What would cause the heater to produce heat but not blow air no matter which setting it is on?

There is probably something wrong with the fan motor. It could be the fan motor has a bad switch or connection or the fan motor could be bad. The above Answer might be true in some cause's but before I replaced a fan motor I'd check the fuse first. The blower cage could be dirty. I'd bet it's a resistor or a relay. Usually they are right next to the fan somewhere. The wires split off from the the bundle and go to the fan and the resistor.