2004 Mercury Marquis Vacume Leak

If the blower slows then check battery for cleanliness and belt being tight as it may be a bad belt and tensioner. To check for a vacuum leak especially on heater listen for hissing around vacuum and use your hand to follow tubes. See if you get vacuum to one of the motors tha tare supposed to be working and pull line off and stick finger there, if vacuum then the motor is no good