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Please comment and/or add your thoughts to this discussion as related to explaining a system to a student or customer.
The Thermostat
A thermostat is a temperature-sensitive device, which is a crucial part of an air conditioning system. As inside air temperatures rise above or fall below a preset limit, the thermostat tells the air conditioner when to turn off and on to control them. Operation can range between simple, manually operated devices to sophisticated programmable units with enhanced functionality and Wi-Fi capabilities. The thermostat is often placed in close proximity to the air handler. Ideally, its location is in the center of the house away from windows, doors and high-traffic areas. Direct sunlight or constant drafts from an opening door can have adverse effects on its operation. This can lead to false temperature readings and the cycling of your air conditioning system, which will burn through more energy and raise your utility bills.
Condenser and Compressor
An air conditioning system utilizes refrigerant to cool your home. The air conditioning components work in unison by converting the refrigerant from a liquid state to a gas vapor state and back to a liquid state again. The process takes the refrigerant through stages of saturation (exists in both liquid & vapor) to superheated vapor and subcooled liquid.
The compressor and condensing coil are located outside your house. A typical configuration for this component would have the compressor mounted to a base and surrounded by the condensing coils and cooling fins. They can be noisy and are often placed in areas away from bedroom windows and patios.
As the refrigerant superheated vapor arrives at the condensing unit, a compressor squeezes it, which creates an extremely hot and high-pressure gas. Next, it travels to the condenser where cooling fins positioned around the condensing coil help to dissipate or remove the heat, thereby converting it into a saturated liquid.
Evaporator and Air Blower
Next, the condensed refrigerant liquid travels to the evaporator and coil inside the air handler. As the liquid enters the metering device and then the evaporator coil, its pressure is reduced. This is where the magic begins. Since heat is required to separate the molecules to convert the liquid back into a gas, it draws the heat from the surrounding air. Metal fins positioned on the evaporator coil help with the heat exchange during this process. As the refrigerant leaves the evaporator, it is a cool, low-pressure gas. It travels back to the condensing unit and the process repeats itself over and over again.
The evaporator coil usually resides inside an air handler or as part of a furnace heating system. The air handler is a housing that contains the evaporator as well as a fan and blower assembly. The fan/blower assembly is responsible for directing the airflow across the evaporator fins. As the warm air crosses the evaporator fins, its heat is extracted, which converts the liquid refrigerant back into a gas as part of the process mentioned above. The cooler air is then forced into a series of ducts and distributed to vents located throughout your home.
The entire process continues until the inside temperature reaches the programmed settings on a thermostat. Once the thermostat senses the desired level has been achieved, it deactivates the air conditioning system. As the temperatures inside your home rise above the programmed settings on the thermostat, the system is reactivated to cool the air.
Things to Consider
The above information is a basic explanation of how an air conditioning system works.