b9 Low indoor airflow

What the control is telling you

Airflow is lower than the control is asking for. The furnace may run with reduced performance or stay on low stage when high stage is called.

Applies to: GMVC95/AMVC95 upflow and *CVC9 counterflow two-stage furnaces

Likely causes

• Dirty filter
• Restricted ductwork
• Undersized ductwork

Test and repair steps

1. Check and clean or replace the filter.
2. Check ducts for blockage and open all registers.
3. If the ducts are undersized for the system, they need to be resized.

Settings for these units

• Normal status displays (7-segment) · Goodman/Amana GM9S96/AM9S96
• Normal status displays (7-segment) · Goodman/Amana GM9S80/AM9S80
• Normal status displays (7-segment) · Goodman/Amana GM9C96/AM9C96
• Minimum recommended filter size · Goodman/Amana GM9C96/AM9C96

Models that show this code

10 models in Goodman/Amana *MVC95/*CVC9 two-stage ComfortNet

Other codes on the same units

• b4 Blower motor trip (lost rotor control or high current)
• b5 Blower motor locked rotor
• b6 Blower motor over/under voltage or over temperature
• b7 Blower motor missing parameters
• C1 Low-stage cooling
• C2 High-stage cooling
• d0 No shared data on the control
• d4 Memory card data rejected