Update: I replaced the relay and now, when the high speed fan turns on, the air stays cold and the fan keeps cycling on and off as normal. HOWEVER, in order to get the fan to turn on in the first place, the car has to be at idle for nearly ten minutes. I let it sit in the driveway on a hot day and it kept the air cool, but I was stuck waiting for a train to pass and the fan never kicked on, so the air gradually got warmer and warmer until it became uncomfortable. On many cars, I hear the fan turn onto high far more frequently, and I want to know why mine is being so conservative with the fan.