Uhhhhh.... but like, uhhhh what's broken though?
?
What I understand is that they worked fine... then somebody tore the dash apart for instruments removal/installation... then after everything in dash was back together, you discovered the heater cables are "frozen"... which I take to mean they won't budge.
Please don't tell me your highly skilled, compassionate mechanic did the dash instruments removal/installation.
How 'bout undoing the dash again to see what might not be letting things move... and if only if necessary get down to the ventilator box. If the cables are still hooked up properly, then there's always the simple possibility that a good dousing with graphite will work to free them up.
I just have trouble understanding how something down-under can be broken when the dash instruments were out. I can understand them sticking... getting some rust or something so they won't move now, but how anything actually broke so that they require replacement is beyond me with what you've described.
1. if the primary heater slide doesn't move (the one that opens and closes the heater valve --- check the heater valve... most likely culprit or the linkages to it are frozen or not installed correctly.
2. if the passenger side heater vent isn't moving, reach under into the ventilator opening at the bottom and find out whether the flap can be moved... it may be snagged/interfering on the housing... either that or the cable's stuck ... and moving the flap by hand can unfree it.
I presume the air flow controls are working... I would be interesting if the air control cable isn't working though.... since that's got nothing to do with the heater contols.
Almost sounds like a couple of cables are jammed or kinked by misrouting to the ventilator flaps.
Sorry if I sound skeptical about your needing parts costing $1.8k without knowing what's broken on them in the 1st place. You must know more than you've posted.
Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport