We just moved into an 11 year old house last month. The AC has not worked properly since we moved in. The first AC guy the Homeowners Warranty company sent cleaned the unit and added freon. A month later, it was 83 degrees downstairs today. Last week they sent another guy and he found what he says that the system is mismatched. The warranty company is claiming that they will not cover this because the system is mismatched... a 4 ton evaporator coil with a 3 ton condenser.

It seems like to me that they are trying to get off the hook. HELP. I need someone to explain this to me.

This mismatch of coils to condensing units are done all the time and it will do a better job of dehumidification and in some cases a higher efficiency, some manufacturers match a larger coil to achieve a higher SEER rating Goodman air conditioning did this with there equipment and Carrier has a coil that is used for two or three ton systems (same coil) And a single coil for either four or five ton systems.
A coil that has a thermostatic expansion valve would be preferred.
You probably have a problem and they are dumb founded because they can't find the real problem, so they tell you this. Good luck, Mike