Musty smell after using the AC on a hot day? Some tips to prevent such from happening

Do you often get a musty mildew smell from the HVAC vents on a hot humid day after using the AC? I know I do, especially since the CX-5's HVAC is quite prone to condensation. Here's a few explanations as to why it happens and some good habits for preventative maintenance.

(skip if you want the tips alone)
The smell is cause by condensation in the vents, which overtime with the addition of heat and lack of ventilation, may cause mildew and mold (fungus) to grow. Now, lets cut to the basics. What is condensation? Condensation is the conversion of water in gaseous form to its liquid form. It occurs when humidity is 100%- its saturation level. When a cold object, in our case a duct, meets a warm environment. Air sub-particles condense and form condensation, liquid phase of water.

The reason why the CX-5 is more prone to this is due to its automatic climate control (for those who apply). In full AUTO with the AC activated, it will keep a constant default of re-circulation mode. Thus preventing the evaporator coils from staying dry, when not in use, adding more moisture to the system. So good habits to help heavy moisture from forming in your ducts:



- After using the AC for extended periods of time, turn off the AC and make sure the blower is working without recirculation mode on. Leave windows cracked. Thus equalizing atmosphere pressure and humidity.

- Check if your car is forming droplets of water towards the front of the car near the firewall after extended standing and AC use. If not, then you may have a clogged evaporator drain. Mostly due to dirt forming from under windshield cowl.

- I have yet to find the exact location of the CX-5's evaporator drain, but I am almost 100% sure that it is the common firewall location. Should have a small rubber nipple located on the firewall.

Interesting... We HEAVILY use our AC in auto, and NEVER had any odor.

Have you tried using the AC in auto mode and then turning the AC off?

Try using this treatment product on the AC. Heard it get rid of moldy/musty smells.
https://www.amazon.com/dp/ (commissions earned)

I plan on trying the product on my 2010 Insight since I do get some musty/moldy smell after using the AC from time to time in hot weather.

Rather than using re-circulation mode I use use outside air mode to avoid the musty smell syndrome all together in the CX-5.

On my German made VW, it's a good idea to not only avoid the re-circulation mode but to run the heater full blast every now and then to help evaporate trapped moisture in the system.

The consensus (from reading various forums of AC topics) is that Japanese cars tend to have better AC condensation drainage designs than European cars.

^ This.

It would be nice if car manufactures would update their systems to automatically open the system to outside air when you shut the car off.

I'm generally pretty good about switching it over from recirc to fresh just before I shut the car off but on the times I forget to do that I can really tell as when I turn the car back on I get a blast of damp air.

For me, just switching it over to fresh as I park or as I pull into the parking lot if I think of it does the trick.

"For me, just switching it over to fresh as I park or as I pull into the parking lot if I think of it does the trick."

You're right, it definitely helps with drying the evap coils and somewhat for the ducts. That works for me for the most part as well.

I just also had musty smell when you turn the AC on for the first time. Have anyone had any musty smell issues so far?
I was looking into this on the web and mazda used to have service procedure spray coil coating in the condenser if I am not mistaken but no dealers in Pacific Northwest do this service. My local dealer has AC service that inject some chemicals but I do not think this would work as it does not get to clean the condenser coils. Any comments will be appreciated as I am little sad that less than one year old CX5 already have musty smell. (I did not over use AC and fresh air before shutting engine been adhered) Thanks

SayNoToPistons said:

Have you tried using the AC in auto mode and then turning the AC off?

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Yes... Going back and forth between AC on, and AC off windows down.

<shrug>

CX5BC said:

I just also had musty smell when you turn the AC on for the first time. Have anyone had any musty smell issues so far?
I was looking into this on the web and mazda used to have service procedure spray coil coating in the condenser if I am not mistaken but no dealers in Pacific Northwest do this service. My local dealer has AC service that inject some chemicals but I do not think this would work as it does not get to clean the condenser coils. Any comments will be appreciated as I am little sad that less than one year old CX5 already have musty smell. (I did not over use AC and fresh air before shutting engine been adhered) Thanks

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Makes me wonder where the condenser coils are actually located at? You want to ensure those coils are free of mold buildup and blockage of drip tubes. Chemicals sprays supposedly kill bacteria and helps clean things up to prevent blockage. I'd look for a natural less hazardous product and do it my self if possible since your going to breath the stuff in. Not sure if one exists.

I have always turned the air conditioner off about a minute before my destination. This saves gas and I've never had any musty smells.

I only use the recirculation mode for going through industrial pollution or if I see a vehicle in front of me producing clouds of burnt oil.

No problem observed with my GT, but I use outside air mode 98% of time.

Has anyone tried Lysol spray or others that have worked? if so, please let me know what has worked for how long.
Thank you

CX5BC said:

Has anyone tried Lysol spray or others that have worked? if so, please let me know what has worked for how long.
Thank you

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This is what you're looking for - 1Z Klima-Cleaner. It should get rid of the smell permanently.

I used 1Z Klima-Cleaner in my Infiniti QX. It definitely works for those who already have the on coming issue and is persistent even with the good habits mentioned.

Unfortunately it will come back with bad habits mentioned in OP.

This has worked for me on every car I own (10 years on some vehicles) in the hot and humid south. The problem is the cold air will add condensation to all the duct work after it's turned off. If you look at the chrome accent on the vents after a long run of A/C they will be misted with condensation. The condensation promotes mold/mildew growth.

After I reach my destination, I turn off the A/C, put the temp on 90 (heat) and blower on full for approximately 10 to 15 seconds. Windows down for comfort. This will dry out the ducts. It works! My wife does not like the process and routinely cuts her A/C off when she shuts down the car. I have to run Lysol through the vents in her car about once a year to kill the mold/mildew.