my blower motor only works on high replaced blower resister then blower worked a on all speeds day later worked only on high went back to parts store got another resistor work on all speeds next day only work on high what can i check to see whats bad and how have a service mannal does not troble shoot this problem

 

Just a thought... A motor going bad might pull too much current. But I would've expected the fuse would blow first before damaging the resistor?