While replacing the filter in our horizontal mount attic HVAC unit, I noticed the filter component (a large 4 inch wide filter) is located on the downside of the blower/coils. In other words, the air hits the filter AFTER passing over the coils and right before it goes into the ducts to the house. From what I have been able to find, the filter should be located at the point where the returned air enters the system, to filter out dust, etc. before the air passes through the mechanical parts. Hope this makes sense - I'm not so sure of the correct terms to use. I also read that the filter directional arrows should point in the direction of the air flow (obvious) but also toward the blower. This is impossible with our configuration since the filter is downwind of the blower. We're thinking the unit was installed incorrectly. Anyone know if this is an acceptable configuration or clearly an error?