99.9% it's your blower resistors. Dealer is probably $40-60 for the part. Or try e-bay, etc. Usually located on passenger side under glovebox area. The resistors are not visible because they are inside the plenum (heater box) but one or two screws hold a connector with wires coming from the switch. Unplug the connector, remove the screw(s) and work the resistor pack out of the hole. There are many threads with various schemes to make repairs but think you'll find it easier to simply replace the unit.
try a new thermostat, or it could be the heater core. My girlfriend said her car wouldnt get warm, so i checked the anti-freeze and it was bone dry, just something to keep in mind.well lets see if yall can help me. i have a 78 and it blows cold, no heat at any level. the temp guage barely moves off "C", and i checked all the fuses.
not trying to hijack your thread man