a/c condensation line not draining
Given that it worked fine for a year, I wonder if something came loose and produced a dip in the line. I used to have to maintain a few dehumidifiers that were (supposedly) drained by garden hoses connected to the tanks. The garden hoses went down to a drain 12 feet below, so you'd think there would be plenty of incentive for the water to drain, and yet fairly slight bends in the hoses (not pinching them) that were below the tank would still manage to hang up the drains to the point that they would fill the tank and shut off. We'd go rearrange them and the tank would drain, but some time later things would shift enough that the problem recurred. It was not a good system.

Not sure if I'd go for trying to solve what's there, or putting in a larger drain line on general principles, but then, I don't know what size yours actually is, just that it seems common for A/C installers to use tiny pipes (and sometimes hoses, or sections of hose) for the condensate drains.