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Musty Odor from HVAC

Old  February 28th, 2007, 4:51 PM
Musty Odor from HVAC

Here is a little known service proceedure that can stop your Tahoe's HVAC system from getting that musty smell casued by mildew.

Some owners of 2007 full-size utilities and pickups with Automatic and Manual Climate Control (RPO CJ2 , CJ3, or C67) may comment of a musty odor from the Heating, Ventilation and Air Conditioning (HVAC) system. This condition occurs most often on initial startup after the vehicle was driven on a hot, humid day. The condition may be caused by condensation build-up on the evaporator core, which does not evaporate by itself in high humidity conditions.

The 2007 full-size pickup trucks and utilities have an option to enable afterblow on vehicles equipped with Automatic and Manual Climate Control. This is different from previous years, where the only way to prevent repeat A/C evaporator core odor concerns was to install an afterblow module kit.

TIP: Do not enable the afterblow function until its purpose and operation are explained to the customer and they approve the change.

Once the afterblow option has been enabled, the blower motor will turn on approximately 10 minutes after the vehicle is shut off. The blower motor will run continuously for 10 minutes at a 30% duty cycle. The afterblow function will activate only if the air conditioning compressor was engaged during conditions of high ambient temperature. If the vehicle is started within 10 minutes of the last key off, the afterblow function from the previous key cycle will be cancelled.

Turn this option ON in the HVAC Control Module instead of installing the Electronic Evaporator Dryer Module Kit referred to in the Air Conditioning Odor bulletin 99-01-39-004A.

To enable afterblow:

1. Verify the Tech 2 is updated with the latest software.

2. “Build” the vehicle on the Tech 2.

3. Use the following Tech 2 pathing:

Vehicle Control Systems > Select engine > Module Setup > HVAC Control Module > Afterblow Option

4. Follow the on-screen directions.

Old  February 28th, 2007, 5:42 PM
  • CF Senior Member
    Join Date: Nov 2006
    Posts: 401
RE: Musty Odor from HVAC

So this has to be done by the dealer I take it.

Old  February 28th, 2007, 6:49 PM
  • CF Veteran
    Join Date: Dec 2006
    Posts: 1,689
RE: Musty Odor from HVAC

I turn off the a/c part, but let the blower run for about 2-3 minutes before I end my trip. Does this work for drying the ac out before shutting the car off.

Old  February 28th, 2007, 7:06 PM
RE: Musty Odor from HVAC


Is there a way to set the HVAC so that it stays on recirculate? I really get annoyed when I drive and I have the air flow continuously on.

Old  February 28th, 2007, 9:06 PM
RE: Musty Odor from HVAC

ORIGINAL: engine2

I turn off the a/c part, but let the blower run for about 2-3 minutes before I end my trip. Does this work for drying the ac out before shutting the car off.
Your method is actually the preferred; but most people (including myself) don't possess the mental capacity to remember to shut the compressor down several minutes prior to the engine.

And this does have to be accomplished by the dealer but at least you know that it's offered and also what to ask for should this apeal to you, it is a free of charge service.

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