Red light flashing on air recirculation:88 300E

[kjtar]

Outside ambient air temperature was 44F. Driving home from work, usually takes between 21-30 minutes. Hit temp. button, and noticed a bit later the little red light in the air recirculation toggle switch was flashing. I read the owner's manual and can't understand it. It seemed like the temperature of the heat coming out was warm enough, but the fan never went on. Should I be worried, or just consider this an anomoly until the next time it happens? I have the mechanical aptitude of a half-dead moose, so with that in mind, all replies appreciated.

Thanks!
Tom
Tulsa, OK
'88 300E