Here is a TSB from GM concerning heat from one vent and cold from another. If I am understanding your question correctly.
File In Section: 01 - HVAC
Bulletin No.: 02-01-39-001
Date: February, 2002
TECHNICAL
Subject:HVAC Temperature Difference Side to Side and/or DTC B0361, B0441 Set (Replace HVAC Controller, Splice into Backlighting Circuit)
Models:1997-99 Buick Century, Regal1998-99 Oldsmobile Intriguewith RPO CJ2
Condition
Some customers may comment on a temperature variation between the left and right hand ducts. Typical concerns may include that the right side of the vehicle cools down but the left stays warm or the opposite. This condition is sometimes associated by the customer with a recent service visit for other non-related repairs. The codes, DTC 80361 or B0441, may be present but will not illuminate a telltale lamp.
Cause
The HVAC controller unit and the TEMP door actuator motors rely on a feedback system that supplies the controller with count values in order to accurately adjust the air temperature. When battery power is interrupted to the HVAC controller, the current actuator position values are lost. When power is restored, the controller will perform a "sweep test" of the doors from full cold to full hot and record the end values for reference. Over time, the TEMP doors may develop some flexing when run to their extremes. This flexing allows the count values to run out of range (beyond 0-255) and results in DTC code 80361 or 80441 to set.
Correction
A revised HVAC controller has been released with new programming that allows for a wider tolerance in the expected range of the TEMP door. Replace the controller using the procedure below:
Important : On the 1997 Buick Century and Regal, additional steps are required. You will have to run a jumper wire to the new HVAC controller. Be sure to follow the additional 1997 model year steps below.
Disconnect the negative battery cable.
Apply the parking brake and block wheels.
The section below includes steps to revise vehicle wiring to enable HVAC controller backlighting.
If the vehicle is a 1997 Buick Century or Regal, refer to the section below titled 1997 Buicks (Enabling Backlighting Circuit).
Additional Steps for 1997 Buicks (Enabling Backlighting Circuit)
Remove the radio retaining bolts.
Auto Service Technician
ASE Master Tech w/ Advance Engine Performance