Yukon Denali AWD V8-6.2L (2007)
Evaporator Core: Customer Interest
A/C - Musty Odors Emitted From (HVAC) System
Bulletin No.: 99-01-39-004C
Date: June 12, 2009
Subject: Air Conditioning Odor (Install Evaporator Core Dryer Kit and Apply Cooling Coil Coating)
1993-2010 GM Passenger Cars and Trucks (Including Saturn)
2010 and Prior HUMMER H2, H3
All Equipped with Air Conditioning
This bulletin is being revised to add the 2009 and 2010 model years. Please discard Corporate Bulletin Number 99-01-39-004B (Section 01 - HVAC).
Some customers may comment about musty odors emitted from the Heating, Ventilation and Air Conditioning (HVAC) system at vehicle start-up in hot,
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.
If the vehicle is not factory equipped with the imbedded afterblow enable feature, it may be added with the Electronic Evaporator Dryer
Module Kit (P/N 12497910 or AC Delco 15-5876).
When installing the Electronic Evaporator Dryer Module, you MUST use the included electrical splice connectors to ensure a proper splice.
Complete detailed installation instructions and self testing procedures are supplied with the kit. If necessary, the Electronic Evaporator Dryer Module
may be installed underhood if it is protected from extreme heat and water splash areas.
To immediately remove the evaporator core odor on all suspect vehicles, it is necessary to eliminate the microbial growth and prevent its re-occurrence.
To accomplish this, perform the following procedure:
Vehicle and Applicator Tool Preparation
1. The evaporator core must be dry. This may be accomplished by disabling the compressor and running the blower fan on the recirc heat setting for
an extended period of time.
Compressor engagement will cause the evaporator core to remain wet and will prevent full adherence of the Coiling Coil Coating to the evaporator
2. Verify that the air conditioning drain hose is not clogged and place a drain pan beneath the vehicle.