On Monday, February 11, 2019 at 8:39:09 AM UTC-5, TimR wrote:
On Wednesday, February 6, 2019 at 3:16:22 PM UTC-5, Scott Lurndal wrote:
A dirty filter:

1) Reduces the airflow available to the heat exchanger. This could result
in the high-limit switch opening, which will increase the cycle time
(and blow colder air util the high-limit switch closes after the heat
exchanger cools sufficiently, rinse and repeat).

2) Causes the blower to work harder, which consumes additional power and
prematurely ages the blower.

A dirty filter does a couple of things.

It reduces air flow, perhaps very slightly to a lot.

It increases the efficiency of filtration. Dirty filters catch more dirt and work better, up to the point where reduced air flow becomes a problem.

If you reduce airflow enough, you might have coil freezeups or other problems. Residential systems tend to need a steady airflow across the coil, balanced to the temperature and the amount of charge. The old ones aren't intelligent enough to adjust, I dunno about more recent ones.

If your filter is dirty enough, theoretically it might rupture and spill unfiltered air into the equipment. The purpose of a filter is mainly to protect the equipment, not the humans. I haven't seen this happen in a residential system but I have in a commercial one. So I don't know if that's really a problem in a house.

I change my filter when I hear the sound in the return increase. That's probably about 3 months or so, I don't keep track. I just cleaned my refrigerator coils last night, they were caked with dust. (I have that stupid double A coil setup, where you can only reach the outer two rows.)



I wonder why the refrigerator companies haven't designed in a filter?
Same problem here, the coils are tucked underneath, you can't get to anything
more than the front of it to try to clean it. Not only would it be of
benefit to us, but it would be another revenue source for the companies,
selling the replacement filters. These suck in air at the worst place,
right at the floor surface where they pull in dust, pet hair, etc and
get dirty fast.