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.