More than likely, you have a blend actuator(left side) that overtraveled and defaulted. If you could plug a scan tool in it that would read that info, you might see a code B0414, and also see the actuator counts to diagnose. It could need the actuator, or the HVAC head reprogrammed. I would opt to have the reprogram first.
There is potentially a bulletin that applies, here it is.
#PIT3655C: Poor A/C Performance/Recirculation Inoperative/DTC B0229, B0414, B0424 or B3770 - keywords door heater HVAC program - (May 11, 2006)
Subject: Poor A/C Performance/Recirculation Inoperative/DTC B0229, B0414, B0424, or B3770
Models: 2004-2006 Hummer H2
This PI is being updated to remove models because bulletin 06-01-38-003 was released for certain models and to advise the Hummer H2 calibrations are now available. Please discard PIT3655B.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern: Owners may comment on poor a/c performance or that the recirculation mode is inoperative. When checking DTCs, a B0229 will be set in the HVAC control module. When this concern happens, the recirculation door is defaulted to the fresh air mode and the recirculation door counts will be less than 5.
New HVAC control head calibrations have been released to correct all over travel/out of range DTCs (B0229, B0414, B0424, or B3770).
Recommendation/Instructions: To correct this concern, reprogram the HVAC control head with an updated calibrations. This new service calibration was released with TIS satellite data update version 5.0 available May 1, 2006. As always, make sure your Tech 2 is updated with the latest software version.
Important: After reprogramming the HVAC control head, shut the ignition key off for 1 minute or the calibrations will not take.
Please follow this diagnostic or repair 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.
Monday, January 18th, 2010 AT 10:27 PM