I have an Ungar 9911 soldering iron handpiece
without the controller. Looks new.

I thought it would be trivial to build a temperature
controller.
I can make it hot. There is some PTC going on
as the current goes down as the iron heats up.

I expected some feedback.
The only other connector pins that have some
connectivity measure 497 ohms independently of
temperature. Can't use that for temperature monitoring.

Google has failed me.
Anybody know how these work?