AC cooling changes

There are 2 possibilities. The AC unit may be changing temperature. This may be caused by the compressor cycling on and off or there may some restriction in the system that is getting stuck somewhere and restricting refrigerant flow. When it breaks loose the system get cold, when it get stuck the system warms up. The other possibility comes from the air delivery system. The AC system makes the cold, the air delivery system delivers the cold air to the passenger compartment. If the temperature blend door is moving unintentionally the temperature in the cabin will move from warm to cold and back again. Sounds like you need to consult a shop that knows AC