might be your blower motor going bad. The previous owner of mine kept having that problem, so in a pinch her boyfriend stuck a piece of metal in the fuse block to give her some heat. Well, I got to replace the wiring/ controller/ resistor/ and motor when I got it! The motor was super easy to replace compared to most I have done, it's right in the firewall in the engine compartment. I just had to remove the washer fluid bottle to get to mine.