UPDATE 7/9/14: Went back to the shop and scolded the manager. After another round of soap bubble leak checking and even checking with nitrogen gas (not sure what that's for), he finally said something similar to what my first mechanic said, i.e. that my pressure valve (was it 'valve' or something else? can't remember) might be relieving the gas due to high pressure that's why it all leaves the system so suddenly. Therefore I'm getting more and more convinced that it's not in fact a 'leak' per se. A leak would mean GRADUAL decline in cooling effect right? In my case it runs very well and very cold for about 3-5 days after refilling gas, then all of a sudden next day I start my car and it's just blowing hot air because the gas is not there any more.
Anyway he refilled the gas for free and asked to drive around for 3 days and get back to him and he'll check if there's any gas leaked out or gone completely so he can do further diagnosis.
Any opinions? Any significance in the fact that the loss of gas is not gradual, instead seeming to be very abrupt?
Drillz of my car: