Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.