I'll see if it gives me any more trouble. The ice buildup was on the right hand side, bottom to top and several inches wide & thick. So I put thermostat in the middle of where ice block had been, figure the thickest part will have to be completely melted before thermostat turns off.
I thought thermostat was supposed to cycle on and off to maintain an optimum defrost temperature, but original (and replacement) won't turn back on until below 32F, next cooling cycle. The others I've seen L140-30F would run much hotter and could cycle.
I've had this unit since the late '90's, no issue (except hair on cooling coils) until just a couple years ago. Maybe the defrost thermostat failed; that's what I thought and replaced it one year ago. Think it was between upper & lower coils toward the left.
Air enters compartment top rear and exits bottom front, passing between freezer and fridge. Previously I could feel ice there.
Wasn't down to temperature last night but compartment has now reached 15F, have put frozen items back in now.
This GE unit appears to have retained (at least most of) its refrigerant, uses good old R12.
My Frigidaire deep freeze started melting things at half the age of this one, needed recharge of R134A.