18,000BTU dometic split system. I noted the air wasn't as cool as it has been so I sought out a cause. Nothing obvious at the condenser so moved onto the air handle where I found the first 4" or so of the lines going in frosted. I checked the filter, washed it despite looking pretty clean, removed the ducts which were clean and flowing freely, turned the unit to high fan and within 10 minutes it was thawed. Both drain pans are dry but I still blew out the lines and ran water through them to ensure patency. Turned the unit back on and raised the temp from 70 to 74, IFR temp gun shows 83 at the filter, 71 at the vent. Any ideas where to go next, I'm thinking the only other option could be a leak. Will update in a few hours what the handler status is