Another A/C question. Must be that time of year

I am trying to help a friend fix the A/C problem she is having.

She owns a 2001 Ford Taurus SE. The heater works fine, but when the system is on cool there is only warm air coming out. The coolant level is in the good range.

The fuses are all good. The engine fan is running. I am at a lose at this point.

Jeff