Since people seem to be online now, I'd appreciate some enlightenment on this matter please
I'm having trouble figuring out what you mean by "damaged" (which is the heart of the problem with AE), so without using metadata numbers or a screenshot I'm having issues figuring out what you're actually doing.
However, what you're probably experiencing is AE defines damage as 0% at fully repaired and 100% at fully broken. This is
opposite of metadata (and heat), which counts
up as you damage an item.
EDIT: If you want to test this for yourself, go into a creative world and get a 5/12 durability and a 2/12 durability wooden shovel. Filter on the 2/12 durability shovel and split damage at 75%. The 5/12 durability shovel doesn't match because it's not on the same side of 75%
damaged as the 2/12, even though the metadatas are on the same side of 75% of their max value.
EDIT 2: tl;dr - heat counts up while AE counts down. If I've read your post correctly, once the coolant cells hit 75% AE goes "Well, this one thing is 99% damaged and one is 25% damaged and he's splitting at 25%, that matches". Change to split at 75% for better results.