is350ajk

I am new to the forum and just picked up a '06 IS350 that came on a trade in, but it came with bit of custom job in audio department. Someone has installed Kenwood DDX516 nav/dvd unit and removed part of the center display ( clock/hazard) . It also had a box, and additional amp in the rear as well which was cut off, when it was traded
For starters, I'd like to fix climate control first which is not working - it does light up (buttons only) but does not function in any way.

Things I tried:
-Got a used climate/radio control but it has not resolved the issue at all.
-Checked fuses (all fuse boxes)

My question is:

1) is cd changer unit required for HVAC to work?
2)If cd changer is not required, which unit controls the HVAC ? Location
3)Will radio unit work with out the CD unit?
4)Any wiring or any other insight anyone can bring.

Thank you

is350ajk

Any suggestions?

is350ajk

Update:
1) Yes CD changer/Radio unit is required to work.
2) - See #1
3) No , CD/Radio unit is required for it to work
4) Other then do not modify the stock unit beyond lexus unit, it is simply a big PITA