What can cause weak airflow?
Weak airflow can come from more than one heating & air conditioning branch. Operating conditions, warning behavior, scan data, and physical tests are needed to separate the supported cause from look-alikes.
Plausible causes
- Cabin HVAC airflow, temperature-control, or refrigerant-system concern
- Airflow or distribution fault
- Heating/cooling production fault
Useful next checks
- Record ambient temperature, time to failure, strong-versus-weak airflow, idle-versus-road behavior, one-zone versus all-zone, odor, fogging, and water location. Do not open refrigerant or high-voltage HVAC components.
- HVAC/body/powertrain module scan and PID plausibility
- Blower command/current, filter, doors, evaporator temperature, and drain
Sources and method
This answer provides hypotheses and a verification plan, not a component verdict. Exact repair procedures require authoritative service information for the specific vehicle.
HVAC System Description and Diagnostics · NHTSA / General Motors