Whether the unit is being repaired or a new air conditioner is being installed, the repair person will apply their hourly rate, transportation costs, and any materials that were needed to service the unit. The invoice should only be sent when the unit has been repaired successfully to the satisfaction of the client. The invoice will list all repairs and materials used with the associated charges labeled next to them. The total amount due will be written at the bottom of the statement along with the date upon which the amount must be paid.