Classic/Antique Car Repair: 90 firebird cooling fan, engine management computer, electric cooling fan

Question
My 1990 firebird operates the cooling fan when the a/c pressure switch activates but not when the a/c is off.  Where might I look for the problem?

Answer
The electric cooling fan is controlled by the engine management computer. It gets information from the coolant sensors and turns the fan on when the engine temperature reaches between 212 and 220 degrees F. And then shuts the fan off when the temperature drops to near 200 degrees F. So unless you really get the engine warm the fan will not come on when the A/C is off.
Brad