OK, so...
Thanks to Febi we have the guide in pdf format in the Reference section.
Page 0670-12 shows that 19 controls the Interior Lights Timer, the Dual Temperature Switch, the mirror control switch, and the AC Compressor Control Unit.
If you go to page 6454-0, you can see the dual temp switch.
6330-0 shows the interior lights - does yours have the timer unit? Mine does not, so this page doesn't apply to mine...
And, 6452-0 shows the AC compressor...
Like I said, I'd start with the wiring under the hood, so all the AC stuff first. Check for shorts/ breaks/ burned insulation, continuity, all that.