under the dash in the heater assy there is a plug that is connected to a rectangular fitting that is recessed into the housing.There is a sprung fuse in there that is soldered to keep it in contact. If it has been too hot it melts the solder and the fan only gets full power.It is a rheostat and if you are careful you disassemble it and resolder the link.Don't run the fan until the rheostat is put back into the heater housing as it is cooled by the airflow it generates and will overheat and the soldered joint will fail again.If it's not this I don't know of any other cause.Hope this helps.
- posted
19 years ago