That is a personnel decision. The setting is to introduce fresh outside air, in the other setting it recirculates the air from the inside of the house, this is more efficient,
no
low on gas would not work at all
the unit set temp may be close to the room temp
There is about 5 degree + or minus around the temp setting so if you have it set for 20 C and the room or ambient temp is 22 C that would be one reason for the short cycle
of course you could always get in a technician for a proper diagnosis