Having trouble diagnosing a cooling/AC problem. AC works (no leaks), and charged. Has main in-line cooling fan (runs w/engine all the time), and smaller electronic cooling fan for AC. Hooked power directly to electric fan and it checks out OK; however, not getting signal or power from sensor to turn on, therefore, not very cold air coming through. Checked fuse and it's not blown either. Checked Haynes manual but dircects me to check the coolant remperature switch. Is this also refered to as the coolant temperature sending unit? Where is this unit located?