Goodman furnace d1: Dehumidification, low stage cooling, communicating mode

d1 means the system is removing humidity while cooling on the compressor's low stage, on a communicating system. It is a normal operating mode.

Applies to: Goodman GMVM97, GCVM97 and Amana AMVM97 modulating gas furnaces with a two-character display, on a communicating system with a two stage compressor.

What it means

On a communicating system the furnace, the outdoor unit and the thermostat exchange information rather than simply switching each other on, so the control knows which compressor stage is running and reports it. d1 is dehumidification with the compressor on low stage — the combination that removes the most moisture for the least cooling, because a low stage compressor and a slowed blower together produce a long, gentle, very effective dehumidifying cycle. This is the mode a well set up variable capacity system spends a lot of a humid summer in, and it is the one most likely to be mistaken for underperformance.

Most common causes

• A communicating thermostat calling for dehumidification with the compressor on low stage.
• Humid conditions with a modest cooling load, which is precisely what low stage dehumidification is for.
• A two stage or variable capacity outdoor unit on a communicating system.

How to diagnose it

1. Note the weather and the thermostat's humidity setting first.
2. Long, low-output cycles are the intended behaviour here rather than a symptom.
3. If the house feels cold and clammy rather than cool and dry, the humidity setpoint may be too aggressive.
4. Compare against d2, which is the same mode with the compressor on high stage.

How to fix it

1. Nothing. This is the system doing its most efficient dehumidification.
2. Adjust the humidity setpoint at the thermostat if the system stays in this mode more than wanted.
3. Do not interpret the long run times as short cycling or as a fault — they are the opposite.

Notes

Homeowners moving from a single stage system often report that a variable capacity one 'runs all the time'. In this mode that is correct and is why it removes humidity so much better.

Related

• d2 — Dehumidification, high stage cooling, communicating mode
• C1 — Low stage compressor, cooling mode

All codes for this manufacturer

Goodman and Amana furnace fault codes — every code, with what differs between models.

Sources

• Goodman Manufacturing — Diagnostic Code Identification System (model-specific fault code lookup)