'95 S320 Climate Control Diagnosis
 

:confused: Repair/Maintenance History: Installed blower resister(no high speed - corrected), cabin filter, overhead sampling motor recently replaced (cheap attempts to fix problem). Miles approx 125k.
Problem: When ambient air reaches a point where AC is called for, driver gets AC, passenger(spouse) gets high heat - through the dash main vents. Occasional squealing noise can be heard under the dash near the glove box (not spouse).
Unfortunately weather is not conducive to problem duplication at this moment. All other functions seem to be working correctly.
Question: Where can I find, easy to understand for a septuagenarian, steps to diagnose the system? Understand that the climate control buttons are used for diagnosis?