Hi there,

I have a 2013 Ford Focus and for a number of months now I've been getting an acidic smell from the air conditioning, particularly when the "air circulation" setting is engaged.

I took the car to a garage shortly after finding the problem and they did a full vacuum of the system and applied deodoriser which worked for a short time and then the smell came back again.

Recently I noticed the air conditioning was blowing warmer than usual, so took the car to another garage I've used many times before for a re-gas. A full clean of the system was done and the gas topped up.

After a couple of weeks the smell came back again. The car doesn't get a lot of mileage per week and I've noticed the smell is stronger when the car is sat in the sun, and can happen if it's been sat for days or sometimes only hours.

If I drive for a couple of miles and run the air conditioning full blast for a short time it will often clear through but I've only noticed this problem in the last 6 months or so.

The car is serviced yearly which includes changing of filters so I'm at a loss on what to do next.

Any ideas?

It's very difficult to fully clean the HVAC system unfortunately.  The only thing you can do is keep putting deodorisers or anti-bac foams through the vents, but they only have to miss a small section of the evaporator, leaving a bit of bacteria or mildew behind, and that will start to grow again as soon as the AC is next used.  This is particularly bad on cars that only do short journeys as there isn't enough time for the evaporator to start drying off, it gets very damp initially as it pulls the moisture out of the car, then when you stop it remains damp with no airflow, which is ideal for things to grow.

Regassing won't make a difference to this, and generally it isn't caused by the pollen filter either.  You can try checking that the water is draining out under the car when AC is in use.  If it's not draining properly then it'll be holding even more moisture in the HVAC box.

I've had the same issue on a few different cars.  Even using professional cleaning products.  But it seems that once it's started, it never goes permanently again.

its rotting skin cells and other dust and debris

play your cards right and you can get legionella too - the best cure is to leave the AC on all the time and most bugs freeze to death - plus you can see where you are going in the winter....

Freezing doesn't kill bugs.  And the compressor gets switched off before the evaporator can freeze anyway.

The better option would be a short burst of super hot air at 60c+ once a month, but I've never seen that option available on any car.  I'm not even sure if the vent ducts could handle it.

Am I likely to be stuck with this issue then? I'd rather not have to take it to the garage again if there's something I can do myself...

27 minutes ago, Shoxt3r said:

Am I likely to be stuck with this issue then? I'd rather not have to take it to the garage again if there's something I can do myself...

The garage can't do anything special so there's not much point taking it back there. 

You can buy the same disinfectant they'd use and do it yourself.  This is one example.

https://simssuzukiparts.co.uk/products/new-genuine-wurth-air-con-conditioning-disinfectant-300ml-hose-spray-089376410?

But the difficulty is getting it to completely cover the whole evaporator and the walls of the HVAC box & ducting.

5 hours ago, TomsFocus said:

Freezing doesn't kill bugs.  And the compressor gets switched off before the evaporator can freeze anyway.

 

ask your wife if she keeps food in a fridge frezzer

14 hours ago, Botus said:

ask your wife if she keeps food in a fridge frezzer

Fridges and freezers don't kill bacteria, they just slow down the rate of reproduction. Freezers almost stop reproduction but they still don't kill the bacteria.

Before taking it to the garage I did try using this within the passenger footwell which made a bit of a difference before the smell came back again.

https://www.halfords.com/motoring/car-accessories/all-car-accessories/autoglym-air-con-sanitiser-450350.html

I've looked on YouTube and found this video which suggests to apply disinfectant to the vents under the windscreen. One comment even suggests to remove the air filter and use a foaming product as well?

 

Any thoughts on these options? Is it basically that once it starts, I won't ever be able to fully clear it?

2 hours ago, mjt said:

Fridges and freezers don't kill bacteria, they just slow down the rate of reproduction. Freezers almost stop reproduction but they still don't kill the bacteria.

I'm just imagining Botus licking a frozen chicken drumstick like an ice pop now...

