How Air Conditioners Work

Every time I ask someone to explain how the refrigerant cycle works, they begin with what’s going on with the COMPONENTS of the refrigerant cycle and I immediately am left with the “duh??” thought and I get frustrated because I get left behind. So here goes the way a commoner like myself comes to grip with understanding the refrigerant cycle.

I have been “thoroughly” educated but NOT in chemistry or physics. I am told it’s all about an evaporation process and immediately I start applying what I know about water. Big mistake… So how do you make something that doesn’t make sense to most of us easy to understand? I don’t think it is possible to make it easy to understand. I hope this article makes it EASIER to understand without delving into physics, thermodynamics, or an engineering appreciation of the components of the cycle.

How does the refrigerant cycle work?

So, let’s begin at a beginning:In a closed refrigerant circuit, there is a direct relationship between temperature and pressure. If temperature INCREASES, so does the pressure.  If the pressure DECREASES, so does the temperature.If there are any doubts about these two statements, you will have to go to a physics book or a very elementary book on thermodynamics.  Refer to the above paragraphs.  Please trust me on this beginning premise.

Air conditioning is all about increasing the pressure of a gas (the refrigerant, in this case R410a) and releasing the pressure at strategic places along a closed refrigerant circuit. Air conditioning is all about the pressure changes that are forced to occur within the refrigerant circuit.

The example I have chosen to illustrate is a split system air conditioner with the indoor component located in an attic and an outdoor system installed beside a house. I have chosen to identify the component located in the attic as the air handler.  The air handler contains two critical components of the refrigerant cycle, an evaporator coil and a blower/fan (Not shown). Refrigerant lines are connected from the outdoor system to the air handler.

However, with the typical refrigeration system diagrams I have seen, the diagrams assume the reader  knows where the components of the refrigerant cycle are actually located.

Don’t’ be concerned about the dashed line in the diagram YET. The top right portion of this diagram refers to those areas under “high” pressure. The bottom left portion of the diagram refers to those components with “low” pressure

The tx expansion valve, evaporator coil, and blower (or evaporator fan) are contained in the air handler and located in the attic,

Let’s start with the low-pressure portion of the circuit. There is a “ tx valve” that is connected to the small copper tube that connects to the evaporator contained in the component described as the “air handler”.

The valve causes a significant reduction (pressure drop) to the pressure contained in the small copper tubes that disperse the refrigerant through the coils of the evaporator. (Can you picture the effect of pressing the valve of an aerosol hair spray container?)

This forced pressure drop causes the temperature to cool the copper/aluminum coils contained in the evaporator coil. The fan (blower) propels air from the return air flows of the air conditioning system to pass through the coils of the evaporator. The air that passes through the evaporator (propelled by the fan) is significantly warmer than the copper/aluminum tubes. The heat transfer from the cool coils warms the gas that is in the cool coils. The heat transfer that results, forces the air to be significantly cooler than it was before the air entered the evaporator and the cooled air cools the conditioned space.

Now note the upper, right side of the diagram.  The compressor, condenser and the condenser fan is located in the outdoor system.

Now note the upper, right side of the diagram.  The compressor, condenser and the condenser fan is located in the outdoor system.

After the refrigerant is has passed through the evaporator the refrigerant flow is directed

back towards the compressor by a suction pressure in the larger of the 2 copper tubes. The compressor (the component of the system that produces high pressure compressed gas), contained in the outdoor system works to increase the pressure of the gas.

The highly-pressured gas enters the tubes in the condenser coils. The outdoor condenser fan forces air through the condenser coils and cools the high-pressured gas causing the high-pressure gas to become a lower pressured liquid. The heat that is transferred to the air stream created by the condenser fan blowing on the hot coils, decreasing the temperature of the refrigerant, is rejected into the outdoor air.

After the refrigerant travels through the condenser coil, the refrigerant leaves, but pressured as a lower pressured liquid. The refrigerant is now ready to make another pass the “tx valve”.

You may call this cruel and unjust punishment but now I am going to ask you to re-read the paragraphs again, but before you do, I am going to ask you to think about “what’s happening”. The air being “blown” by the fan in the air handler should be the approximate temperature as the desired temperature setting on your thermostat, somewhere between 70 and 78 degrees. So, the air being blown into the air handler is much warmer than the temperature that is produced on the copper/aluminum coils in the evaporator, cooled by the depressurized refrigerant.

As the air passes by the evaporator coil, heat is absorbed into the refrigerant and cools the air to a temperature much cooler than your desired temperature setting (approximately 60 degrees F). The conditioned air should be cooled sufficiently to satisfy the temperature setting on your thermostat so that your system will eventually “cut-off”

No, no, no … don’t stop reading yet!  Now consider what’s happening outside at the outdoor system. The outdoor temperature is cooler (even though it may be 95 degrees outside) than the temperature of the air that is being exhausted by the “condenser” fan. This outdoor temperature difference provides for the exhaustion of the heat in the refrigerant that was captured while the refrigerant was in the evaporator coil in the air handler located in the attic. Heat is being rejected (by the condenser fan blowing air through the aluminum/copper coils in the condenser) from the indoor air to outside air. Now go back and re-read the paragraphs explaining the refrigeration cycle:

The dashed line that is placed in the diagram is there to identify the “high” pressure areas of the circuit as opposed to the “low pressure areas of the circuit.

So far, I have made an attempt to explain the air conditioning (cooling) cycle.  Those of us in the industry may reference these types of systems as “air conditioners”, “air conditioning only”, “AC Only’, or “straight cooling systems”.  Because of where we live, if natural gas heating was more prevalent, you would hear “air conditioner” more frequently because heating could be supplied with a natural gas furnace. If we were to install a system that heats with gas, we would reference such a system as an “air conditioner with a gas furnace”.  Notice that none of these references include a “Heat Pump”?  Because of the limited availability of natural gas pipe lines, and the capability of heat pumps to heat very economically in most or our winter weather scenarios, homes in the Myrtle Beach area are heated with HEAT PUMPS.

Hopefully you have an “oh, now I understand what’s going on moment but I have no idea why this is occurring.”  Because I am attempting to explain at a simplistic level and keep the physics and thermodynamics out of my explanation, my explanation of the air conditioning (cooling) cycle concludes. After many years of selling and promoting heating and air conditioning systems, the light for me has now come on and I now possess a very basic understanding of air conditioning systems.  I strongly suggest letting the engineers and the technicians understand more about the “why’s” of the refrigeration cycle.  I don’t think there is many of us that feel the need to know more.   And there is only a few of us that care to know this much!

If you want to read about the differences contained in a HEAT PUMP, you will find those here.

I want to give credit where credit is due.  I had assistance writing my article.  I discovered a page from $mart Energy User that was used for me to gain the understanding of the condenser.  I actually “borrowed” the graphics, Typical Refrigeration System, from this article.  I also discovered another article that that was helpful to me in understanding the refrigeration circuit.