If your car's air conditioner is only cooling in one vent out of four, there could be a few possible reasons for this issue:
Damaged or disconnected air duct: The air ducts in your car's ventilation system are responsible for directing the cooled air to different vents. If one of the ducts is damaged, disconnected, or blocked, it can restrict the airflow to the affected vent. This could be due to a loose connection, a damaged duct, or debris blocking the airflow.
Malfunctioning blend door: The blend door is responsible for directing the airflow to different vents. If the blend door is stuck or malfunctioning, it may not be opening or closing properly, leading to restricted airflow to certain vents.
Clogged or faulty blower motor: The blower motor is responsible for pushing the air through the vents. If the blower motor is clogged with dirt or debris or if it is malfunctioning, it may not be able to supply enough air to all the vents, resulting in poor airflow to some of them.
Control panel or actuator issues: The control panel in your car allows you to adjust the temperature and airflow settings. If there is a problem with the control panel or the actuator that controls the vent selection, it may not be functioning correctly, leading to improper distribution of the cooled air.
To diagnose and fix the issue, it is recommended to take your car to a qualified mechanic or an automotive air conditioning specialist. They will be able to inspect the system, identify the underlying cause, and perform the necessary repairs or replacements to restore proper airflow to all the vents.