What is this on my compresser?

[shakrepg]

On my 97 caravan le 3.3, I replaced the a/c compresser, exp vave and drier, I had some sort of sensor mounted on the compresser, it was square and its 2 wires were wired into the a/c clutch, what is it? I threw it away with the old compresser(duh!), Im getting cold air, but I hear a slight whine when ac is on, and engine rpms go over 1500, any ideas? It is the 2nd compresser to do this in the past 2 weeks. I do residential a/c for a living, so I know the correct procedures used in replacing the compresser, and I did it by the book. Thanks.

[Airjer_]

Sounds like it may have beed the diode to keep power from backfeeding from the compressor, maybe?

[shakrepg]

Well, thanks, maybe (just kidding). Is there any way that eliminating that would cause a whining sound when ac is used, Im on my second compresser this month, because the previous one whined louder.