Recurring A/C Odour in MG4 - Seeking Advice

Ori · Jan 14, 2025

Hello,

I own an MG4, and I’ve been experiencing a recurring issue with the air conditioning system. Recently, I noticed a strong odor when turning on the A/C (cooling mode only). After replacing the cabin air filter, the smell disappeared temporarily. However, after leaving the car parked for a few days, the odor returned. It only lasts for a few seconds to a minute when I initially turn on the A/C, then it dissipates.

Upon investigating, I observed two air intakes behind the cabin air filter—one for external air and another for recirculated air. After some tests, I found that when the A/C is turned off, the default state of the system is to close the external air vent, effectively sealing the system.

To address this, I manually changed the air intake mode to pull in external air (with the A/C off), which did open the external vent. However, as soon as I turned off the car, the external vent closed again, leaving the air conditioning system sealed.

I suspect that residual moisture on the evaporator or radiator isn’t drying properly due to the system being sealed when the car is off. This might be the cause of the recurring odor.

Could this issue be related to the software version? I currently have R59.

Has anyone else experienced a similar problem and consulted a service center? Is this behavior normal, or should it be addressed?

I’d greatly appreciate any insights or advice.

Thank you!

ReintjeWA · Jan 14, 2025

I’ve had this in one of my previous ICE cars, it’s probably mould in the system. That’s a though one to clear I believe.

Ori · Jan 14, 2025

ReintjeWA said:
I’ve had this in one of my previous ICE cars, it’s probably mould in the system. That’s a though one to clear I believe.

I thought to but If it’s mold, how is it possible that the odor only occurs in cooling mode, only during the first activation of the A/C, and disappears within a few seconds?

ReintjeWA · Jan 14, 2025

Wezzo said:
I've had my new MG4 Xpower a few months now. It was an odd experience at first but have settled in and am happy with it overall, but have a few suggestions for improvement.

- AIRCON: I am a microbiologist presently working with mould (mold) and often see vehicles with harmful amounts of mould growth on the dashboard, windscreen and vents because it grows very fast on the wet chiller fins and coils when the car is turned off before the fins dry off. They warm up and this makes everything humid in the A/C system and nearby, including the whole car cabin interior if the windows are kept closed and the weather is warm and humid. People get quite sick from this, and it is expensive to remove it all as just spraying with something does nothing good.
Hence, a safety feature would be to have the fan continue to run for at least 5 minutes after the car has stopped and the A/C was in use, longer if cool humid weather. Ideally there'd be a moisture or humidity sensor in the A/C heat exchanger that detects when the fins are wet / dry and activates the blower accordingly

This was posted not too long ago in the Wishlist thread, I’ve only quoted the relevant bit.

Wish list of MG4 improvements

Tried my 11,000+ tracks on one USB stick. I think all the tracks are there and could be accessed sequentially, but I haven’t the time or energy to click next track forever. The main display shows “No Tracks”, so no joy and back to my four sticks with fewer tracks each. Could you tell me what...

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ReintjeWA · Jan 14, 2025

Ori said:
I thought to but If it’s mold, how is it possible that the odor only occurs in cooling mode, only during the first activation of the A/C, and disappears within a few seconds?

Yeah I’m not too sure, but I remember in my 308 it would stink worst when cooling on recirculation mode, and really only for a little bit right at the start. The smell would then dissipate.

Running the A/C with outside air regularly did help, but I doubt it ever really cleared the system. I knew the car was going to be replaced relatively soon so never really got stuck into it.

Ori · Jan 14, 2025

ReintjeWA said:
Yeah I’m not too sure, but I remember in my 308 it would stink worst when cooling on recirculation mode, and really only for a little bit right at the start. The smell would then dissipate.

Running the A/C with outside air regularly did help, but I doubt it ever really cleared the system. I knew the car was going to be replaced relatively soon so never really got stuck into it.

It’s possible that there is indeed a buildup of bacteria or mold in the system, which could explain the odor. However, I don’t quite understand how the smell dissipates after just a few seconds, and why it only occurs in cooling mode and not in heating

.
I’ve also come across anti-bacterial sprays, but I doubt they would truly solve the issue. If my theory is correct, the problem would likely return, making it more of a temporary fix than a solution.
I hope more people respond, especially those who have found a permanent solution.
By the way, do you also have an MG4? Have you encountered this issue yourself?

ReintjeWA · Jan 14, 2025

Ori said:
By the way, do you also have an MG4? Have you encountered this issue yourself?

I have an Essence 64 (Australian version of the Throphy LR) and have not had this particular issue in my MG4, only in one of my previous cars.

Ori · Jan 14, 2025

ReintjeWA said:
I have an Essence 64 (Australian version of the Throphy LR) and have not had this particular issue in my MG4, only in one of my previous cars.

