My heat only works on the circulate air setting and on low only, HELP !!

[yokcarrie]

I have a 1997 Jeep Grand Cherokee, I am having heat issues. The heat will only work on the circulate setting on low. The blowers all work, the thermostat was changed, the heater core was flushed. And as of this morning, my windows are frosting from the inside !! Please, any suggestion would be great. I'm FREEZING !!!!

 

[Laph]

Sounds like a vacume leak at your controls or, further back.