Although most new homes have ducts and vents already in place, many older homes have old convection heating systems or baseboard heaters without ductwork. In such cases, you will need to install ducts and vents to provide the air conditioning with a flow system. This would be the time to explore upgrading the existing heating system as well, as it will be much cheaper to do together.
An EER certifies the cooling efficiency of HVAC units. It's calculated by the rate of the cooling in British thermal units (Btus) per hour and divided by the rate of energy input in watts at a specific temperature. The calculation goes as BtuH/WATT at dry bulb (db) versus wet bulb (wb) temperatures. The optimal rating for a cooling unit is about 80db/67wb inside and 95db/75wb outside.

Lennox, on the other hand, is probably the most expensive unit out there and I can’t stand them.  In our (humble?) experience, they have a horrible logistics chain, making repair parts difficult to come by (sometimes taking weeks), poor customer service, and the parts cost three times as much. That’s not what this article is about, so read more in: Carrier vs. Lennox Furnace Review.

If you hear clicking that is followed by a hum or buzz, you’re probably hearing the fan motor attempting to start without the boost it needs from the capacitor. You can almost always conclude that the capacitor has failed. Sometimes you can get the compressor fan spinning (clockwise) by pushing it with a thin stick or long screwdriver poked through the grille. But the chances are good that this might work for one cycle, but the capacitor will fail next time the AC goes on. It’s best to replace the capacitor.