heater not working

hey,
when i bought my car (a few weeks ago) the slider to adjust the heat was really hard to move, but the heat and air both worked. i pushed the slider too hard trying to losen it, and now it slides good but i have no heat! i freind of mine has a 99 and to told me this is a common prob with 5th gen ludes. has anyone had this prob and fixed it? any tips would be great,

thanx
jimi