The AC unit in my house is 25 years old, and it's not big enough for the size of our house, it is also not very energy efficient. We have a home warranty that we got when we bought our house and it’s due to expire in a couple of months. Is there something we can do to “break” the compressor so the warranty replaces it?

I do not recommend trying that. Insurance fraud is a Federal offence with jail time.

WoW! That's crazy! How exactly do you know the system is undersized?