Goodman furnace d: Dehumidification cooling with a single stage compressor
A lower case d means the system is cooling for humidity control rather than for temperature. The blower is deliberately running slower than normal.
Applies to: Goodman GMVM97, GCVM97 and Amana AMVM97 modulating gas furnaces with a two-character display, set up with a single stage compressor and a humidity-controlling thermostat.
What it means
Dehumidification mode is a real operating mode, not a fault, and it looks wrong to anyone who does not know it exists. When a humidity-controlling thermostat calls for moisture removal, the control slows the indoor blower. Slower air spends longer over the cold evaporator coil, gets colder, and condenses more water out of it — better moisture removal at the cost of less airflow. So the symptom is a system that seems to be running weakly on a humid day, which is exactly what it is meant to do. Lower case d is the single stage compressor version; d1 and d2 report low and high stage on a communicating two stage system.
Most common causes
- A humidity-controlling thermostat is calling for dehumidification.
- Humid weather, which is when this mode is designed to engage.
- The system configured for a single stage compressor rather than a two stage one.
How to diagnose it
- Note whether the weather is humid and whether the thermostat has a humidity setting. That usually explains it entirely.
- Reduced airflow during this mode is intended, not a fault.
- If the humidity setpoint has been set unrealistically low, the system will run in this mode far more than it should — that is a setting rather than a failure.
- If airflow is low in every mode rather than only this one, then look at filters and ductwork.
How to fix it
- Nothing, if the weather is humid and the thermostat is asking for dehumidification.
- If the system runs this way constantly, check the humidity setpoint on the thermostat before calling anyone.
- Reduced airflow in this mode is by design and should not be countered by raising blower speed.
Notes
This mode is a frequent source of complaints about weak airflow in summer. The furnace is not underperforming; it is trading airflow for moisture removal, deliberately.
Related
- d1 — Dehumidification, low stage cooling, communicating mode
- C — Compressor cooling with a single stage compressor
All codes for this manufacturer
Goodman and Amana furnace fault codes — every code, with what differs between models.
Models this code appears on
From the manufacturer's per-model database. If your model is not listed, this code may not exist on your board, or it may mean something different — check the model page.
What the fix costs
Run correctly, this mode costs nothing — the slow blower is the feature. Costs appear when it is misdiagnosed: a 'weak airflow' complaint that is really dehumidification working ends as a $75–150 diagnostic with nothing to fix (repair cost guide). The genuine repair scenario is weak airflow in every mode, not just this one; if that traces to the blower itself on these variable-speed furnaces, the blower motor cost guide puts variable-speed ECM work at $900–1,500+ installed. Establishing which of those two situations you have costs nothing: compare airflow in dehumidification against a plain fan-only call.
DIY or call a pro?
Check the thermostat's humidity setting and the weather before anything else — a lower-case d on a muggy day is the system obeying orders. The filter is yours as well. What is not DIY is countering the mode: raising blower speed to 'fix' the reduced airflow defeats the moisture removal and involves reconfiguring a communicating control inside a gas appliance. If airflow is poor in all modes with a clean filter, or the house stays damp despite long runs in this mode, book the visit and describe exactly which modes are weak — that sentence does half the diagnosis.
What this looks like
From the outside, this usually shows up as the blower runs when it should not — that walkthrough covers what to check in order, and when it stops being a homeowner job.