3rd Evaporator Coil American Standard a/c

It is the crappy aluminum coils they are using now vs the old ones that were copper. It is not just American Standard, I have replaced two Lennox aluminum coils on two separate units I have. I got two years out of both of them. They were replaced under warranty, but that did not include the labor, evacuating, and refilling the system.

The aluminum coils also are not as antimicrobial as the old copper ones. They seem to develop the dirty sock smell syndrome a lot easier. I had them set the blower to run a little longer when the condenser cuts off, it has helped somewhat.

Evaporator coil leaks are problematic, regardless of manufacturer, particularly in newer systems, as coils are being made larger and with thinner metal (aluminum) to gain greater heat exchange efficiency to achieve higher SEER and EER rating being mandated by the Feds. Coils are more energy efficient but they are not as robust as in older units with thicker, heavier metal.

But unless you have incredibly bad luck, with 3 evap coils in 2 years it sounds as though you may have a contaminant in the system eating away at the coils. Often an acid created in the refrigerant loop by the refrigerant reacting with moisture - water moisture would be present if the installers failed to pull a proper vacuum on the system and didn’t install filter/dryers, and that applies to each subsequent evap coil replacement. But I find it difficult to believe that a reputable company would fail to do those things - as that’s a standard/required installation practice, and only a hack would not do those things. I wonder if I could even a mechanical abrasion issue. But clearly you need a a good HVAC diagnostician to find the root cause of this issue.

I’d recommend you register on the AOP Residential forum of HVAC-Talk, pose the same question, and let experienced HVAC technicians from around the USA provide their thoughts on what might be the cause of this and they’ll usually offer advice to steer you in the right direction. Here is the site LINK and if you do register and post give them as much information as possible on your system - model numbers of your outdoor condenser, air handler and coil. Is your air handler in a closet, in the attic, etc - the more info you provide the better they can help you.

Your attic wouldn’t happend to be spray foamed would it? I hear of houses with spray foam and multiple bad evaporator coils being thing.