My 1994 945TG (turbo wagon) has started an odd habit. Every few months one,
two, or all three bolts securing the AC compressor to the mounting bracket
come loose. As you recall, there are 3 bolts: one long bolt for adding
tension to the v-belt, a second for securing the tension bolt, and a third
toward the back of the compressor to help hold things together.

Things will be fine for a while, then the belt will squeal and when I check
it one or more bolts are loose.

Two months ago I changed all three bolts and nuts and brackets, when the
second bolt broke in two!  Afterward I first adjusted the tensioning bolt,
then tightened the second bolt holding the first, then tightened the third.
Yesterday the belt squealed and I found that bolts #2 and #3 were tight, but
the tensioning bolt had backed out a few inches.

What gives? Any suggestions? Is there a better or preferred method of
tightening the bolts?

The AC compressor seems fine, makes no noise, and the A/C is very cold. I
just can't keep the bolts tight.

Odd, very odd.