Chevrolet Repair: What component does this ?, haynes manual, compressor clutch

Question
hello bsb --

i've got a 1987 Chevy R20 with 350ci (5.7 l) and
i'm wondering what control component does this.

normally, when in drive and stopped (like
when waiting at macdonald's window) i can a
small distinct click and the idle speed will
increase slightly.  5 - 10 seconds later,
another click and a slight decrease in
idle speed.  this is when i have either the
heater or a/c on.  i think i heard someone
say that the computer was adjusting to
engine load.  what component am i hearing ??

the reason i ask, is that now, instead of
a nice distinct click, i hear a kinda
rattle (maybe call it a growl).  the engine
is still running fine, but i want to catch
this before i go on a long drive to go
hunting.

from browsing through my haynes manual, i would
guess the IAC ... does that sound reasonable ?

suggest a method to confirm and/or test ?
is it actuator or sensor, you think ??

thanks,
patrick

by the way, cool concept for a website.  

Answer
What you are hearing click in and out is the A/C compressor clutch.  The frequent clicking in and out means the freon is low and cannot keep the system engaged.  The idle speed changes because the compressor puts a load on the engine and the computer senses that the compressor is on and bumps up idle speed.