Airflow is lower than demanded. The air conditioner or heat pump operates at reduced performance, or in low stage when high stage was expected. The display shows b9.
Homeowner part this code names: furnace air filter.
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Goodman b9 means airflow is lower than demanded. The system can keep running at reduced performance, or stay in low stage when high stage was expected. Causes are an indoor blower motor problem, blocked filters, restrictive or undersized ductwork, and an indoor and outdoor unit mismatch. The filter is the homeowner check. Motor, duct size, and the approved system match are technician checks. b0 is the blower that is not running at all.
Likely causes
- Indoor blower motor problem
- Blocked filters
- Restrictive or undersized ductwork
- Indoor and outdoor unit mismatch
Safe checks for b9
- With the blower off, check the filter and replace it if it is blocked. The chart says to clean or replace filters as needed
- Techniciancheck the indoor blower motor, resize restrictive ductwork, and verify the indoor and outdoor units are an approved match. The notes point at the specification sheet for airflow and maximum external static pressure
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if b9 remains after a clean filter. Low stage when you expected high stage can be a system match, which is not a thermostat setting.
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Parts & tools for this fix
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Furnace and AC air filter: guide
In this code: Blocked filters
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