It's all pretty straightforward stuff...commonsense basic electricity and mechanicals. Clean coils are a must...nothing piled around the condenser. If you're needing to add refrigerant, then you have a leak that should/must be fixed because these are hermetic (sealed systems). Another important thing to be aware of is the condition of the ducting in your attic. Leaks there will cost you big $$$ and are tough to detect without a visual inspection..unless you feel cold air coming out from around a wall outlet or switchplate.

Leathermang and I know all about thermostats and incorrect wiring diagrams, don't we Greg?

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Never a dull moment at Berry Hill Farm.