VM9S80, AC9S80, AM9S80, GC9S80, GM9S80. Single stage 92/96%: VC9S96, VM9S96, AC9S96, AM9S96, AM9S92, GC9S96, GM9S96, GM9S92

Likely causes

Twin wiring loose or wrong
Furnaces not the same model or set differently
Furnaces powered from opposite panel legs
Control board fault

Test and repair steps

Check the TWIN terminal wiring between the two furnaces and the thermostat wiring per the twinning diagram.
Both furnaces must be the same model with the same staging and speed tap settings.
Each furnace needs its own 115 VAC supply, with L1 on the same panel leg: L1 to L1 between the furnaces must read 0 V.
If the wiring and settings are correct, replace the integrated control board.

Settings for these units

Normal status displays (7-segment) · Goodman/Amana GM9S96/AM9S96
Normal status displays (7-segment) · Goodman/Amana GM9S80/AM9S80
Normal status displays (7-segment) · Goodman/Amana GM9C96/AM9C96
Minimum recommended filter size · Goodman/Amana GM9C96/AM9C96

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Source: Goodman RS6612022r1 (GM9S92/GM9S96/GC9S96 service), 1 Stage Troubleshooting Codes, p.29-30; Goodman RS6621008r2 (GM9S80 service), p.32-33; Goodman RS6612020r1 (GM9C96 service), 2 Stage Troubleshooting Codes, p.35-36. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

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.