HVAC mildew smell

[d0wnShifT]

Been noticing the past month that the HVAC when first turned smells like mildew for the first 5 minutes. I live in a humid climate but have never experienced this especially after one year. Taking it in soon for other things and will have this addressed as well.

 

[Micahsd]

I haven’t experienced that in my ‘21 Tahoe yet but I did learn on my old ‘17 Acadia to never leave the HVAC controls set to recirculate. Pretty sure that’s what caused it on that vehicle so I’d taken the same stance on the Tahoe and just leave it set to Auto all the time and let it control the recirculation.

At the time I thought it was a good idea but I guess it can build up moisture by doing that and cause that smell…I ended up using some BG Frigi-Clean and sprayed it into the air intake for the HVAC (on the Acadia it was near the under hood section on passenger side near the wiper, but I don’t know where it’s at on these vehicles).

 

[gooffeyguy]

On the 07-14 models there was a service bulletin that came out to deal with vehicles that may have this problem. The dealer could enable the afterblow feature on the hvac modual which would cause the blower to turn on for a few minutes about 30 minutes after the vehicle was shut off. This helped dry up any condensation in the evaporator and surrounding ductwork in the dash and keep that mildew smell from forming.

 

[swathdiver]

Been noticing the past month that the HVAC when first turned smells like mildew for the first 5 minutes. I live in a humid climate but have never experienced this especially after one year. Taking it in soon for other things and will have this addressed as well.

On the 07-14 models there was a service bulletin that came out to deal with vehicles that may have this problem. The dealer could enable the afterblow feature on the hvac modual which would cause the blower to turn on for a few minutes about 30 minutes after the vehicle was shut off. This helped dry up any condensation in the evaporator and surrounding ductwork in the dash and keep that mildew smell from forming.

Yep, Afterblow basically turns the fans on and dries out the evaporators. You can do this manually by turning off the compressor and running the fan on high for a few minutes before shut down. I wouldn't do that either! I have Afterblow enabled and even catch it running once in a while. It only runs when certain conditions are met so you are not likely to see it in operation if they activate it for you.

 

[GreenTahoeZ71]

Lubegard 96030 Kool-It Evaporator and Heater Foam Cleaner https://a.co/d/0NXPpEe

I know this thread is old. But this is the solution to this moldy, smelly vent problem and compressor failure due to oil loss from liquid slugging caused by a dirty coil. It is also a cause of blower motor resistor failure and blower failure.

If you have never cleaned the coil in it, then I would get the small can and one of these big cans
Frost King ACF19 Foam Coil Cleaner, 19Oz, 19 Ounce https://a.co/d/j7ipI5e

The spray cap and hose from the little can fits the big one.

Put the little can in first, then the big one, let it sit for the time it says then follow the instructions on the little can about running your air to rinse the coil.

It makes it smell and work better.

Don't forget to rinse the condenser coil from engine side out as well for peak operation.

Hope this helps anyone else that finds their way to this thread like I did.