Random scenario.....someone gets an AC unit installed 7 years ago by...

Random scenario.....someone gets an AC unit installed 7 years ago by a local A/C repair company. Local A/C company was responsible for registering the unit for the 10 year warranty. Local company never registered it, which brings the warranty to 5 years. Unit breaks after 7 years, so it's not under warranty because local company neglected to register the unit. What's the recourse for the homeowner?