HVAC Blower motor

I have a 16 cherokee that has the weirdest problem. When the outside temp reaches about 65 F the blower stops working altogether. Sometimes while driving it will just start again an work normal and its possibly due to air moving due to driving. It started this last fall and then when it got cool/cold here in MO it worked all winter. Now its Spring and every warm day it starts acting up. The hotter it gets outside the less it works.

Ideas??? I don't think the resistor is the problem since it works on all speeds when it is working. When it's not working it's dead on every speed.

 

I would say "it is the resistor". Check it for a small crack, should be cheap to purchase a new one and replace yourself - Good Luck