Sunday 11 March 2012

Replaced Your Car's Cabin Air Filter Lately?

Many vehicles made after 1990 have a cabin air filter in the AC/heater (HVAC) system. Have you ever wondered why? It’s not just to clean the incoming air as the name suggests.

A couple of things happened to vehicles in those years that made cabin filters a great feature. First cars got smaller and evaporators – the unit that cools the air – got smaller. Second, the industry refrigerant changed from R-12 or Freon to R-134a because of ozone depleting substance regulations. 

Older, large evaporators had lots of space around the tubes and fins for moisture from the air to run through without freezing. Dust, pollen, bacteria that came into the car through the fresh air intake was washed out quickly by the freely running water. The smaller, more compact evaporators were redesigned to increase efficiency but they had little space for water flow. They also ran a bit warmer which didn’t pull as much moisture out of the air as before.

Since the muck didn’t wash off it sat on the evaporator and, when warmed up, smelled like a combination of rotten gym socks and a bad chicken sandwich. Customers complained and it was quite a procedure to clean the mess off and reduce the smell.

Along comes the cabin air filter which filters the dust and pollen before the air gets to the evaporator. Problem solved. 

But, now, without periodic filter service, air flow is restricted resulting in poor AC performance in the summer and poor heater in the winter.

They aren’t cheap, but they really work. Manufacturers specify replacement intervals which are the minimum. In dusty, warm, dry climates more frequent replacement is required. Don’t try washing them. They’ll disintegrate and become useless. Many service counters have a clean vs. dirty cabin air filter display. Trust them. They are real.

Bottom line: replace the cabin air filter before AC season starts in earnest. It’s good for business and good for customer satisfaction when the HVAC works as it should.


  1. Thanks for the reminder George.

  2. I find that changing them varies from a quick glove box removal to a stand on your head under the dash with fuse boxes and control units removed for access to a hatch that is attached with enough screws to hold back a tornado.But almost every time I inspect one they are disgustingly filthy.

  3. I agree with you. Makes you wonder if the engineers really thought things through first.

  4. milestherotarynut14 March 2012 at 09:29

    I get nasty hay fever and find the only time i get relief is when either i take a decongestant or am driving in my car due to the cabin filter filtering out the junk. And today with more and more people and there children that have asthma and other allergies it makes all the diffrence in the world to your quality of health .
    The placement of the acess for the filters can be a pain but if it was simple why would the customer come see the dealer, i aplaud the engineers for making stuff like that tough and creating job security for tecs.

  5. Interestingly, my 2007 Dodge Grand Caravan lists the cabin filter as an option which I don't have, but the air conditioner doesn't seem to suffer from the lack of it. My 2008 Nissan has a filter, and it has been filthy every time I've replaced it (glove box removal required) so I do think its very beneficial. It will be something I'll be looking for as a must have in future car purchases.

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