how do I troubleshoot overheating problem?

Hello, a girlfriend of mine has a '95 beretta, v-6, auto, A/C that occaisionally overheats. The problem is very intermittent- it has only overheated 4-5 times in the past 6 to 8 months. Can anyone explain the steps to checking the cooling system? Besides the normal things like a loose belt on the water pump, a unblocked radiator, and a working thermostadt, I heard there is a temp. sensing unit of some kind that controls the cooling fan. I'd appreciate any info.
Thanks:licka:

the fans should kick on at 220-230 degrees, and a cooling system pressure test will rule out a bad intake gasket or blown head gasket.

have you tried bleeding the air out? they have I think a 7mm bolt on the top of the water pump that you can bleed the air out... be careful it breaks easily only needs a small twist to tighten it not very much at all