Without the thermal I would have never found this one today! 2001 American Standard heat pump
I inspected the safety pullout panel and no signs of burned or scorched marks, no loose terminals.
While running the emergency heat, and checking the vents I got 95 deg. with my temp gun. Sufficent working order for emergency heat in this part of the country.
After I shut the unit down I went back out just to look and “Shazam”
Hot enough to fry an egg. 
So how did you report it?
While testing the emergency heat for the upstairs a defect was noted in the fuse disconnect located by the unit in the garage. The wire terminal could be loose or the supplemental heat may be failing and causing excessive amperage draw.
A qualified hvac person needs to further evaluate to determine the source of the problem.
You could measure the amperage draw to verify load. However, the thermal pattern is characteristic of a loose or high resistance connection.
I was hoping that you didn’t mention burning or frying eggs in your reporting:-)
I figured at that temp no need to.
nice
The connection at the pull-out fuse plug is loose.
I bet it is hotter than that, if you had a good focus. 
You can trash that load imbalance of the electric heaters scenario. That condition will only happen about once in fifty years.
good catch