Here's the dilema, this HVAC (heating ventillation and air conditioning) system is fully automatic, and has self-diagnostic capabilities. In fact to correctly pinpoint a temperature differential problem, the HVAC module needs to be hooked up to factory software and the information downloaded. The data can be read, and all the blend doors and motors are tested thru the scan tool. If there is a temperatur malfunction, the system has most likely already set a pertaining diagnostic code in memory. This vehicle will at least need to have the codes scanned before you can go further. At this milage there isn't any common failures with the driver and passenger temp control, it might be even as simple as reprogramming the HVAC module, it could have lost it's programming and now is incorrectly calculating temperature on that side. Since you've removed the dash and are taking temperature readings, it's possible that there may be a restriction in the evaporator, or expansion valve, causing the a/c to inssuficiently cool on that side,but I havn't seen this condition, for a vehicle with such low miles.

-Rip