Cooling fan problem on 91' 3.1l Need some help

Ok,
So the drivers side cooling fan will not come on at all. I ran 12vdc to it and verified fan motor was good. Then i checked fuses and swapped relays around but nothing. So i checked the sensor at the thermostat housing and it appears to be working correctly.
Now what is the sensor on the side of the radiator? Is it for the tranny fluid temp? Kind of stumped here.....
The passenger side fan works when a/c is on, but i think that is correct. Any input on what i should look for next would be greatly appreciated!!!

Drivers side fan is for when you are running the AC, or if engine gets VERY hot. Passenger side fan for normal cooling.

Sensor on side of radiator is for coolant level..

jumper the relay- see if fan runs-- what makes you think it is not working as designed? overheating? secondary fan comes on when very hot- as a back-up..

Yeah it's overheating after 5 to 10 minutes of just idleing. Gauge goes to 3/4 and stll no fans, so i shut it down to prevent damage.

Drivers side fan is for when you are running the AC, or if engine gets VERY hot. Passenger side fan for normal cooling.
Huh, so any thoughts as to why the passenger side comes on rather than the drivers (when a/c is turned on)?

All GM W-cars wait on a/c head pressure to turn on the fan(s) at 175 psi the primary fan comes on, and at about 250 head the secondary comes on....

What is engine temp when primary comes on? 3/4 on a gage means little... perhaps you don't allow it to get hot enough to run secondary fan..a tech I scan tool wil command fans on.. or by jumping the ALDL connector (as I recall) will energize fans... what happens when you jumper the relays...

you are NOT overheating until you are above 250 or so--or your dash gage is in the red...engines by design can run hotter these days..primary fans usually energize at 227 as viewed on Tech I, and secondarys are probably 235+ or so...

I think there is a good chance your system is okay- you just haven't found out how it works yet...I see this all the time folks driving when it gets warm out- not yet using A/C (no fans) but tell me their engine is overheating because it runs hotter than normal--yet when I hook up to them- and command them on, they work just fine..when they use the a/c, it runs normal, because the fan(s) are on....they have a hard time believing me--I always ask-what their definition of overheating is-- mine is coolant boiling out into the burp tank....they say that doesn't happen-- then I say that is not overheating...