1989 Dynasty overheats, no radiator fan

1989 Dodge Dynasty LE overheats unless the A/C unit is ON. Radiator electric fan does not turn ON unless A/C is turned ON.

The ON position of A/C automatically sends an electrical signal to the electric radiator fan to start. I can verify signal with 12v test light.
If A/C is not turned ON, then no radiator fan, then engine temperature gauge gets extremely hot.

Highway driving allows sufficient air flow over radiator to cool the liquid engine coolant.
At city / local roads, red lights, stuck in traffic, engine temperature soars to HOT.
Why is electric fan not getting signal to turn ON?
Electric radiator fan used to turn on after engine was turned off until engine would cool. This no longer occurs.
What happened?
Radiator Fan Relay is located on driver side engine bay fender. It passes 12v to radiator fan only when A/C is ON.