There are several pressure testing methods used in HVAC refrigeration systems, including air pressure testing, nitrogen pressure testing, and hydrostatic testing. Air pressure testing is a low-cost method that uses compressed air to pressurize the system, while nitrogen pressure testing uses nitrogen gas to provide a more accurate test. Hydrostatic testing, on the other hand, uses water or a non-reactive fluid to test the system’s integrity. Each method has its own advantages and limitations, and the choice of method depends on the specific system requirements and safety considerations.