Improper installations will affect system operation, efficiency, and capacity.
The brand you purchase has to be installed properly to function.
Even mediocre installations could, over time, result in a major break down that could happen months after the system is installed
Your duct system matters. According to Jack Bartell, York International, improperly installed flex duct can have the short-term result of not providing enough heating and cooling to a space, there are long-term problems to watch out for as well.
Your system operates at less than expected airflow across the evaporator, it will result in a lower coil temperature. "This, in turn, leads to frost on the coil, which causes more restriction to the flow of air and leads to more frost," stated Bartell. "This snowball of cause and effect leads to a loss of capacity, so the thermostat cannot satisfy the demand for cooling. This results in a long-run cycle with little or no effect on comfort, along with an enormous waste of energy."
The most serious result of low airflow in cooling mode is how it affects the compressor.
If your HVAC Professional didn't ask questions or look at your duct work when they completed their on-site visit, they might not have your best interest on their mind.
This diagram explains how a system is connected to supply ducts, return ducts, and refrigerant tubing.