1982 Jeep Cherokee no heat

if you can hear the motor(fan) spinning, check the linkage that controls which vents are open, also check for a vacuum leak as the vacuum hoses on a jeep that old go out frequently and many times control the switching for the heater/defrost/ac. your first thing to do will be to grab a manual for this jeep and check the actual location of the heater/vent/ac fan. there is always the chance that the fan slipped off the motor (usually doesn't happen, but the circlips have been known to fail)

have you tried it in any other position? ie: vent or ac