The A/C blower only activates at high speed. What could be the problem ?

blower motor resistor is burnt! replace it.there are FOUR different ones it could be.hope it's Manual temperature control and R56 model,it's the cheapest one $41.99.if it's Automatic temperature control and the R52 model,it's $135.99.if it's Manual temperature control R52 model,it's $59.99.if it's Automatic temperature control R56 model,it's $122.99 at the ZONE.