I read all these post and feel like I should tell you to call a service technician. If your anywhere near anchorage ak I will come and take care of your problem. Seriously though check to see if your condenser coil is clogged and if that's not the case shut the unit off and call a technician. Letting it continue to run the way it is could eventually ruin your compressor. Sounds like to me it is either shutting off on low pressure or high head pressure. If your condenser is clogged that would make it shut off on high head. You could also have a refrigerant restriction past the condenser, or a leak and the system is badly undercharged. Is the evaporator (inside the box) icing over. Is their plenty of airflow inside the cooler etc.