Where is the coolant sensor located on a 1997 Isuzu Rodeo V6 3.2"?

My 1997 Isuzu Rodeo is overheating and the coolant fan is not coming on when the vehicle overheats unless I turn on the air conditoner and then it works just fine so my only guess is that is the coolant sensor but I can't seem to find it, and I even bought one of those Haynes Repair Manual but if was of no help to me. I thank anyone for their help please.