Well, I must apologize my friend.I don't think the info on your car, the model and engine size etc were on the original post but is now.
I didn't provide an answer then as I take the specific model/engine information and first review the TSBs for your specific vehicle. It is possible that others have had the same issue. So the first thing is get your specific vehicle info then right to the TSBs.
Okay after looking through about 200 TSBs there is the one below. But from what you are saying (I think) this isn't the odor.
Air Conditioning Odor (Install Evaporator Core Dryer Kit and Apply Cooling Coil Coating)
TECHNICAL SERVICE BULLETIN
Reference Number(s): 99-01-39-004B, Date of Issue: May 29, 2007
Affected Model(s): 1993-2008 GM Passenger Cars and Trucks (Including Saturn); 2008 and Prior HUMMER H2, H3; All Equipped with Air Conditioning
Supercedes: This bulletin is being revised to update the vehicle applications, model years, correction procedure, parts information and tool numbers. Please discard Corporate Bulletin Number 99-01-39-004A (Section 01 - HVAC).
Related Ref Number(s): 53-12-12A, 99-01-39-004, 99-01-39-004A, 99-01-39-004B
Some customers may comment about musty odors emitted from the Heating, Ventilation and Air Conditioning (HVAC) system at vehicle start-up in hot, humid conditions.
This condition may be caused by condensate build-up on the evaporator core, which does not evaporate by itself in high humidity conditions. The odor may be the result of microbial growth on the evaporator core. When the blower motor fan is turned on, the microbial growth may release an unpleasant musty odor into the passenger compartment.
There are several other possible sources of a musty odor in a vehicle. A common source is a water leak into the interior of the vehicle or foreign material in the HVAC air distribution system. Follow the procedures in SI for identifying and correcting water leaks and air inlet inspection.
The procedure contained in this bulletin is only applicable if the odor source has been determined to be microbial growth on the evaporator core inside the HVAC module.
Many vehicles currently incorporate an afterblow function within the HVAC control module software. The afterblow feature, when enabled, employs the HVAC blower fan to dry the evaporator after vehicle shut down and this function will inhibit microbial growth. Technicians are to confirm that the customer concern is evaporator core odor and that the vehicle has the imbedded afterblow feature, as defined in the SI document for that specific vehicle model, model year and specific HVAC option. Refer to SI for enabling the afterblow function. Vehicles being delivered in areas prone to high humidity conditions may benefit from having the afterblow enabled calibration installed prior to any customer comment.
Try to narrow it down if it is coming from the vents with the AC on or the heater on or the vent on.
Is it there with the AC off also and no blower fan going.
You will have to smell around by the lower dash area etc to try to track down a specific area.
Is the carpet damp on the passenger side under the dash area.
Next, look under the hood all around that side of the engine for anything that may have signs of getting hot and melting. Stuck to the manifold etc.
Look under the car near the exhaust manifold to see if there is something in that area.
If it is coming from the AC area then I would remove the blower fan and see if leaves or anything is stuck in the blower area.
When you run your AC does condensation drip on the ground under your car passenger side?
Let me know what you find out.
Please consider a to help us answer more questions.
Tuesday, September 22nd, 2009 AT 9:26 PM