FieldBench
Goodman codes

Goodman

b3

Protect

Motor limiting (power / speed / temp)

ECM is folding back on power, speed, or temperature. Furnace keeps running at reduced CFM.

Walk b3 in Diagnose

3 plates — walk the one on the cabinet

First check

1 Airflow before you touch the limit

On Goodman GMVC80 a limit is airflow or overfire until proven otherwise. Do not replace the limit first. Filter, blower wheel, A-coil, and the heat-speed setting for THIS motor (tap, model plug, or communicating CFM — not a sister SKU chart). This is Category I metal vent. There is no 96% collector or PVC trap to prime.

Expect: Rise in the rating-plate window. Static vs this cabinet’s blower chart.

The rest of the walkthrough is Diagnose.

On the plates

  • Total external static vs the GMVC96 blower chart. Media cabinet + dirty coil is the usual.
  • IFC cool/heat CFM set higher than the duct can take.
  • Wheel rub or restriction that is not quite a lock.
  • This is Category I metal vent. There is no 96% collector or PVC trap to prime.
  • Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.
  • Filter, coil, and total external static vs the AMVC96 blower chart.
  • Return undersized or a 5" media cabinet the installer added.
  • High ambient around the motor (closet, no ventilation).

Plates that use b3

Same number, other makers

b3 on Goodman is not the same code on these plates.