First thing I'd check is the hydro supply to your RV. Test voltage at both times and see if it is the same. You can even buy a plug in tester if necessary, that plugs in to receptacles. It may be a case of everyone around you has AC etc on during the day and your incoming voltage has been lowered, thus AC will not work correctly, and at night when some others are off, your voltage comes back up to where AC will function properly. Especially likely if you are near the end of a power cable run. If you have access to a good generator even temporarily, try plugging into that during the day and see if it doesn't make a difference.