grand marquis ac control issues

Usually air flow issues on these cars is the blend door actuator. The blend door actuator moves the blend door to direct heat and a/c. The entire dash needs to be removed to replace the blend door correctly, but there are some short cuts posted on the web. Do a "google" search for mercury blend door actuator replacement and make sure your symptoms are caused by the blend door actuator. If you do replace the actuator make sure you only use a genuine Ford / Mercury part as some of the aftermarket actuators are inferior quality.