We had a cheap "frost-free" upright freezer as a long-term store in an empty room. Two days after I deposited the week's milk in it, my wife found the freezer door wide open, the compressor running noisily and the summer's fruit thawed. I'm in the dog house, but...
The door was well balanced; it didn't move if left 90deg open when using the freezer. The door was found 180deg open. Neither of us ever remember opening it that far; there was never any need to.
Examining the machine, we saw that the downpipe at the rear that carried the condensate down to its receptacle had broken away from its outlet, even though it was not vulnerable to damage. No one apart from my wife or I access the room.
We wonder if there is any way that pressure could build inside the freezer and "puff" (blow sounds a bit explosive!) the door open?