Air conditioners lower indoor air temperatures by blowing cool air directly from the unit instead of through ducts. Also called AC units, air conditioners are used as a main source of cooling or for spot cooling areas where central air systems are insufficient. They make areas comfortable for people to reduce the risk of heat-related illness and help protect computers and machinery from heat damage. Ductless split systems can be configured to cool multiple rooms from a single compressor. Evaporative coolers are suited for dry climates since they bring in outside air to cool and humidify it. Portable AC units can be moved where needed. Window, wall , and ceiling AC units cool a single room without taking up floor space. Packaged terminal air conditioners and heat pumps provide heating and cooling from a single unit. Air conditioner accessories include chemicals, tools, and testers for maintenance, cleaning, and recharging.