I have repaired a VTS air handler unit commanded by this PDA.
The cable was like this when I found it:

Some trial and error led to the following pinout:

PDA conn:
LCD is upwards
18 pin

pin 1 left
1 green
2 purple - VBAT
3 X
4 Brown
5 X GND
6 BLUE GND
7 X
8 X GND
9
10
11
12
13 black tx
14
15
16
17 VCC
18

Maybe it will be useful for someone.