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Why Do Some Evap Coils Leak While Others Do Not? (Quick Tip)

Updated: Jul 13, 2023


Why do older coils seem to last a long time but ones that are only 10 or 15 years old leak? Energy transfer efficiency was not as much of a concern on older equipment and the tubing used in these older coils had a thicker outside wall dimension. On newer coils made over the last 20 years, the tubing in the coil is thinner, and in most cases, they have an increased surface area on the inside for quick heat transfer. The picture shows this increased surface area.

The problem is, the coils don’t seem to last as long when they have thinner outside walls especially on coils that have a galvanized tin plate on the sides of coil. This galvanized plate rusts and the reaction with the tubing creates leaks where the copper tube elbows are. We are now finding leaks on the tubing in the middle of the coil, leaks where the rusted tin meets the elbows, and leaks due to bad swaging and minimal braze joint coverage.


Be sure to check out our video on Where to Find R-22 & R-410A LEAKS on AC Units!

8 comments

8 Comments


John Corley
John Corley
Sep 21, 2023

That was one of the first things I was taught in plumbing, two dissimilar metals touching each other creates electrolysis. That's why they use brass and dielectric unions.

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Replying to

Not all dissimilar metals contact that create chemical reaction, however Aluminum with most metals cause chemical reaction, hence Aluminum ladders are not allowed in hazardous(classified zone 0 or 1) locations, elevated temperature environments as in coils catalyzes the reactions.

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John S.
John S.
Sep 20, 2023

Please do some videos on troubleshooting heat pumps. Specifically how to troubleshoot bad defrost board, and issues with defrost. Heating season is coming. Would be perfect.

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John S.
John S.
Sep 20, 2023

I purchased you complete set of Air Conditioning books w/ the E book included when I was in school. I was so far ahead of everyone else because I studied this book over and over.

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It would be interesting to know how much thicker the older coils were. X2, X4 ? Bet it is a lot. Would like to see a picture of an old coil cut apart. I did buy your book. Good book.

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John S.
John S.
Sep 20, 2023
Replying to

I would like to see a side by side comparison, as well.

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Mike Henry
Mike Henry
Oct 03, 2021

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Moreover, if you’re interested in some Wall-mounted DIYs, do check out our guide…

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