Having explained to my customer that the most likely reason for the fridge not running was, a shortage of refrigerant, I proceeded to look for a leak ! some 30 seconds later my customer came rushing back in to the sound of me pissing myself laughing. I found that the suction service port on the small can, still had the rubber plug in it or rather, used to. The give away sign was the oil up the wall and ceiling, leading from the port. What really astounded me was when she explained the unit had been running satisfactorily for years. And only faulted due to being located in the sun and turned off at night , pressure temprature relationships go figure !