# How to Avoid the Dreaded A/C Mold/Mildew Smell



## rcclockman (Jan 16, 2012)

I have heard from some car guys that the best way to avoid this is to never run in recirculate mode and always run fresh air inside... This is what I have always done on my 2000 Silverado and it it has 213,000 mildew free miles, but the Cruze seems to get the mildew smell more from fresh air on then in recirculate, maybe i'm wrong, what do you guys think?? My 2012 eco had the Mildew smell even after Dealer service/afterblow on didn't help, just trying to keep the smell from entering my pristine 2012 Ltz...


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## jblackburn (Apr 14, 2012)

The LTZ auto climate control pretty much does what it wants to control in-car humidity. It would not surprise me if it's running the AC in the winter and/or recirculate mode at times.


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## obermd (Mar 3, 2012)

It doesn't matter if you run recirc or fresh air. It only takes a little mold/mildew to get the process started and once started the only way to get rid of it is to fumigate the HVAC ducting. Also, the dealership should turn on the HVAC after-blow to dry the ducting after you turn off the car.


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## jblackburn (Apr 14, 2012)

> It doesn't matter if you run recirc or fresh air.


The OP is right - generally keeping it in recirculate mildews it up much more quickly. Running fresh air on most cars and turning off the AC to dry out the core ~2-5 minutes before shutting down the car will help keep it from forming on a soggy evaporator core that's just sitting around without airflow.

There are cans of foamy stuff you can spray up the drain hose under the car to clean off the cores - I think I'll have to do it to both cars in the spring. They're both ~2 years old and both have a little funky smell on defrost.


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## 70AARCUDA (Nov 14, 2010)

jblackburn said:


> The OP is right - generally keeping it in recirculate mildews it up much more quickly. Running fresh air on most cars and turning off the AC to dry out the core ~2-5 minutes before shutting down the car will help keep it from forming on a soggy evaporator core that's just sitting around without airflow.
> 
> There are cans of foamy stuff you can spray up the drain hose under the car to clean off the cores - I think I'll have to do it to both cars in the spring. They're both ~2 years old and both have a little *funky smell *on defrost.


I just accuse my wife of having stinky feet (wink,wink)!


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## brian v (Dec 25, 2011)

Stinker Stinker , now you really know what is smelling up yer brand new car .


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## Robby (Mar 1, 2013)

I believe if you run the A/C temp dial to maximum mode the car goes into recirculate without lighting the recirc lamp.

So, once at a decent level of temp I rotate it back.....you can feel a detent btw, and leave it there......I'm confident this is the case cause the fan quiets down as it it begins to pull outside only air.

And definitly get the afterblow enabled if you havent yet.....kind of weird the way it works/cycles/times on/off several times over a one hour period.

Rob


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## McNeo (Dec 17, 2013)

The best thing I've heard to do, whether you use recirculated air or not, is to shut off the A/C and let ambient air run through the system a few minutes before parking. I usually shut my A/C off when I'm at the end of the block on my home and never had a mildew smell in any cars.


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## Merc6 (Jun 8, 2013)

Robby said:


> I believe if you run the A/C temp dial to maximum mode the car goes into recirculate without lighting the recirc lamp.
> 
> So, once at a decent level of temp I rotate it back.....you can feel a detent btw, and leave it there......I'm confident this is the case cause the fan quiets down as it it begins to pull outside only air.
> 
> ...


I also have reason to believe A/C is on(in warmer temps where the compressor is not locked out) when you hit defrost button but does not light up or show up on the touch screen.

As for recirc, it still lets in outside air just not as much as regular mode.


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## NickD (Dec 10, 2011)

If you park your vehicle with a soaking wet evaporator in particular in a warm climate climate, nature will take over for developing mold. Not a new problem, started way back in the 50's when AC first became popular. Was a 1939 Packard as the very first vehicle that had AC.

Only way to prevent this is to switch the compressor off, my rule is about five minutes to leave the blower motor run at full blast before parking your vehicle. And have been doing this in the early 60's without any mold problems.

But mold problems is just the start of your problems, will also have corrosion problems. $$$$$ is the only result of these.

When automatic climate control first came out in around the early 60's, did not have a so called "Econ" mode, all it would do is switch off the compressor. So on these, mounted a rocker switch under the lower dash in series with the compressor clutch solenoid so I could switch it off. Didn't have to do with when they finally added on the Econ switch.

GM is very well aware of this problem, on just a hand full of vehicles, added a timer to keep the blower motor running for about five minutes after the ignition was switched off.

What is really downright stupid is switching on the AC with Defrost, at these colder temperatures, the moisture is very low, and switching on the compressor with a very cold compressor seal that is stiff, so you would lose refrigerant. Idiots that designed the Cruze did this exact same thing, even though they added a compressor switch. You can see that green light come on, but only when the ambient temperature is above about 34*F.

Not quite as bad with the V-5 compressor as it runs all the time, but when the cycling system was used, another POS, compressor would cycle on and off continuously accelerating from zero to the engine speed putting huge unnecessary stress on the belt drive system wearing it out with very little affect on defrosting your windshield.

