Other causes could be a lack of refrigerant, since the drivers outlets are furthest from the evap it allows for them to become warmer. Also a fault within the system, skewed duct temp sensor, or faulty blend door actuator, perhaps. I did find a preliminary bulletin that may have some relevance.
#PIC3097: 98-05 W Cars: HVAC Side-to-Side Temperature Difference - kw AC A/C charge control driver duct heat heater low outlet passenger performance - (Aug 18, 2004)
Subject: 1998 - 2005 W Cars HVAC Side to Side Temperature Difference
The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.
HVAC duct temperatures may be different on the driver and passenger side.
Engineering documentation supports the follow GUIDELINES when diagnosing this complaint:
HVAC in A/C temperature linearity (side-to-side temp difference) should be within 4 degrees in vent mode.
HVAC in heat temperature linearity should be within 7 degrees from floor vent (driver side is usually the warmer of the two)
Front to rear heat outlet duct temperature linearity should be within 11 degrees.
All the above situations are taken from a basepoint of 0 degrees F at 30 mph full blower. So, this information is a GUIDELINE only. NOTE: If the HVAC is in the A/C mode and duct temperature side to side difference is out of specification, the most common cause is a low refrigerant level.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.
(1998 - 2004 Buick Regal/Century) and (2000 - 2005 Chevrolet Monte Carlo/Impala) and (1998-2002 Oldsmobile Intrigue) and (1998 - 2005 Pontiac Grand Prix)
Friday, May 27th, 2011 AT 3:39 PM