This is scary. I would bet, especially since you mention your AC went out, the input wires to your blower final stage over heated and caused the fire. The wires on mine over heated, destroyed themselves. FOrtunately didnt' casue a fire since once it went out I repaired it, but they were burnt to a crisp. Check out the images below.
wires completely charred (this is input to final stage):
https://lh4.googleusercontent.com/-z...o/IMG_3371.jpg
final stage itself charred:
https://lh6.googleusercontent.com/-Y...o/IMG_2906.jpg
the old socket melted:
https://lh4.googleusercontent.com/-F...o/IMG_3409.jpg
Funny thing is these wires are hot even when the fan is turned off. I wouldn't be surprised if this is what caused your fire. All of this is located behind and under the fuse box right beside the main junction box