With autumn rolling in the HVAC blower in my Subaru Outback seemed to be acting up. Whenever I’d have the blower at a low speed for basic air circulation it just… didn’t seem to be doing much. It turns out this was caused by the cabin air filter. The heavier filter, the Breathe Easy seen on the right, was restricting flow so much that I’d only get noticeable air movement when the fan was at ~2/3 of maximum or higher.
I’d swapped this filter in over the summer, and at first I didn’t notice, because I normally run the air conditioning (cooling) on a pretty high speed or have the windows down with the blower off. With temperatures dropping I’ll often have fresh air flowing in through the vents, but with the fan at a low speed, just to keep a fresh-air feeling inside the car. On the normal low (one or two bar) setting I just… wasn’t feeling much.
My thoughts first went to problems with an HVAC damper, or perhaps a motor speed controller, but then I remembered the activated charcoal cabin filter I’d fitted and wondered if maybe it was so restricting that the blower wasn’t working right.
Yep, that was the problem. I fitted up a simple Denso paper filter for capturing pollen and everything is working fine again. I’m glad it wasn’t anything more expensive.