First, check the thermostat location...is it in close proximity to the main return air grille? Be sure it's not in direct sunlight, on an outside wall or that a supply register is not blowing air directly at the thermostat. If these things are correct, the most likely reason for short cycling at the lower temp range (ambient)would be that the system is oversized...the most common mistake in installations,no contractor wants to be caught installing an under sized system he has to replace free and they usually over size. If the unit is too large, it can't run long enough to remove moisture from the air hence it will short cylce because it's cooling the air too soon not actually conditioning the entire structure. I hope this helps.