How to check a refer cooling unit for blockage

Running it too far out of level keeps the liquids from moving inside the tubes because there just isn't enough power from the convection process to force it like a compressor based fridge has.
If you have a blockage and manage to move it enough for the fridge to work, that blockage will still exist - just someplace else. The blockage wont ever just go away, it is rock hard.
At that point the cooling unit is extremely marginal in it's capacity and you can expect a short life from it.