To recharge a Trane air conditioner, attach a can of refrigerant to the charging manifold, attach the charging manifold to the liquid line service valve, and open the regulators until the unit reaches the proper pressure. If possible, this process should be performed by an HVAC technician.
Refer to the Trane air conditioner model's user manual to find the right type of refrigerant to purchase for the unit, and gather an air conditioner charging manifold. Turn off the compressor before hooking the manifold's yellow hose to the refrigerant, opening the regulators slightly on the canister and the other two hoses to purge the air. Close the regulators, and attach the hose of the plain pressure gauge to the unit's liquid line service valve.
Open the regulator on the plain pressure gauge's hose slightly before opening that of the refrigerant canister, and close the latter when the gauge shows the desired pressure for the Trane air conditioning unit. Turn on the appliance, and check the subcooling. If the subcooling is inadequate, open the regulators again and repeat the process. Close all regulators before disconnecting the hoses. Never attempt this process without using the proper tools as the pressurized refrigerant canister can pose a safety hazard.