On previous vehicles using a real mode switch, could cut the wire off that runs the compressor, but can't do this on the Cruze without having the source code on the BCM. So I just crack open a window the defrost the windshield almost instantly. Below 34*F, no problem, a thermistor keeps the compressor off. 

Yet another problem finally solved with the Cruze is adding a cabin filter. Would describe the squirrel cage blower wheel as a leaf chopper that would pile up debris on the face of the evaporator and plug the drain hose. In these cases, the evaporator is sitting in a pool of water. Normally just removing the blower motor would give access to the evaporator so you could clean it out.

Slightly off topic, but can have the same exact problem with the HVAC system in your home, when the AC kicks off, so does the blower leaving the evaporator soaking wet for mold buildup. Solved this by modifying the furnace so the blower is always running at a low speed. Not only prevents mold buildup on the evaporator, but the entire house as well. Did this back in 1965 with my first HVAC system installation. With my newest furnace, low speed was running too high, so designed a motor control circuit to slow it down. Also keeps your home with a much fresher odor.

This is what is called common sense, that is becoming rare nowadays. And since that motor is always running, its the start up that really wears them out. Still kept my 30 year old blower motor, and still runs and looks like new.


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## Robby (Mar 1, 2013)

Merc6 said:


> I also have reason to believe A/C is on(in warmer temps where the compressor is not locked out) when you hit defrost button but does not light up or show up on the touch screen.
> 
> As for recirc, it still lets in outside air just not as much as regular mode.


You are correct......the compressor will run in the defrost position with no lamp illuminated......this is so the humidity is drawn out of the air before it enters the cabin.
Nothing specific to the Cruze.....for the most part the way its been done for over twenty years.

Rob


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## nike12000 (Sep 13, 2013)

Robby said:


> I believe if you run the A/C temp dial to maximum mode the car goes into recirculate without lighting the recirc lamp.
> 
> So, once at a decent level of temp I rotate it back.....you can feel a detent btw, and leave it there......I'm confident this is the case cause the fan quiets down as it it begins to pull outside only air.
> 
> ...



what exactly is the afterblow and whats needed to toggle this on or off?


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## obermd (Mar 3, 2012)

Afterblow turns the HVAC blower on and off after you turn the car off. It starts about 15 minutes after shutdown and continues for about an hour. There is BCM flag that needs to be set to turn it on. It makes the whine many of us hear after turning our cars off sound like nothing. Afterblow is loud. It can also drain your battery so if your car spends a lot of time driving very short distances you don't want to turn it on.


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## nike12000 (Sep 13, 2013)

i do mostly city short trips so good to know is there a way to prevent the smell for someone like me who cant turn that on?


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## obermd (Mar 3, 2012)

Define short. If the engine reached temperature you're probably ok with the power drain from after blow.


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## nike12000 (Sep 13, 2013)

obermd said:


> Define short. If the engine reached temperature you're probably ok with the power drain from after blow.




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I live about 5 min from work


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## Robby (Mar 1, 2013)

I don't think 5 minutes is enouph running time for the afterblow to be enabled......

I don't have the update......actually, don't remember where I placed it.....but memory says A/C run time had to exceed 15 minutes before afterblow would cycle after shutoff.......for some reason, I think I posted it.

Rob


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## nike12000 (Sep 13, 2013)

I have the ltz but I turn off the ac in the winter even tho on auto mode it turns out on should only be an issue in the summer when I want ac tho right

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## Robby (Mar 1, 2013)

The moisture only forms on the evaporator core in warm humid weather......winter A/C operation will not make mold cause the evap isn't wet.

Rob


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## nike12000 (Sep 13, 2013)

Robby said:


> The moisture only forms on the evaporator core in warm humid weather......winter A/C operation will not make mold cause the evap isn't wet.
> 
> Rob




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Right and since I use the compressor in the summer I should not get the smell either right


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## nike12000 (Sep 13, 2013)

I just don't want a stinky car 

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## Robby (Mar 1, 2013)

If your trip is only five minutes odds are the core won't get too damp.......myself, short trip or not, I'd be inclined to still get the afterblow enabled.

btw.....I don't think anyone wants a stinky car heh heh.

Rob


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## 70AARCUDA (Nov 14, 2010)

Robby said:


> ...I don't think anyone wants a *stinky car *heh heh.
> 
> Rob


Just consider it _*toe cologne *_to "mask" the *coolant* odor (wink,wink).


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## Robby (Mar 1, 2013)

Yechhhh!

Rob


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## nike12000 (Sep 13, 2013)

Sent from AutoGuide.com Free App

Cool thanks guys


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## NickD (Dec 10, 2011)

Ha, never switch on the AC when driving in town, won't kill me, and just wearing it out. Should I get a portable AC unit I can strap to my back when walking out to the mail box, cutting my grass, walking my dog, or biking? Just sitting there in the car and not really doing much of anything with power brakes and steering. Then always a breeze when the car is rolling.

