Check if you are getting voltage to the blower motor when it's not working (might be hard to find that moment, and have a volt meter ready lol). If you have a +, but no -, then it is the blower motor resistor. If you have both +, and - then it is the blower motor. If you aren't getting **** then it's either a relay, or a bad connection somewhere; or possibly the actual switch at the climate control panel.