frosty
Ok, first it would be nice to know how big your house is, and how big your portable a/c is. It sounds to me like the compressor is shutting off on a pressure switch or its own internal overload. If your A/C unit is small and you have an average size home, your probably working the machine to death. Now an air conditioner is meant to "cool" the air. It sounds to me like you want a walk in cooler. It is very hard for any air conditioner to get the home below 70 degrees. Air conditioning is considered high temp refrigeration. Design specs for all central a/c's is for an outside temperature at 95 degrees and an indoor temp of 75. Thats a 20 degree temperature difference. Now it is possible for a/c's to get the house to 70, but your going to be working the thing very hard, especially if your undersized. Now if your like most of the country right now, and getting around 100 everyday, and trying to get the house below 70, thats a 30 degree temp difference, and your beyond the design specs of the unit. The compressor gets overheated from never shutting off and shuts off on an internal overload. OR, if your setting the machine that has a digital control, which sounds like you do, you could also have a bad thermister, that is what is controlling the temperature for your machine. Simple ohm tests will let a person know if its getting faulty. But my main concern is that it sounds like you want to cool the house lower than 70. Thats a tall order for any a/c to do when it is scorching hot outside. If you do want your home below 70, you will need to purchase more a/c's to do some of the work.

talon699
Check your manual, it may be preset at the factory for 70. Is the unit large enough for the room? 10.000 btu for approx 300-350 sq ft? Is the water tank full, and needs to be drained? Is your vent pipe within the limits. If the exhaust is too long the unit will not work properly .

AC_mechanic
I don't know how cool you like it, but 70° is pretty good. It's natural for it to have a bit of a differential. It could have a low limit setting in the thermostat of 70°. Read the book. My question to you would be this: If you set it at 80°, will it still turn back on at 72°? If it goes up to 80°, then I would say it's a good chance that your thermostat has a low limt of 70° in the AC mode. You may be able to override it. It may have a high limit default setting of 80° in the heating mode. You have to read the manual for the thermostat, but I would say in this kind of weather your air conditioner is working pretty good if it keeps yor house at 70°. Finally, it could just be a broken T-Stat. If all else fails just replace it. You could jump the t-stat out. If your house get's below 70° then your AC is rocking and rollin. Just be careful not to F*** anything up. LOL

mountainriley
No ac is designed to maintain 63. Sounds like the ac is smarter than you are.