[V8] Electric Cooling Fan

[Thomas Barbera]

Fellow v8 fans,
Just yesterday I discovered issues with my electric
cooling fan.  It doesn't seem to work at all.  It will
come on if I apply 12 volts to it, but won't come on
when hot or when the A/C is turned on.  I checked the
fusible link, it tests ok. I replaced the 1st speed
relay with a known good one, didn't work.  No power to
the relay.  If I disconnect both temp sensors, fan
does not come on.  

My question is, does the chip in the IC regulate the
fan for high temps only or does it also tell the fan
to come on when the A/C is turned on?  The chip in the
IC is what I suspect.  Thanks in advance.

Tom B. 
'91 V8