Mercury Grand Marquis A/C air distribution issue with intermittent airflow to defrost and heater vents on Mercury Grand Marquis

Some Mercury Grand Marquis owners report experiencing intermittent airflow issues, where airflow unexpectedly shifts to the defrost and heater vents. This problem may stem from the default position of the system, which directs airflow to the defrost vents when there is low or no vacuum. Additionally, insufficient refrigerant in the AC system can lead to a frozen evaporator coil, resulting in weak airflow from the AC vents. Owners may also encounter problems with the blend door or digital control system, which can disrupt proper air distribution. A faulty blend door actuator or a clogged evaporator could further contribute to these issues. In some instances, the AC may default to the defrost and floor vents, necessitating troubleshooting to redirect airflow. To resolve these concerns, it is advisable for owners to check for vacuum leaks, ensure the AC system has adequate refrigerant, inspect the blend door and actuator for malfunctions, and consider cleaning or replacing a clogged evaporator.