... try pouring some hot water in the tray. Might melt the blockage.
Thank you, people. Likely the ice. Can't defrost it now, fridge is full. Will have to clean the tray daily so that it wouldn't overfill.
Doug, will all due respect to your knowledge in this area, ice on the fins and in the tray is related to freezer temps, albeit indirectly. Thermostat is in the fridge as I understand. It cycles when fridge temp rises to whatever the thermostat is set to. In warm weather with sun shining on the fridge side of trailer, I have to set thermostat to Max to keep freezer below 4. This causes fridge to cool below 32 and freeze water in the tray, and sometimes to grow an impressive ice fur on the fins before it starts dripping to the tray.