View Full Version : A/C Filter

W.C. Turner
07-01-2005, 9:03 PM
I'm sure somebody here can answer this. The fiberglass filters, that are used in my central heating & air conditioner, have an arrow pointing the direction of air flow. I have always wondered, if it really makes any difference, which direction the filter is installed? Thanks. W.C.

John Miliunas
07-01-2005, 9:20 PM
W.C., I don't know that the direction of the material itself matter as to orientation, but you'll usually find some extra support material on the exit side of the filter (toward the air exchange) to keep it from collapsing and being sucked in.:) :cool:

Ken Fitzgerald
07-01-2005, 10:24 PM
On some filters there is a difference in the size of the filter material between the entrance side and the exit side.

Bill Turpin
07-01-2005, 11:00 PM
Good filters are gradient density. The looser material is encountered first by the air, this stops the bugs, ROCKS, and other large stuff. The smaller dust travels though and gets trapped by the denser media. If the filters were not gradient they would stop up sooner, because of the rocks. You should not buy filters that you can read a book thru. They don't stop much of anything.

NINETY % of all AC compressor failures are caused by stopped-up filters or stopped up evaporator coils caused by dust passing thru poor quality filters. Fifty cent to $1 filters from the BORGs or Walmart are worthless. Buy good filters from a HVAC supply. Good filters are more like $2.50. Cheap filters will cost you hundreds of dollars later. A SINGLE totally stopped up filter can cause liquid freon to return to crankcase of compressor. This causes discharge pressures of 3000#, instead of 300 lbs, discharge valves to chip, motor overheating, and motor failure(due to insulation failure...motor varnish melts) six months later called "burnout". Minimum repair is $600. Most lightning failures of AC compressors are really caused by dirty filters. When homeowners are asked what else failed...they say "nothing". If lightning caused the failure then every electrical device that was turned on would have blown up also, including all the light bulbs. Change filters when they are dirty, two weeks if necessary, not by some arbitrary schedule of the calendar. Lower light bill will counterbalance filter cost. The compressor will cycle off sooner.

RANT over!

Bill in WNC mountains
NC Refrigeration contractor license # 2821

W.C. Turner
07-02-2005, 1:54 AM
So, Bill,
I loosen 2 screws and the grating opens up in order to change the filter. Upon opening the grate, I'm facing the air filter. Am I correct, in assuming that the arrow on the filter, should be pointing in my direction?


Randy Moore
07-02-2005, 7:42 AM
No, the arrows should be pointing away from you. The air is sucked in through the return air registars and goes thru the filter BEFORE it gets to the motor/blower section, the air then goes thru the AC coil and on into the duct work and to the rooms. The filter protects the motor/blower and the coil so the don't get dirty and overwork themselves to keep you cool/warm.


Bill Turpin
07-02-2005, 6:21 PM
In a filter grille the arrow should point into the duct. If filter is in blower or furnace, it should point towards the blower assembly.

Bill in WNC mountains