I haven't looked at a detailed view of the wiper assembly on the xfire but most cars use a single motor that drives both wiper arms. The motor is connected via mechanical linkage to each wiper which operates them in unison. If only one side is working the other arm is in someway disconnected. The disconnection could be where the wiper arm attaches to the drive spindle located below the lower edge of the windshield. If the wiper arm has been improperly installed to the drive spindle, or is not the correct size, or has been damaged this could be the cause for not working. If the drive spindle is oscillating back and forth with the arm remaining stationary one of the previously indicated conditions could be the cause. If this is not the cause then a deeper look into the drive system as suggested needs to be made.