Complicated Sorting Data Problem

Hello everyone,

I am trying to sort a list of temperatures to analyze a chillers operation.
The chiller turns on when the outside air temperature is 80, and turns off
when the outside air temperature is 70. I am trying to find the time when
the chiller is on (temperature was above 80 and didn't drop below 70) and the
temperature is between 70 and 75. All I need is excel to display a 1 if it
is on (and between 70-75) or 0 if off, because every 1 is a unit of time.

All the sorts I have tried are unable to look back and see if it was turned
on, because it may have been above 80 twenty cells ago and now is in the mid
70's.

Any help would be great thanks in advance.

Jim