Can recall doing a 25 mile forced march in 98 degree weather with a 65 pound backpack on and a very hot hat and uniform on. Heaven was sitting down under a shade tree, back pack off, and getting a sip of water from my canteen. Its all relative.

Now with my wife and grandkids in the car, that is when the AC gets switched on.


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## obermd (Mar 3, 2012)

70AARCUDA said:


> Just consider it _*toe cologne *_to "mask" the *coolant* odor (wink,wink).


Been there, done that.  The mold/mildew smell masks the HVAC ducting glycol odor extremely well.


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## jalaner (Dec 28, 2013)

My job requires evaluation of mold problems in buildings so I have some formal training on the subject. Mold requires both moisture and a nutrient rich substrate to proliferate. The plastic and metal construction of a clean car HVAC would not support much mold growth. The most common mold substrate is cellulose so it is important to exclude cellulose rich materials such as leaf litter from entering the HVAC. Leaves can accumulate on the cabin filter and drop into the HVAC system when service technicians check the cabin air filter. I have had this happen with my Pontiac Vibe. Dust that is drawn into the HVAC from the interior of the car could also accumulate and support mold growth so its important to vacuum the interior regularly. A properly installed cabin air filter should minimize dust accumulation from outside. HVAC recirculation would increase the odor from existing mold because there is less clean outside air to dilute the odor but I don't think it would cause the problem. Recirculation actually reduces the dehumidification load on the HVAC and should reduce the moisture in the system. Operation in fan only mode before shutdown of the vehicle may dry out the system if the humidity is low but would not help much when the humidity is high. Fumigation may temporarily kill the mold but it will regrow if the mold growth medium is not removed. Of course, all HVAC drains should be clear. The best prevention is probably a garage.


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## gransportguy (Mar 9, 2017)

I have found that the smell is sometimes caused from the soap used in drive through car washes. That stuff gets down in the vent system and just stays there and eventually starts to stink. I have found this on rental cars that only have a few thousand miles, they go through the car wash sometimes several times a week. My 2005 uplander has 218000 miles on it, has almost never through a drive through car wash and has no odor.


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## NickD (Dec 10, 2011)

R-134a high side pressure drops to about 35 psi at 40*F, completely worthless to switch on that AC with defrost at these temperatures. Besides that PAG oil, women's facial cream is very stiff at these temperatures as is the compressor neoprene seal. All you are doing is wearing the darn thing out, really doesn't remove any moisture.

With other vehicles even mounted a switch in series with that AC compressor clutch coil, didn't do this with the Cruze, just cracked opened the driver's window to prevent fogging the windows, we are the culprits of this.

Was not a problem with Japanese made vehicles, 88 Supra is like this, when that AC switch is off, its off regardless if you hit defrost or not. Not sure about what the thinking is behind switching on the AC with defrost, but at about 34*F and below, R-134a pressure is so low, the thermistor keeps it off. It's that range from about 35 to 65*F is where it automatically switches on in defrost. 

Yet another problem that is age old and never solved is debris buildup on the condenser, restricts air flow and high side pressures can of up to around 400 psi! Get very little cooling and really putting one heck of a load on that compressor, water pump is the weak link and the first thing to go in a single drive belt system. Really made life difficult to keep that condenser clean. If you think your windshield is loaded with bugs, look at your condenser.

Another is stone chips, quickly learned on my that little plastic stone shield was missing, dealer didn't believe this, several looked at it, ordered one for me, installed it myself. Front license plate required in my state was actually a blessing, has stone chips in it.

Wasn't much of a problem with tube and fin condensers, one solid piece of copper tubing ran back and forth with R-12, R-134a requires a parallel flow condenser made out of super thin aluminum and is throwaway. R-134a PAG oil is hygroscopic and with moisture forms sludge that can plug up the orifice. Should be completely flushed, deep vacuum drawn, and PAG oil injected in to do the job right. Mineral oil never had this problem.

Yet another problem is that the EPA changed the service ports to a quick coupler from the old reliable Scharder valve, so you could not pour R-12 into these systems, have a tool that let me replace a 50 cent valve without discharging the system, now you have to replace the entire line with a leaking port. Uses a large disc that never seats properly that causes leaks, and while R-12 had a metal cap for the service ports, R-134a switched to plastic. 

CFC's were blamed for ozone depletion, but yet 95% of the total CFC production was never used for its intended purpose, all open spraying for spray cans and cleaning, less than 5% was used for refrigeration! And unlike leaded gas that was really a health hazard with a 20 year phase out, CFC's were banned overnight. And the manufacturers of CFC's were not held responsible, but up to the consumer to pay for the conversions.

DuPont came along with R-134a, now being blamed for global warming and while the EPA banned trichloroethylene back in around 1974 as being extremely dangerous, gave DuPont permission to use it for the production of R-134a.

Just a few bit of hard core facts why we are having problems and very expensive ones at that.


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## sailurman (Sep 29, 2016)

Mold, in PHOENIX??? BWA HA HA HA H HA


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