Addressed an issue with a Trane XR15 air conditioner that was not cooling and making a clicking noise. Diagnosed the problem as a faulty contactor and low refrigerant levels. Replaced the malfunctioning contactor to resolve the clicking noise. Located and repaired a refrigerant leak in the evaporator coil, then recharged the system with R-410A refrigerant. Checked system pressures and tested for optimal superheat and subcooling values. Ensured the unit is now cooling effectively and operating quietly.