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.

 

[WalleyeMikeIII]

Add me to the list, my 2022 is starting to stink now...anyone else brought this to the dealer's attention...what was the reaction?
My Cabin AC Filter was changed 5k miles ago...so would think it isn't that...but planning on pulling it tonight to inspect.

 

[WalleyeMikeIII]

Add me to the list, my 2022 is starting to stink now...anyone else brought this to the dealer's attention...what was the reaction?
My Cabin AC Filter was changed 5k miles ago...so would think it isn't that...but planning on pulling it tonight to inspect.

Called dealer today, they are going to take it Monday, diagnose and fix...at least that was their promise. Even offered me a Loaner to drive! Will report back when I am done w/ the service.

Did read this online today re: Afterblow function on the trucks..

HVAC After Blow Function

There should be other topics similar to this here. But I thought it shouldn't be a bad idea to share copy of my technician's report and the article related to HVAC's After Blow function. My previous 2014 Silverado LT had this function enabled by default, but the new generation needs to be activat...

www.gm-trucks.com

I am going to ask them to enable if possible.

 

[WalleyeMikeIII]

I have noted that the smell had subsided somewhat from when I last posted. Still humid as ever here this summer, so I don't think a lowering in humidity had anything to do with the change.

Vehicle in at dealer yesterday, they:
- Enabled afterblow
- Changed my cabin air filter (said I need to use the one with Carbon in it, but installed one without, because they were out of them with carbon) even though I just had it changed 5000 miles ago. I asked for the old one back, it looked like new, I sniffed it, it had no smell.
- With my permission, set off an "odor bomb" in my vehicle, and now it smells fresh and clean (essentially some sort of ozone air freshener).

Charged me $20 for the odor bomb and $30 for the cabin filter, and $20 labor...hopefully with afterblow on, this cures it. Provided a 2025 2.4 Turbomax Sierra 1500 for me to drive for the day.

There is water dripping on my garage floor under the area of the front and rear condensate drains, so no evidence of them being plugged.

 

[Marky Dissod]

This stuff came out AFTER I gave up being a livery driver / chauffeur:

Pooph® - The Pet Odor Remover That Takes STINK Out of the Equation

Pooph® takes “stink” out of the equation – completely and permanently dismantling odors on a molecular level. It works instantly to eliminate odors at the source – so there is no stink OR fragrance... when you use Pooph®, it’s as if the odor was never there! Pooph® is safe for people, pets and...

www.pooph.com

Used to spray about 3 seconds of Lysol or other air deodorizers into the cowl under the wipers daily.
Never had any issues with interior stink.
Even though I mostly no longer drive others around for a living, I'm DEFINITELY going to try this stuff.

 

[Fless]

When I run the A/C I always turn off the cooling a few blocks before home, but leave the fan on to help dry the evaporator. Guess that could be called beforeblow. That helps clean off some, if not all, of the condensation that's causing the odor.