To replace an evaporator coil in an air conditioner, remove the old coil, insert the new one in place and recharge the coolant. Once the coils have been replaced, test the air conditioner to ensure the repair is sufficient.
Before replacing the air conditioner evaporator coil, inspect the area. If the coils are damaged or cracked, they do need replacing. Disconnect the unit from electricity and use a small pipe cutter to cut the inbound and exit tubes. Place electrical tape over the cut inbound and exit tubes to prevent debris from going inside, and then pull the evaporator coils out.
Put the new coils in place of the old ones, lining them up with the existing ports. Remove the electrical tape and wipe off the tubing to further remove tape glue. Align the new coil tubing with the inbound and exit tubes, and use a soldering iron to seal them together.
Use a vacuum placed at the beginning of the lines to remove any air from the piping. Set the vacuum to suck air, not blow it. Once the air is removed from the piping, check the coolant levels. If necessary, replace lost coolant with the fluid recommended by the air conditioner manufacturer.
Reconnect the unit to electricity and switch it on. Set the thermostat to the cool setting, and lower the temperature. The air conditioner should start up and blow cool air.