I'm sorry. Twice.
Once for already posting about four questions this week.
Second for not being able to find this using the search
tool. (I LOVE this forum--couldn't live without it--but I'm
thinking the search tool is not the best.)

This question will help TWO people. My brother has
been in HVAC for 12 years, learned on the job. I've
been in HVAC since 2008, (started tech school then,
but given the deep recession, the time spent has not
been quality time, much more DOWN time).
He currently has an outside unit control board with an
OAT (outside air temp) fault code. We at least have
determined that the thing is a thermistor, not off/on.
I have less of a problem. I noticed, on a dead
compressor service call, a dangling wire --stripped
but not connected, ran back to outside unit's control board,
and wiring diagram says there might have been at one time
an outside air temperature sensor. My unit is running fine,
without the OAT. And at the homeowner's request, I have
disabled the heat strips at the thermostat. I can have a
relaxing weekend. No 2 am insomnia wondering if I've done
something wrong.

I thought I remembered, from reading long ago, such a
sensor being for the indoor control, to let it know when
heat strips might want to be added, but I have a very
bad memory and I can't find any info easily.
That's why I'm here.
And that purpose seems fairly innocuous to be giving
an outside control board a crippling fault code. On the
other hand, HVAC units never have mere warning codes, huh?
That leaves me to conclude that my memory is wrong, that
the sensor has some more important purpose.

One more thing. My brother and I were joking around today
about our time in HVAC and our knowledge levels. (All in good
fun--I ask his opinion ALL of the time.) So for you folks kindly
being helpful and responding, could you also throw in how long
you have been in the trade?

Thank you.