1990 geo prizm heater problems

I am having a problem with my heater blower. I tested the blower at a reputable parts store, and it works, but I cannot get it to function in the vehicle. I checked the fuses, and visually they are fine, but I don't want to buy a switch or a relay unless necessary. Help! What other problem could this be if the blower works fine?

without more info I would guess the switch. just a guess

it is a common problem in the 90 prism, change the fan speed switch in the dash and you'll have heat again