it sounds like the coil is freezing up which could happen due to humidity....there is a sensor in there that when it thinks it is happening will cut the compressor off until it thinks the ice melts. You need to check that sensor and make sure it is positioned properly or you will get these false cutoffs...or you might have a slight leak and are low on refrigerant which also triggers freeze ups...if it seems to work fine when temps are in the 80's..look up the freeze up sensor and the proper placement of it.