Just a couple of quick questions:

1. When you have the air con set to recirculate, is that air passed through the pollen filter? (and do different cars vary on this, specifically thinking of the Fabia MkI here?)
   
2. At what point is the pollen filter generally located in the system (i.e. is it before or after the evaporator/condenser, heater matrix, fan etc)
   

Reason I'm asking is mainly is that my musty air con smell has returned when the system is first turned on or off and I'm trying to work out how to most effectively target it without taking the system apart! I was thinking of taking out the pollen filter and spraying some odour neutralising aerosol (or air con bomb/cleaner) down the outside air intake (with the air con and heater on, then hitting recirc once the can was empty), but I've read this can make the blower motor and flap motors wet and hence should be avoided.

The alternative is to spray the aerosol in the car with the recirc mode already on, but if recirc mode pushes air through the pollen filter I'd need to take that out first otherwise it's all going to end up in the pollen filter and not in the air con system (also not sure this avoids the motors getting wet, surely even in recirc mode the air has to pass them?)

Or I could even remove the pollen filter and spray the aerosol up the resultant hole (not sure if I'd want recirc on or off for this, would that get my aerosol closer to the evaporator than other methods? Anyway, help /advice appreciated as always.

Edited 24 August, 201213 yr by ckyliu

On recirc, all cars draw in some fresh air, which passes through the pollen filter. Many cars (such as the Mk1 Octavia which has the pollen filter in the engine bay) don't pass the recirculated air through the filter, as the inside of the car is not a source of pollen, seeds, leaves, etc. There are some cars that can take activated charcoal filters that do pass the reciculated air through a filter. You can often tell by the sound when you change to recirc. If the sound increases, a greater volume of air is coming out of the vents and is bypassing the restriction of a filter. In all cases, the filter is before the evaporator, heater matrix and fan.

Wet pollen on the filter or stagnent water in the a/c housing smells bad.

To exclude the filter, run the a/c without the filter.

A common cause of the mould smell, is water trapped in the a/c housing because the evaporator drain is blocked. There is no point treating the system, without first ensuring the evaporator drain is working.

You can by the charcoal filters for the Fabia too BTW.

I'm almost certain that on the Polo, Fabia and Ibiza the recirculated air still passes through the filter.

When I used to work as a car valeter (before it was called "detailing") we used to have a fogging machine for de-odourising a/c systems.

The advice was to first remove the pollon filter if it was inside the car then run the A/C on one fan speed down from full, blowing out of the dash vents, with recirculate on and the fogger on the back seat. Seemed to work very well and they always smelled like new afterwards.

Have you tried just running the A/C all the time for a while (even if you have the heater on)?

This may be enough to dry it all out and get rid of the smell. I notice that ours never smells (Climate control with A/C always on) but I was in a friends car who rarely uses A/C and theirs stank (was a VAG car with manual air conditioning).

Phil

On any VAG system I've looked at, the pollen filter is in the ambient air intake to the system, and recirc mode closes the ambient intake.

On any VAG system I've looked at, the pollen filter is in the ambient air intake to the system, and recirc mode closes the ambient intake.

Fair dos.

Just had it in my head it went through but I haven't really looked at the system in detail so I think we'll go with your answer

Thanks for the help everyone! Based on what I understand from your replies, I think the best technique would be to remove the pollen filter and set blowers 1 or 2 with air con and heater on, then spray the deodourising aerosol in to the resultant hole. Once the can is empty, plug the hole and set it to recirc for 10 mins with fans 3 or 4, before popping the pollen filter back in and airing the car out a bit.

Because Comma's air con cleaner from Halfrauds was over a tenner I was going to use something like Oust or Neutradol, but it turns out the dedicated air con cleaners are only about £3-4 a can from Eurocarparts and smell less, erm, "clinical".

Does anyone know where I can find the evaporator drain or how I can check it's not blocked? (PS: Please don't tell me this means taking the undertray off, because mine seems pretty stubborn at the moment. I don't think my Torx screwdrivers quite fit!)

I might try the Activated Carbon filter next time I swap it (the current pollen filter is not even a year old so I'm fairly sure it's not the source of the odours). Just for reference for any future readers, here are the part numbers for the cabin air filters to fit the Fabia MkI and a few other VAG models:

Standard 6Q0820367 (found online for £13.50)

Carbon 6Q0819653 (found online for £18)

Also found these carbon filters to fit the Fabia on eBay, seem legit.

Edited 24 August, 201213 yr by ckyliu

The evaporator drain valve is located at the rear of the engine bay where the two hoses pass through the firewall. The valve is behind a flap of heat resistant material.