Final answer:
Both Technician A and B are correct; a squeal on compressor clutch engagement could be due to either a loose serpentine belt or a worn clutch pulley bearing.
Step-by-step explanation:
If a squeal is heard only when the compressor clutch first engages, the cause could be either a loose serpentine belt as suggested by Technician A or a worn clutch pulley bearing as suggested by Technician B.
A loose serpentine belt can slip on the pulleys and make a squealing noise when the belt's grip is suddenly tested, such as when the compressor clutch engages. On the other hand, if the clutch pulley bearing is worn, it may also produce a squeal upon the clutch's engagement due to increased friction and misalignment. Therefore, the correct answer is C. Both Technician A and B are correct.