Most definitely the blower resistor,very common problem.The new one you get will look different than the original,they changed designs a few years ago.
I had the exact same problem a couple weeks ago. It was the resistor, located inside cabin, passenger side under glove box. It is next to where the passengers right foot would be. You can see the connector harness. I got mine from a junk yard for cheap.
I posted a thread on this in the 'General SR-20' section a couple weeks ago when I had the problem. Check it out.