Goodman furnace P1: Low stage compressor, heating mode
P1 means the heat pump is heating the house on its low stage, and the furnace is idle. On a dual fuel system this is the cheaper heat source doing the work.
Applies to: Goodman GMVC96, GMVM97, GCVC96, GCVM97 and Amana AMVC96, AMVM97 series gas furnaces with a two-character alphanumeric display, installed as part of a dual fuel system with a heat pump.
What it means
In a dual fuel system the heat pump handles heating in milder conditions because it is cheaper to run, and the gas furnace takes over when it gets cold enough that the heat pump becomes inefficient. P1 means the heat pump is running on low stage and the furnace is standing by. Seeing this while the house is warm is confirmation the system is doing what it was designed to do — using the less expensive heat source. It is worth documenting because a homeowner checking the furnace display during heating and seeing a compressor code can reasonably wonder whether something is wired wrongly.
Most common causes
- The heat pump is providing heat on low stage. This is normal dual fuel operation in mild conditions.
- Outdoor conditions above the switchover point where the heat pump is more economical.
- The system correctly selecting the cheaper heat source.
How to diagnose it
- Confirm the system is dual fuel. If there is no heat pump, this code should not appear.
- Note the outdoor temperature. Heat pump operation in mild conditions is correct.
- Note whether the system switches to the furnace when it gets colder, which confirms switchover is working.
- If the heat pump runs in very cold weather while the house does not keep up, the switchover point may be set wrong.
How to fix it
- Nothing to fix. This is normal dual fuel operation.
- If the system never switches to the furnace in cold weather, have the switchover configuration checked.
- If the furnace runs when the heat pump should be handling mild conditions, that is also worth checking — it costs more to run.
- Do not use emergency heat as a default setting. It bypasses the heat pump entirely and runs the expensive source.
Notes
The switchover point on a dual fuel system is a real setting with real cost consequences. Set too high, the furnace runs when the heat pump could have; set too low, the heat pump struggles in conditions where it is inefficient.