Unusal air vent smell under unusual conditions

[Tivan]

I thought of some time should I open this topic or not. At first, it may seem trivial or stupid... but, I do want to solve it and I think it's kinda interesting and may help someone else in the future.

 

So it's about smell from the ventilation. But not just any smell, and not just in any conditions. This is rather specific. At winter time (now) when heating is working and it's actually blowing heated air, IF I put my vents on recirculation (lets say in heavy traffic), the air coming out of vents smells... well.. its more like air coming out of a bag vacuum cleaner when the bag is full. It's a dusty smell and also kinda as if there is a hint of wood ash (like if you vacuumed the stove a bit and then what vacuum cleaner smells afterward).

 

Mind you, I cleaned all the ducts in spring last year. And i did drop as much as I could AC cleaning foam onto evaporator from the middle console duct hole. I cleaned the ducts with damp microfiber cloth (from inside) and also some chemicals for disinfection of home AC and then some AC deodorant afterwards. I regularly change cabin filter (twice a year) and I use the AC spray at least once a year. In summer, I try to dry off the AC after coming to a longer stop. My car is not that humid, windows do not fog up unusually and then do clear quickly in winter. No smells in summer.

 

This problem ONLY happens when recirculation is ON and when the engine is warm enough to actually heat the car. Also as soon as I turn of recirc. no smell.  If I turn on recirculation when It's still blowing cold (after starting the car with cold engine), no stink. 

[varaderoguy]

Okay - two areas of checking:

 

1) Make sure your cabin air filter is clean.  Try running some AC cleaner through the car - something like: https://www.autoglym.com/air-con-sanitiser

2) You could have a condenser leak and what you are smelling is R1234 refrigerant.  If Point 1 is not the problem, get down to a garage with the relevant HVAC/AC recharging kit, get them to test the pressures (hi and low side).  If its low, then get them to put in a HVAC coloured dye and repressurise.  Check the Schraider valves.  If the smell is still there, then it requires checking out the heater matrix in the car and finding the leak.  You can get leaker detectors to try and find the refrigerant. Could be coming from the heater matrix in the car.

[Tivan]

Its def not 1).

 

Not sure what you mean by "condenser leak". Nothing is wet in the car and as far as I could tell in the summer by observing puddles under the car, condensate is draining correctly.

My car has older style of refrigerant, but regardless, I kind of doubt It's that as well. First of, I had same smell 2 winters ago after which I did detailed spring cleaning of AC system (mentioned in original post) and that helped for one winter season. I have not done anything to my AC in regards to service of it since car was 3.5 years old (since i own it), so if it was leaking that much so it can be smelled, by now I would probably have zero gas inside of it and no cooling effect at all in the summer.

Second, smell of the refrigerant should be more like electronics smell? If so, that is nothing like what I have.

 

My theory so far is that somewhere in the ventilation system there is still dirt and fine dust buildup. So when car is recirculating hot air, that creates humid enough air that it triggers that dust on the vents and produces the smell. Then again, why does it not happen if there is no recirculation, but there is a ton of fog outside...that surely is humid air coming into the car from the outside....

[Gammyleg]

Do you always run with the A/C switched on? If you switch it off for periods of time condensation/water can build up in the ducting and creates a horrible smell in the car when switched back on again.

 

 

[Tivan]

I almost never turn of ac, summer or winter. 

[varaderoguy]

You don't have a dead animal (such as a mouse) that has died and is decaying somewhere in the air duct?

[J.R.]

B.O. ? 😁

 

You did say it was only during recirculation mode!

[J.R.]

A dead animal that has died? Not much luck even in the afterlife!

[Tivan]

😁

I imagine I would discover the problem in a different way if it was dead body in there...