why do my 2010 Honda fit only blow on high

Hello, The most common reason for this is the blower motor resistor. The resistor is what changes the speed of the fan, and when it goes bad, whichever speeds are affected will not work. They are normally located on the blower motor. Usually behind the glove box or under the passenger dash. Let me know any questions you have, and here is a link if you would like shop recommendations: http://repairpal.com/honda-within-10-miles-of-atlanta-georgia-30349