I did a search and found several threads that mention something similar to this problem, but no one came back and posted the fix.

The cooling fan will come on when forced by turning on the AC, so I know the relay and fan are good. With ignition turned on, I can jump across the temp switch, but the fan does not come on, however once I turn the switch off it runs with the jumper in place. I have checked for air by bleeding the system. Could this be caused by the timer relay that I have seen mentioned in several threads? Also, as of late, I have noticed that the fan does not come on after shutdown like it used to.