But maybe do you know if the air intakes behind the cabin air filter act the same?

ReintjeWA · Jan 14, 2025

Ori said:
But maybe do you know if the air intakes behind the cabin air filter act the same?

Never checked so couldn’t say for sure but I’d be surprised if they act different from what you’ve observed. Maybe ask this thread if they know?

Cabin Air Filter replacement

When I had my MG4 serviced. after the service, the car stank like a perfume factory. I found out that the replacement cabin air filter was sprayed with aftershave/perfume of some type. One thing I noticed is that there were two slots for air filters (one above the other), but I was only given...

www.mgevs.com

gazza487 · Jan 14, 2025

Check that the drains are clear not sure of exact layout but there will be tube from evap to floor.

Had it on a few older cars before. On the cold side as it’s when the bacteria is warm and releasing volatiles. As soon as the evap gets freezing cold less of the smell boils off and you’ve cleared any existing buildup of the smell out of it.

Never had much success with the bomb type cleaners other than getting in too soon as getting very wooozy. You can buy foam type cleaners that have a tube that’s meant to go down the vents - I shoved it up the evap drains (rightly or wrongly) so foam got directly to it on a 75 I had.

All manufacturers should add a few UV leds on a timer like some Lexuses did. Alas, they don’t.

Ian Key · Jan 15, 2025

You could try an AC sanitiser where you set off an aerosol in the car with the AC on and set to recirculate. They are available from Amazon.

Ori · Jan 15, 2025

Ian Key said:
You could try an AC sanitiser where you set off an aerosol in the car with the AC on and set to recirculate. They are available from Amazon.

I saw some aerosol but I want to make sure it will not come again

gazza487 said:
Check that the drains are clear not sure of exact layout but there will be tube from evap to floor.

Had it on a few older cars before. On the cold side as it’s when the bacteria is warm and releasing volatiles. As soon as the evap gets freezing cold less of the smell boils off and you’ve cleared any existing buildup of the smell out of it.

Never had much success with the bomb type cleaners other than getting in too soon as getting very wooozy. You can buy foam type cleaners that have a tube that’s meant to go down the vents - I shoved it up the evap drains (rightly or wrongly) so foam got directly to it on a 75 I had.

All manufacturers should add a few UV leds on a timer like some Lexuses did. Alas, they don’t.

Do you have any recommendation? The foam cleaner did solve your problem?

Kithmo · Jan 15, 2025

I looked into this many years ago when I bought a smelly, nearly new, ex company Mondeo.
The solution is to run a sanitiser through as @Ian Key says, then afterwards run the heater with AC and the heat set to HI, as often as comfortably possible, to dry the system out.
Also, try and obtain a charcoal infused cabin filter, if one is available, they filter out odours.

gazza487 · Jan 15, 2025

Ori said:
Do you have any recommendation? The foam cleaner did solve your problem?

It was some off brand thing on eBay many many years ago I’m afraid. Didn’t smell nice but was a cleaner

Ori · Jan 15, 2025

Kithmo said:
I looked into this many years ago when I bought a smelly, nearly new, ex company Mondeo.
The solution is to run a sanitiser through as @Ian Key says, then afterwards run the heater with AC and the heat set to HI, as often as comfortably possible, to dry the system out.
Also, try and obtain a charcoal infused cabin filter, if one is available, they filter out odours.

But how it comes at the first time? Maybe there is a leak in the gas system and if there is so sanitizer won’t help because it will grow again

gazza487 · Jan 15, 2025

Ori said:
But how it comes at the first time? Maybe there is a leak in the gas system and if there is so sanitizer won’t help because it will grow again

Bacteria in the air hits the evap which is cold and damp, when it’s turned off it’s warm and damp it grows.

Ori · Jan 15, 2025

gazza487 said:
Bacteria in the air hits the evap which is cold and damp, when it’s turned off it’s warm and damp it grows.

It’s not my first car but it’s the first time I have this smell so if I understand what you say it’s will be back every time

gazza487 · Jan 15, 2025

Ori said:
It’s not my first car but it’s the first time I have this smell so if I understand what you say it’s will be back every time

Potentially yes. You do not control what the car sucks in, if somebody sits inside and sneezes, parked under a tree and so on. It may go and never come back once cleaned or it may come back again.

Without something to disinfect it - anything can happen.

NickHeynes · Jan 15, 2025

I don't suffer with any smells but I did notice that when I first had the car you could feel a gentle breeze of air being drawn into the cabin when the a/c was off . Since having the latest SE update i can't feel it. Maybe the updates have changed something .

Kithmo · Jan 15, 2025

Keeping the vents dry will make it less likely to come back as will plenty of fresh air.

Recurring A/C Odour in MG4 - Seeking Advice

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