2 hours ago, Shoxt3r said:

Before taking it to the garage I did try using this within the passenger footwell which made a bit of a difference before the smell came back again.

https://www.halfords.com/motoring/car-accessories/all-car-accessories/autoglym-air-con-sanitiser-450350.html

I've looked on YouTube and found this video which suggests to apply disinfectant to the vents under the windscreen. One comment even suggests to remove the air filter and use a foaming product as well

 

Any thoughts on these options? Is it basically that once it starts, I won't ever be able to fully clear it?

The spray cans don't work for long because they don't fully coat the area inside the HVAC box and it's mostly getting blown out again anyway.

I would recommend either a long flexible tube spray as in the earlier link, or a foam spray, as both of those will give better internal coverage and can be left to dwell for a while without the fan running.  But there's still no way of knowing whether you've covered everything or not, until a week or two later when the smell returns.

9 hours ago, TomsFocus said:

The spray cans don't work for long because they don't fully coat the area inside the HVAC box and it's mostly getting blown out again anyway.

I would recommend either a long flexible tube spray as in the earlier link, or a foam spray, as both of those will give better internal coverage and can be left to dwell for a while without the fan running.  But there's still no way of knowing whether you've covered everything or not, until a week or two later when the smell returns.

Ah ok thanks for the help!

Interestingly, I went out for quite a drive in the car earlier and left the recirculating setting off and just kept the A/C running and barely noticed a smell coming through.... Any ideas why that would be? I usually use the recirculating option to get the cold air to flow faster but that's what appears to be causing the smell to come through.

I rarely use the A/C option and often turn it off if it automatically comes on - is that part of the problem?

recirculating air will cause the problems as it stops fresh air comeing into car, so all your doing is blowing stale air around and around the car, i never have my air-con off, cars loose about 10% of gas a year

 

11 hours ago, Shoxt3r said:

Ah ok thanks for the help!

Interestingly, I went out for quite a drive in the car earlier and left the recirculating setting off and just kept the A/C running and barely noticed a smell coming through.... Any ideas why that would be? I usually use the recirculating option to get the cold air to flow faster but that's what appears to be causing the smell to come through.

I rarely use the A/C option and often turn it off if it automatically comes on - is that part of the problem?

Recirc sucks air from the footwells so if you've got any damp or mould down there (or smelly feet!) then it'll be blowing that straight at your face.  Fresh air is best, unless you're stuck behind a bin lorry or trying to dry the screen in very humid weather.

 

In my experience, using AC regularly doesn't prevent it smelling, leaking or breaking.  I rarely use AC myself as I hate the drying effect it has on my face.  But I also hate heat so have to use it for cold during the summer.  I've never had an AC system leak or break during my ownership from that type of use.  Conversely, my Mum owned her car from new, never turned the AC off, and by 10 years old it started breaking about once a year until she eventually changed car.  Both of us had issues with smelly AC.  In theory you should get fewer problems with if you leave it on permanently from new but there are a lot of other factors as well.  As mentioned earlier, if you do a lot of short journeys, leaving the AC on for those seems to create more problems, leaving it warm and moist when you park, which is another reason I rarely used mine.  It's worth noting my experience of AC seems to be different to most other members on here, so make of that what you will.  

I always switch my AC off several minutes before finishing my journeys but leave the rest of the Heating System on to dry the Ducts and I have never had a problem with smells in any car I have owned. It is probably too late to do that if the smell is already there.

Using Recirculation for any length of time is not good for your health, if you want to cool the car quickly then leaving a window open until the system is cold enough is preferable. 

1 hour ago, Tizer said:

I always switch my AC off several minutes before finishing my journeys but leave the rest of the Heating System on to dry the Ducts and I have never had a problem with smells in any car I have owned. It is probably too late to do that if the smell is already there.

Using Recirculation for any length of time is not good for your health, if you want to cool the car quickly then leaving a window open until the system is cold enough is preferable. 

Ok that's good to know, will bear that in mind for future.

Well, today is the second day of driving the car out with AC active only and there has been no smell coming through the vents so hopefully that will be the last of it.

I will have a check and see what's happening in the footwell though just to be sure there is no dampness.