[beenthere]

Did you cut a hole so that you are looking at the inlet or outlet side of the coil. Outlet side usually does look clean, when the inlet side is dirty.

 

[beenthere]

Usually, when I go to all the trouble to cut open a plenum to inspect a coil. I spray it with cleaner even if it looks clean. just to make sure.

 

[beenthere]

You should not have to clean a coil after 2 years or ever.

If a good air filter was always used, it shouldn't have to be cleaned after 2 years. No one knows what air filter was used by the original owner.

A 2.5 ton A/C on a 60,000 BTU furnace will have over 72,000,000 cubic foot of air move through it a year. It will eventually need cleaned.

The filter is supposed to keep the system clean.

Yes, the air filter is suppose to keep a standard furnace(not a condensing furnace or A/C coil)clean.

also the secondary heat exchanger will capture most of the dust, very little will go to the coil.

The secondary will get dirty, and will capture a fair amount of dirt, its maybe a MERV 4 to . A wet evap coil is about a MERV 8. So the evap will get dirtier then the furnace secondary.

it's not normal maintenance, it's a repair cause by another problem.

Evap coil cleaning is normal maintenance.

All you need to do is keep the filter and outdoor coil clean, open the blower compartment and check the wheel for dirt buildup.

And call a tech to clean the coil every so often. Unless you clean it yourself.

you can clock the gas meter to check the fuel input and check the temperature split in heating and cooling mode.

And still not know if all is well.

once's a system is properly set up you don't need someone year after year on such new equipment.

I have customers that never have their systems checked. I get to clean their evap coils every 3 to 5 years. They use MERV 8 filters.

Takes a well sealed MERV 11 or higher to keep the secondary and evap coil from ever needing cleaned(or for at least 10 years).

 

[beenthere]

You're assuming it's being changed and isn't leaking around the edges.

No, your assuming that it isn't leaking around the edges, and is changed regularly. I never assume that, since I know from experience that many do leak, and many are not changed as often as they should be. And that coils do need to be cleaned.

if it's doing it's job, shouldn't have to clean anything.

Wrong. A MERV 6 filter isn't suppose to stop all the duct and dirt. But its still doing its job.

what's the point of filter if it doesn't keep things perfectly clean? that's the whole point.

The average air filter isn't suppose to keep everything perfectly clean. Thats just a myth you believe.

Needs to be a MERV 11 or better to keep a furnace or A/C nearly as clean as you say a filter should keep a system. And there can be no leakage around the air filter, or its housing/cabinet.