1999 Stratus AC, speedometer and tranny problem(s)

1999 Dodge Stratus, 160K miles, 2.4L automatic.
While driving, my speedometer stopped working and after stopping for an intersection, the car wouldn't shift into the high gears. I tried to limp it in, but then the AC stopped working and almost immediately I noticed a lot of grey smoke coming out. I stopped, popped the hood and smelled an almost burning-electronics type of smell. I noticed the smoke seemed to come from the AC and there was oil spewed out around there. A mechanic said the AC compressor was definitely shot but didn't know why the speedometer and tranny would be affected. Are these all parts of the same problem or are they separate, coincidental problems? Thanks for the help.