A/C compressor clutch - odd running habit

My friend has a 91 s-10 blazer 4.3L. When the blower is on, regardless whether the a/c is on or not, the a/c compressor clutch constantly engages and disengages. I have never seen or heard this occur in any other vehicle. Is this a quirk of the system, or is something wrong here?

Normal operation if its in defrost mode.