Air-conditioning service, in many ways, is different than service to other parts of the vehicle. Although there are few parts in the system (Figure 51-1), each component has a specific purpose and service procedure. That in and of itself is not a big deal. The challenge with air-conditioning is how it operates. The system operates on changes of refrigerant pressure. Many things can cause the pressure to changes; some are part of the system, some are part of the environment, and some are faults or bad components in the system.