The Evap' coil fins are plugged with frost/ice due to an air leak letting in too much humid air, this flow of warm air forces the T-stat to keep the compressor running, then you get a film of frost over the fins & it ( bad pun warning) snowballs from there
so shut off the T-stat, let it defrost & track down where the air leak is coming from.
Or it could be a stuck thermostat too.