I own a 91 Camaro RS and my cooling fan will not come on. I noticed this the other day so I shut the car down. I have since replaced the coolant temp sensor, fan relay (it's the one on the right, isn't it?), and fan switch (the aftermarket Hypertech switch that turns the fans on at 200 and off at 185). I hotwired the fan (apply battery voltage to it) and it comes on. If the car gets hot and then I shut it off, and then have the car KOEO (key on, engine off) the fan won't come on (it used to). The only thing I haven't tried is turning on the AC to see if it works then. I am stumped. Any suggestions?

P.S. What is the sensor on the driver's side cylinder head?

 

The fan will come on when the AC is turned on. Also, I manually tripped the relay (grounded the green+white wire) and the fan works. I am going to rig up a switch like a lot of people do here but I still don't know why the fan won't come on by itself. Any thoughts?