## 4 Results and Discussion
### Pareto Analysis of HVAC System  
The Pareto chart for the fifteen subsystems (refer to Table 2) of the analyzed HVAC system is shown in Figure 4. It depicts the components' failure frequencies and percentage contributions to the failures of the HVAC system. It is observed that the AEFS is the most critical subsystem, and it contributes 27.79% of the total failures. The BFS is the second most critical subsystem and contributes nearly 21.78% of the total failures. Nearly 50% of the total failures are due to AEFS and BFS; therefore, they are the most critical subsystems. This significant contribution underscores the importance of prioritizing these subsystems in maintenance schedules and quality improvement initiatives. The AGLAJ (10.12%), ACC (9.17%), AHCL (6.88%), BR (6.59%), and HCP (5.73%) are responsible for nearly 38% of the total number of failures. Therefore, these components require moderate attention and inspection schedules should be prepared accordingly. Each subsystem contributes between 5 and 10% of the total failures and is considered a moderately critical subsystem. The HHC, ACFS, RM, AERS, WM, APS, and BS are the least critical subsystems, as they rarely fail. Maintenance for these least critical subsystems can be deprioritized to allocate resources toward more failure-prone areas. This targeted approach can streamline maintenance, reduce downtime, and enhance overall HVAC system reliability. A detailed analysis of the most and moderately critical components is required to be carried out. The detailed Pareto chart for these components is presented in Figures 5-10. Figure 5 presents the Pareto chart of the A/C evaporator front side (AEFS). It shows that the leakage has the highest failure frequency, contributing 97% to the total failure percentage with a failure frequency of 94 times. Core assembly issues and anti-freeze sensor defects are the other observed failure modes that rarely occur. The Pareto chart for the failure modes observed in the blower front side is shown in Figure 6. It shows that the motor is the most critical component and contributes 89% to the total failure percentage with a frequency of  
Figure 4: Pareto chart for the subsystems of the HVAC system. 68 times. The faults in writing are the other observed failure modes, contributing nearly 11% to the complete failure percentage. The Pareto chart of AGLAJ, shown in Figure 7, shows that the leakage is the most critical failure mode and contributes 80% to the total failure percentage. The valve pin, charge valve, pipe joint, and expansion valve are the minor failure modes that cause the HVAC system to fail. Figure 5: Pareto chart of the A/C evaporator front side. Figure 6: Pareto chart of the bluer front side. Figure 7: Pareto chart of the A/C gas leak at joint. Figure 8 shows that the compressor pulley, belt, and hub assembly fail most frequently, and its contribution is nearly 63% to the total failure percentage. Similarly, coil failure has moderate failure frequency, contributing 25% to the total failure percentage. The compressor and weak compressor leakage are some of the other failure modes observed in the ACC subsystem. From the Pareto shown Figure 9, it is observed that leakage has the highest frequency of failure, which is 22 times, and has a total failure percentage of 92%. Ring failure and assembly error have the same failure frequency, which is 1 time. The total individual percentage of failure of these two components is 4%. The Pareto shown  
Figure 8: Pareto analysis of the A/C compressor. Figure 10: Pareto chart of the HVAC control panel. Figure 9: Pareto chart of the A/C hose cut/leaking. in Figure 10 shows that assembly internal failure due to vibration has the highest failure frequency, contributing 70% to the total failure percentage with a frequency of 14 times. Figure 11 shows that internal failure in assembly has the highest failure frequency, contributing 78% to the total failure percentage with a failure frequency of 7 times.