There are several types of flushing methods used in refrigerant system cleaning, including liquid flushing, gas flushing, and vacuum flushing. Liquid flushing involves using a liquid solvent to remove contaminants, while gas flushing uses a compressed gas to blow out debris. Vacuum flushing uses a vacuum pump to remove contaminants and moisture from the system. The choice of flushing method depends on the type and severity of contamination, as well as the system design and components.