low coolant signal (red light and notation) but temp gauge normal.

What is your question?

It comes on when the AC is active,and sometimes when I am going under 30. But sometimes when I am doing 50. I stop, turn off the engine, wait a minute or two when restart. Light almost always disappears. Temp gauge is always dead center. No noises, leaks or strange stuff. 72,000 miles. Well maintained, new coolant about 68,000 miles when thermostat was changed.

What makes this problem better or worse?

Sometimes low speed, like in a neighborhood. Yesterday at 50 mph.