Before you install a new air conditioning system, consider your home's electrical system. It's not uncommon for old houses to have only 110-volt, 60-amp service for the entire home, barely enough power to handle the home's existing complement of lights and appliances. Central air conditioners require a dedicated 230-volt circuit and may require 20 to 50 amps of power, making an electrical service upgrade necessary. Have an electrician size your home's electrical supply up before your HVAC contractor begins work.
You can attach a length of soft copper tubing to extend the reach of a blow gun nozzle used with an air compressor. The extra length will allow you to clean out motors and interior machine parts without getting a face full of dust. The end of the tubing can be bent to reach around the back side of motors or into other hard-to-reach areas. Use a wet/dry vac along with the blow gun to help keep dust out of the shop.