Buying an air conditioner is not like buying a car. Your car is assembled at the factory and each dealer gets the same quality for that make and model while your air conditioner is shipped to the dealer in to be assembled by the contractor at your house.
If each car dealer had to assemble your car the way each air conditioning contractor has to assemble your cooling system you would be a lot more careful when choosing a car dealer. It would be very important that the car dealer you chose knew how to assemble the car properly.
The same is true when buying an air conditioner. It must be sized accurately and installed correctly to work properly, This may include making changes to the existing ductwork to ensure adequate air flow.
In the 40 years I’ve been in the heating and air conditioning business it has been my experience that 75% of the problems with new central air conditioners were caused because they were not sized accurately and were not tested correctly after they were installed.
In any air conditioner less than five tons was classified as an appliance and people working on them did not require a licence or mandatory training. People learned from the boss who little or no technical training available to him. Five years ago residential air conditioning became a two year apprenticeship trade but it will take time for things to change.
It is important that the contractor have the air conditioner checked by a licensed mechanic during and after the installation to ensure the work is done correctly. Don’t try to save money on the installation because you will pay for it later.