I hate to tell you this but I have this beat. Several years ago now a customer called for service, a new one that had moved to a house where we had originally installed the furnace and ac. I removed the coil, of course plugged up and asked the guy how often he had changed the filter? He replied that always once a month. He remarked how nice the new filter was, he just turned it upside down and just put it back in (he had replaced original with a washable). naturally I explained what happened. THIS IS A TRUE STORY!!
Oh, yeah! Now that's the kind of thing I get to see a lot. It's usually that exact same coil, too. I have seen worse, believe it or not, but I have no pics to prove it, so you have no reason to believe me . I've also seen plenty of plugged coils that weren't the HO's fault, though. In these cases, the HO really does change the filters every month, but never wonders why the filters are never dirty at all. Lots of filter bypass is the culprit and you often want to know how it was that did the install so you can kick them and laugh at them for such incompetence. Too bad your pick wasn't taken before the coil thawed . "I found the trouble, lady. You've got an iceberg in your duct."