Turning the A/C on should activate your low speed fan. It will also activate during KOER tests and of course when engine reaches the preprogrammed temperature of about 220 degrees.
If your low speed fan is not functioning and other components such as the motor or wiring have been eliminated, its possible your IRCM is not functioning correctly. The Integrated Relay Control Module is located behind the passenger side headlight, it is a black box mounted vertically.