1999 Mercury Marquis • 124,000 miles

My 1999 mercury grand marquis LS blows hot air. After turning the ac / heat on and off it will eventually switch back over to cold a/c. A/C will run as long as you don't change the tempature. I did check the vacuum lines and they all look like they are in good condition.

I have removed the entire dash to check vacuum lines. I also removed the ac/heater temp control unit. You know where you turn on and off the ac defroster heat ECT ECT. Any help would be greatly helpful.

Nice site : -)
Stephen Tatro
December 17, 2011.

Check to see if you have a vacuum leak first, then check to see if your actuators are working. They are under dash on heat unit. Generic pic enclosed.

Dec 17, 2011.