Completed an AC repair on a Lennox XC21 unit. Diagnosed the issue as a malfunctioning capacitor and low refrigerant levels. Replaced the faulty capacitor with a new Lennox OEM part and recharged the system with R-410A refrigerant using a Yellow Jacket manifold gauge set. Cleaned the condenser coils and checked the thermostat for proper operation. Verified that the system is now cooling efficiently and maintaining the desired temperature. The unit is back to optimal performance.