It’s air-conditioning time; know the cool basicsWritten by Nick Shultz | | firstname.lastname@example.org
The hot weather has finally arrived, and along with it comes the high humidity associated with this area. I don’t think anyone can ever really get used to the humidity and heat combinations here in Northwest Ohio. It comes upon us, nonetheless, every year about this time. The only real relief is our air-conditioning (a/c) units in our homes, workplaces and vehicles.
All our a/c systems fundamentally operate the same way regardless of what, or where, they are cooling. The refrigerators and freezers in our homes use the same principles of operation as does our vehicles. And although our refrigerators and freezers rarely give us trouble, that is not often the case with the a/c systems in our cars and trucks.
The primary reason for the breakdown of our vehicles’ a/c systems is the harsh environment in which they operate. Unlike the a/c units in our homes, which remain stationary while in use, our cars’ a/c systems are constantly in motion. This constant movement of components and the exceptionally high underhood temperatures in which they operate can cause our vehicles’ a/c systems to develop small leaks. Those leaks bleed the a/c refrigerant into the atmosphere and ultimately cause the a/c system to fail.
This constant bleeding of the refrigerant into the atmosphere has turned out to be a real problem for our environment. It seems the refrigerant we once used (refrigerant 12 or simply R-12) in our vehicles a/c system was destroying the ozone layer of our atmosphere. As the refrigerant bled out of our vehicles, the vaporized refrigerant began to rise. Once it reached the ozone layer, located in the stratosphere, it began to destroy it.
The ozone layer shields you and me, and all of Earths’ creatures, from harmful ultraviolet rays. Those ultraviolet rays come from the sun. Overexposure to those ultraviolet rays can cause skin cancer and cataracts and can kill off vast quantities of our seas’ and oceans’ plankton. Of course the sea’s food chain supply begins with plankton. It is not hard to imagine the consequences to mankind should the sea’s food chain be destroyed.
According to the Environmental Protection Agency, during the life of an air-conditioning system it will leak, on average, 2.3 pounds of refrigerant into the atmosphere. Roughly 40 million pounds of refrigerant leaks into the atmosphere globally each year.
Because of the ozone’s imminent destruction, countries around the world joined together and banned R-12 which was destroying it. Since 1993, all vehicles have used a more environmentally friendly refrigerant called R-134a. Whereas R-12 is chlorine-based, the replacement R-134a is not. Several other protocols for servicing vehicles’ a/c systems were adopted at that time, chief of which is the requirement that all a/c system service technicians be certified in the proper handling, reclamation and repair of any a/c system.
Some a/c fundamentals
Hot always moves toward cold. Never the opposite! It’s one of those physical laws of nature that we cannot break. If we were to stick a large block of ice inside our passenger compartments within our vehicles, then the interior of our cars would cool off quite rapidly.
At least until the block of ice melted. Essentially that is what we do in an automotive a/c system. We stick a very cool component, about the size of a block of ice, within our passenger compartments. We refer to that component as an evaporator. All the heat from the passenger compartment immediately begins to be absorbed by the refrigerant inside the evaporator. The absorption of the heat from within the interior of the vehicle, via the evaporator, causes the refrigerant inside the evaporator to change physical state from a liquid to a vapor.
An interesting byproduct of the normal evaporator’s function is that it removes the moisture from inside a car as well as cools it.
As the heat is attracted to the low temperature of the evaporator core and then is absorbed by the refrigerant inside, the moisture trapped within the heat collects on fins, which are attached to the outside of the evaporator.
Then the collected water pools and drains out the bottom of the evaporator housing, via a hose, to the ground. That’s the water you see dripping under the car on a hot summer’s day.
The textbook definition of cold is the absence of heat. If the heat we are removing from inside the passenger compartment is greater than the heat that is entering from outside the vehicle, then the inside of the car begins to cool down. It does so because with the absence of heat, all that remains is cold. We can break the laws of man, but we cannot break the laws of nature. We can, however, use those laws to our advantage. Such is the case with the a/c system. By removing heat from our cars, what remains is cold. Controlling the amount of heat we remove will control the temperature within a vehicle.
Once the refrigerant absorbs the heat from within the passenger compartment, it is drawn out of the evaporator and into a compressor. Once inside the compressor, the vaporized refrigerants pressure is raised dramatically and pushed out of the compressor pump, through some plumbing and on toward the front of the vehicle. Located in the front of the vehicle, immediately in front of the radiator, is a device called a condenser.
The compressor not only raises the pressure of the vaporized refrigerant, it also raises the refrigerant’s temperature. It raises the refrigerant’s temperature to a point very much above the outside ambient air temperature. Remember, hot always moves to cold! As air is drawn through the condenser, the heat trapped in the refrigerant vapor is absorbed by the surrounding atmosphere, and the refrigerant vapor turns to a liquid. Therefore, hot moved to cold.
The liquid refrigerant is then pushed out of the condenser by the same compressor pump that raised its pressure. It then is forced through a small nozzle that resembles, in function, the nozzle on your garden hose. When passing through this nozzle the pressure, and the temperature of the liquid refrigerant is substantially lowered. The refrigerant then re-enters the evaporator as a low pressure and low temperature liquid. Thus, the whole process begins again.
Now there are obviously quite a few electrical devices and various other gadgets that make the a/c system function properly within our vehicles. Nonetheless, the basic operation is accurately described above. The neat thing about the above description of operation is that our home refrigerators and a/c units work the same way. The only real difference is the switches and other gadgets that control the temperature of those devices.
There is no magic at play in the operation of these a/c systems. It is simply physics at work. Does that make the men and women who service those a/c systems applied physicists?
Most folks could give a hoot about how their a/c systems operate. They are only concerned that those systems do in fact function correctly, especially so when it’s 85 degrees outside with 85 percent humidity.
To ensure the continued normal operation of your vehicles’ a/c systems, and to be a proper steward of our environment, each of us should have our a/c systems serviced on a regular basis. The system should be inspected every couple years by a certified a/c technician.