If the unit must go in unconditioned space, ensure that the space is well insulated. Outdoor units should be placed out of the sun and kept free of debris. Also:
Your system efficiency can be increased as much as 20% by properly sizing, sealing, and insulating ducts. This can also provide more uniform heating and cooling of all of the rooms in your home.
Your contractor should be able to test your duct system to identify leaks and fix them with quality duct sealant. Ensure that the duct system is not only sealed, but within conditioned space. If the ducts must be in unconditioned space (basement, attic, crawlspace) they should also be insulated.
More information on duct installation; determine whether your home is a good candidate for duct sealing.
The test consists of measuring the airflow at the indoor coil, a component that is installed in the ductwork at or near the furnace or air handler that heats or cools the room air. System testing and any necessary adjustments should be done after duct leakage repairs have been completed.
If airflow is too high, duct leakage increases and the temperature at the register is not sufficient for optimal home comfort.
If airflow is too low, distribution efficiency drops ands accelerates the wear on system components leading to premature failure.
Recent field studies suggest that approximately 75% of installed cooling equipment may be improperly charged. Improper refrigerant charge can lower efficiency by 5 to 20% and can ultimately cause premature component failure, resulting in costly repairs that could have been prevented. Recent field studies suggest that approximately 75% of installed cooling equipment may be improperly charged.
Since 1992, in order to protect the ozone layer, all technicians who work with refrigerant in cooling equipment must be certified to handle refrigerant. Ask for their certification for refrigerant handling.
The contractor should always follow the manufacturer's installation instructions to prevent unnecessary furnace or air conditioner on/off cycling.