Good news! Outside ambient temp is 64F at 6am today. A cold front came through last night - thank goodness! Temp in the fridge is 34F. I disconnected the temp sensor plug on the circuit board yesterday - that may or may not have had an effect. It's been on AC power for the past 16 hours.
Bottom line: I'm gonna visit a service technician and have the unit checked out and cleaned. Possibly replace some parts too. I hate to admit it, but I've done zero maintenance on the unit for almost 9 years - my bad. But I'm starting to think I don't really need a brand-new unit (yet).
