I have some oddities with my blower also. When the engine is cold, it only blows on defrost. When the engine is warm, it will only blow on the other settings if I first turn it on with the defrost setting. Once the engine is warm and I shut if off and start it again before the engine cools off, it will run in the other positions without first beginning with the defrost. I suspect it has something to do with the sensor that keeps the blower off until the engine is warm.