Owning a Volkswagen means dealing with a few quirks you won’t spot in the showroom, and might not even notice for a few years after you’ve bought your car.
One of these is a foul smell from your VW’s air conditioning system. Whether it’s a Golf, Polo, Passat or any other model, that smell usually points to something you can fix without too much hassle.
In this blog, we’ll walk you through the likely causes of your VW’s air con smelling bad, and look into what you should do about it.
Blocked AC drain tube: ‘damp’ smell
The air conditioning system (in any car or building) is quite clever. It doesn’t make cold air; technically, air conditioning removes the heat from hot air. It then releases this heat into the air.
A happy byproduct of this heat exchange system is the removal of moisture. The same process that removes the heat also causes the water in the air to condense. That means you get cold, dry air pumping into your VW’s cabin.
Now, that water has to go somewhere. There’s a drain tube to make sure it drains away harmlessly, down onto the road. (That’s why you sometimes notice a puddle under your car if you park it after running the AC.)
However, if that drain becomes blocked, even partially, water starts to pool inside your AC unit. You might be smelling something like a damp towel or wet concrete. The water can lead to corrosion and rust, but standing moisture also provides a breeding ground for mould and bacteria. We’ll touch on that in the next section.
So, if you don’t notice a puddle under your car when you’re parked after running the air conditioning, that could be a sign of a blocked drain tube. It could also be a few other things, some harmless. It’s a relatively simple job to clear it, but check with a trusted technician if you’re unsure.
Blocked AC drain tube: ‘foul’ smell
It’s what happens after water starts pooling that’s most concerning. That’s when microorganisms (bacteria and mould) move in and start spreading.
They’ll attach to the cold coils, vents and all the internal surfaces, almost always behind the dashboard, where you can’t see.
Over time, they’ll start releasing smelly gases. The specific smell can depend on the type of mould or bacteria that happens to be growing. Still, it’s often a sort of sickly, bitter/earthy/musty-type odour. That’s what you smell when you switch on your VW’s air con.
Over time, it might get worse, and if the microorganisms spread onto the vents themselves, you might smell that bad smell even when the AC system is off but the blower is still on.
If you have a bad mould problem, you should be more careful. Most mould is just an irritant, but some kinds can be hazardous to breathe in, especially for individuals with breathing difficulties, such as asthma. If you suspect you have a mould/bacteria problem, bring your car to us at Sunset VW in Derby. We’ll handle it for you.
Cabin air intake blockages: ‘foul’ smell
The ‘cabin filter’, also known as a ‘pollen filter’, in a modern car removes dirt, dust and debris particles from the air before it blows into the cabin.
Whether you have the air conditioning switched on in your VW or not, all the air coming through the blowers has passed through the cabin filter, unless you have recirculate mode on, of course.
Now, the cabin filter is designed to trap particles. If it doesn’t get changed regularly, it clogs up. That can mean it starts restricting airflow and trapping moisture. Eventually, those damp conditions could make an ideal breeding ground for mould.
Sometimes, we might find a crack or a leak in the cabin air intake vents or around the cabin filter itself. That might also be allowing water in, for example, when it rains or the roads are wet, and the same mould- and bacteria-breeding conditions arise.
Finally, in rare cases, you might find that your cabin air intake vents are full of small pieces of debris, like leaves or tiny bits of twigs. Over time, and especially when combined with a water pooling problem, these items begin to swell and rot. That would create an unpleasant smell coming from your vents.
Engine coolant leak: ‘sweet’ smell
Your engine burns fuel. That means it gets hot. To keep it from getting too hot, your car pumps water through little channels to absorb the heat. The water then passes through the radiator, where the heat is released into the outside air.
This is a great system, apart from the fact that the water would freeze in winter. So, we add something called antifreeze, which does what it says on the tin. Antifreeze is usually either ethylene glycol or propylene glycol. This water + antifreeze mixture is what people typically refer to as coolant.
Because of its chemical composition, antifreeze can have a sweet, sickly, almost fruity smell. So, if you smell something along those lines coming through your vents, it could be coolant, especially if there’s a leak from the heater core or a hose or gasket near the dashboard.
When the engine is cool, which is very important to avoid getting scalded, open and secure the bonnet. Check the coolant levels. If it seems low, top it up to the ‘MAX’ level. That way, you have a reference point for the next time you look.
While you’re there, look for any obvious signs of water spraying inside the engine bay. This is obviously much easier to do on a dry day.
If in any doubt, come to see us as quickly as possible. We’ll do a few quick tests to establish if you have a coolant leak, then explain what to do next.
Air conditioning refrigerant leak: light ‘chemical’ smell
Your VW’s air con system contains a refrigerant, which is basically a chemical that can consistently hold very low temperatures. It moves through the system using a compressor. As it flows, it passes through parts that change its pressure. This makes it switch between a liquid and a gas. That switch, combined with a couple of other components, is what removes heat from the air before it reaches your vents.
Inevitably, sometimes the pipes or components, such as the compressor, evaporator or condenser, develop leaks. These kinds of leaks are usually caused by microscopic cracks resulting from debris impact, certain fittings, brittle rubber seals and O-rings, etc.
An air conditioning specialist, such as us here at Sunset VW, will use a clever dye and ultraviolet light to pinpoint the specific cause of the leak and make the necessary repairs.
It goes without saying that the chemicals involved in air conditioning aren’t for breathing in, so get your VW inspected promptly. Also, you need special qualifications to handle air conditioning refrigerants, as they’re often very bad for the environment. This is one job that’s best left to the experts.
If you suspect a refrigerant leak in your VW’s air conditioning system, please give us a call. We’ll walk you through the next steps and schedule a quick check-up for you.
Habits to stop your VW’s air con from smelling
And finally, here are a few habits to help you look after your air conditioning system and stop that bad smell from returning:
- Run your air conditioning as often as possible, even in winter. The air con system also contains some oil, which prevents the rubber seals from becoming brittle. It goes a really long way in preventing leaks. You can still turn up the temperature when the air conditioning is on.
- Avoid overusing recirculate mode for long periods when the AC is off. Without the drying effect of the air conditioning, moisture stays in the air and creates a damp environment, allowing more room for bacteria to grow.
- Get all your car’s air vents and water-based systems serviced. All sorts of things can go wrong and create an environment where humidity builds up, leading to bad smells.
How we fix the bad smell from your VW’s air con
The good news is that these problems are all totally treatable, and often without huge cost. At its most basic level, these are all cases of finding what needs to be replaced, removed or cleaned, then doing just that.
When you bring your VW, Audi, Seat or Skoda in with a bad-smelling AC, we’ll listen to everything you have to say. Even if you don’t know much about cars, your knowledge of your specific model and experience driving it is invaluable.
Based on what you say, we’ll probably be able to narrow it down to two or three possible root problems. We’ll probably take at least one, probably more, of the following approaches:
- Inspect and, if needed, clear the evaporator drain path.
- Perform a sanitising or antibacterial treatment inside the system, targeting the evaporator and vents.
- Clean out the cabin air intake vents and replace the cabin filter.
- Test the coolant system for leaks.
- Test the air conditioning system for leaks.
If your VW’s air con has started smelling, you don’t need to live with it. Bring your car to us, and we’ll give it a full check and cleaning. You’ll leave breathing cleaner air, with no damp or mould smell wafting through your vents. Book an appointment today.