Bad smell coming out the vents when heater on or when I turn off AC

[Arese]

Hey guys,

So I got a really bad smell coming out of the vents when I increase the set temperature in the climate control system with AC on.

Also, when I turn off the AC, the same smell comes out regardless of the temperature set in the climate control.

My guess is that mold & germs built up in the AC system and when hot air is blown it's smelling bad. Based on the above symptoms would you agree with my diagnosis?


I've been doing some research online and on youtube and I found people recommending to spray disinfectant that kills germs through the footwell vents while recirculating air. Would that be effective? Any risk for the AC system?

Also found a video on youtube where the guys recommended spraying the disinfectant from the outside air intake located in the engine. Apparently, in Audi the air intake for the AC system is located behind the front grill.

Any thoughts?

Thanks

EDIT: Also read online that it could be a clogged drain hose.
Drain hose collects and removes condensation from your AC system. If that tube gets clogged, it can produce a swamp-like smell (or the water can spill out in undesirable places).
Anyone knows where this drain hose is so I can inspect it?

My car is an S5 S8.5 3.0T

[Audibot]

Have you changed your cabin air filter? Get one with an activated charcoal filter.

I have also done the spray through the vent when changing the filter for the peace of mind. Microorganisms like to collect on the evaporator. Also for the last few minutes of a drive, you could shut off the a/c, which may help prevent anything from growing.

[2by2handsofblue]

When you do spray disinfectant, remove the cabin filter. Use ozium

we are the borg! resistance is futile.

[Markie93]

Good morning,

I have the same vehicle as you and do not have any odors in my vehicle.

There are a couple things I would recommend. If you open up and look into the hood near where the engine bay meets your windshield there is a large plastic cover spanning over the entire width of the car. This is called the plenum cover and is near the hinges of your hood. If you remove this you will see where your air conditioning system sucks in air from outside. This often gets clogged with leaves and debris and then water that drains in there can't escape which can create mold and other issues. I would recommend taking this off cleaning inside the plenum and making sure the drains are free.

As another member mentioned, you should also look into changing your cabin air filter. I'm not sure if there is one or two filters but know that it's something very easy to change and is underneath your dash on the passenger side.

I used to have an old Lincoln that had really smelly air and it was because of a poorly designed AC system that wouldn't allow the condenser to properly drain. I've never had this issue with Audi vehicles I've had in the past or the one I currently have. My guess is you just have some debris someplace where it shouldn't.

Sent from my SM-N960U using Audizine Forum mobile app

[Arese]

@Audibot I do have 2 extra charcoal cabin filters and I was waiting to do my oil change to then replace cabin/air filter but I'll replace my cabin filter today if that's might be causing the bad smell.

@2by2handsofblue I never thought of that but it so makes sense to remove the cabin filter when spraying disinfectant into the vents. Otherwise I'd imagine that the pray would be caught in the cabin filter and wouldn't circulate/clean the whole AC system. Great tips thanks.

I will remove the old cabin filter, spray some disinfectant and then install the new cabin filter.


@Markie93 thanks for your reply.
Great, I wasn't sure from where the AC sucked in air from outside on this car. Thanks for the instruction, I'm going to work on it later today and clean the area.

Thanks guys, really appreciate I will keep you posted.

Also I came across this how-to online which seemed to be a proper way to clean car's HVAC
https://www.ebay.com/motors/blog/how...-conditioning/

To save you a click, here are the steps suggested by the tutorial

1: Clear the Drain Hose (I think I will keep this step as a last resort step as the car has only 30k and I think it's unlikely that the HAVC drain hose is clogged
2: Sanitize the System
3: Disinfect Every Six Months to Prevent Nasty Car AC Smells
4: Replace Your Cabin Air Filters

Basically, I will be doing steps 3-4 today by spraying disinfectant and replacing the cabin filter.

However, I've been curious about step 2 "sanitize" using an aerosol foaming cleaner to spray into the car's vents.
Has anyone ever used of those foaming aerosols? I'd love to hear more about this "sanitize" step which according to the article is different than the "disinfecting" step.



Thanks everyone as usual for the insightful answers

[2by2handsofblue]

Once its cleaned. Use it for about a week and get back to us. Let us know if it works.
Someone mentioned, when your ready to turn off the ac, turn on the regular air from the outside and higher fan speed for a few minutes. That might help dry the system. So that way u dont have excess moisture sitting in the system.

we are the borg! resistance is futile.

[Arese]

So I think I did a thorough clean of the HVAC system using Lysol disinfectant.

I removed the old cabin filter

- Sprayed from the footwell intake with recycled air turned on (AC on/off and heat and cold)

- Installed the new cabin filter. I used these new Mahn frecious filters with an extra layer on top of the charcoal layer.



The smell became less strong but was still present. I suspect that spraying disinfectant with the recycled air on didn't fully clean the system and the new cabin filter was probably the reason it smelled less. So at this point the issue wasn't fixed.

- I decided to look for the AC air intake where fresh air is sucked and I found it underneath the plenum cover



Removed the new cabin filter to make sure that disinfectant could travel through the whole AC system. (from air intake to being blown through the interior air vents)

With the engine on, AC off, and temperature set to HI and LO I sprayed the disinfectant which was being blown inside the car meaning that the spray did circulate through the whole system. It seems to have worked, no more smell so far.


Also last question, I noticed that when the AC is on, the air intake outside closes.

The below picture is the exact same location as shown in the above picture but as you can see you can no longer see the rotating fan and it's no longer sucking in air from outside.
Does someone know why? This air intake open when I turn off the AC and closes when I turn off the AC.

[2by2handsofblue]

So I think I did a thorough clean of the HVAC system using Lysol disinfectant.

I removed the old cabin filter

- Sprayed from the footwell intake with recycled air turned on (AC on/off and heat and cold)

- Installed the new cabin filter. I used these new Mahn frecious filters with an extra layer on top of the charcoal layer.



The smell became less strong but was still present. I suspect that spraying disinfectant with the recycled air on didn't fully clean the system and the new cabin filter was probably the reason it smelled less. So at this point the issue wasn't fixed.

- I decided to look for the AC air intake where fresh air is sucked and I found it underneath the plenum cover



Removed the new cabin filter to make sure that disinfectant could travel through the whole AC system. (from air intake to being blown through the interior air vents)

With the engine on, AC off, and temperature set to HI and LO I sprayed the disinfectant which was being blown inside the car meaning that the spray did circulate through the whole system. It seems to have worked, no more smell so far.


Also last question, I noticed that when the AC is on, the air intake outside closes.

The below picture is the exact same location as shown in the above picture but as you can see you can no longer see the rotating fan and it's no longer sucking in air from outside.
Does someone know why? This air intake open when I turn off the AC and closes when I turn off the AC.

I thought it would only do that when the recirculating air is turned on? The fan that is sucking air from the outside?
Strange.

we are the borg! resistance is futile.

[2by2handsofblue]

When you have the fan blowing, do you turn the speed up to max?
Does it make a difference if you turn up the temp heat and or lowering the temp?

we are the borg! resistance is futile.

[Arese]

I think you're right.

I usually have recirculating air turned on with AC on and I think the car remembers my last setting.

So when I was switching on the AC, maybe it was also switching on recirculating air which would explain why the AC air intake would close off, that would make sense.

Ok, I will double-check next weekend then because I'm keen to spray disinfectant into the AC compressor as well as I couldn't last time (AC intake closed)

But so far I the smell is gone, I think the smell was localised in the heater core/system as the smell was appearing only when I was turning off the AC. Now with the AC off the smell is gone so really happy about it :)

Thanks for everyone's help