Goodman Furnace: Check transformer phasing on unmarked transformers
Check transformer phasing on unmarked transformers on a Goodman furnace: Some electronic boards that use flame rectification need the low voltage side to be in phase with the line side. If a transformer has no phasing marks, you have to find out yourself. Wrong phasing can stop the board working at all.
Applies to: Gas furnaces ACVC96/AMVC96/GCVC96/GMVC96
Common causes of check transformer phasing on unmarked transformers
- Unmarked transformer wired with the secondary reversed
- Transformer replaced without checking phasing
- Board with flame rectification that will not accept out-of-phase power
- Flame sense faults appearing right after a transformer swap
How to fix check transformer phasing on unmarked transformers: step by step
- With power on, measure from the low voltage common/ground to the hot line leg
- About 96 V means primary and secondary are in phase
- About 144 V means they are out of phase, so reverse the low voltage wires
- The readings are approximate, so a clear gap between the two numbers is what matters
- Wire the furnace to match the phasing. Some transformers have phasing symbols to help identify the correct orientation
- Power off before changing wires, then retest and confirm the board starts normally
If the unit shows an error code, look it up: Goodman Furnace codes
Source: Goodman GMVC96 service and troubleshooting manual, p. 42. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.