97 3.8l blew fuse #21

1997 GL 3.8L. While driving, the airbag light on my dash lit up and stayed on. At the same time, my heater/AC stopped working (not blowing). I later discovered that my rear defrosters are offline too. I don't think that it is airbag related...horn and cruise control still work. I checked fuse 36, 39, & 21. 36 and 39 were okay, but 21 was blown. I replaced my front blower speed switch, the heater potentiometer, the selector switch (vent, defrost, etc.), and the relay switch for the auxilary blower motor. The front blower motor resistor looks rusty, but looks like it works okay (continuity). Afterward, I put a new fuse in and it blew within about 20 seconds. With the selector swithces set in the off position, the fuse will not blow. I suspect that the front blower motor relay might be shorted, but I'll be damned if I can find where it is located. Autozone has a diagram of my fuse box, but the socket on my van where the relay is supposed to be located is empty. Can anyone give me some suggestions about how I should proceed?