How Automotive Air Conditioning Works
You’re halted in rush hour gridlock on an August evening. Sweat dribbles from your neck right down your back until your shirt retains it, making a soggy spot among you and the seat. Your legs are either adhered to the vinyl upholstery or prickled by its modest velvet. Your hands feel like they’re going to sneak off the guiding wheel, and you’re grateful your eyebrows are shielding the perspiration from running at you. Indeed, generally.
What’s absent from this image? Car cooling. It’s gotten almost widespread, with 99 percent of all new vehicles as of summer 2010 coming outfitted with it. At the point when it’s missing, we notice.
It’s additionally been with us longer than you may might suspect. Packard created car AC right in 1939, and in 1940 was the primary vehicle organization to offer industrial facility introduced cooling. Obviously, this early framework didn’t have an indoor regulator, yet it was superior to not having anything by any stretch of the imagination. The thought got on, however, and by 1969, the greater part of all new vehicles were sold with cooling worked in. That is excluding the post-retail AC units that could be introduced during the main warmth wave of the year, when the new proprietor lamented his penny-squeezing at the vendor in January.
In the long run, it was resolved that the refrigerant utilized for quite a long time in car AC, known as R-12, CFC-12, or its image name Freon, was harming the ozone layer (it’s a chlorofluorocarbon). It was restricted from being fabricated in the United States and another option, called R-134a or HFC-134a, was needed for all vehicles made after 1996. Presently, any vehicle more seasoned than that should be retrofitted with another framework that can utilize the more up to date, more secure refrigerant.
Cooling has worked essentially similar route for its whole presence: it cools and eliminates moistness from the air. There are three principle parts to the framework – the blower, condenser, and evaporator – that accomplish this, in addition to a couple of different parts to keep the framework running easily. We should investigate each.
1. The High-pressure Side
2. The Low-pressure Side
3. Recharging a Car’s AC
The High-pressure Side
All car cooling frameworks are (almost) shut circles with a high-pressure side and low-pressure side. We’ll begin with the high-pressure side as it leads from the motor to the traveler compartment:
Blower: The blower is a siphon driven by a belt joined to the motor’s driving rod. At the point when the refrigerant is brought into the blower, it is in a low-pressure vaporous structure. When the gas is inside the siphon, the blower satisfies its name. The belt drives the siphon, which puts the gas under tension and powers it out to the condenser. Blowers can’t pack fluids, just gasses. You’ll see as we experience the framework that there are different parts whose work it is to catch any water that inadvertently makes into the AC circle.
Condenser: The condenser is essentially a radiator, and it fills a similar need as the one in your vehicle: to transmit heat out of the framework. The refrigerant enters the condenser as a pressurized gas from the blower. The way toward pressurizing the gas and moving it to the condenser makes heat, yet air streaming around the curving containers of the condenser chill the refrigerant off until it shapes a fluid once more. Envision steam chilling off and gathering once again into water, and you have the thought. The fluid refrigerant is currently a high-constrain fluid and almost prepared to cool the vehicle.
Collector Dryer: But first, the refrigerant should be prepared for the evaporator. As it moves out of the condenser, the fluid experiences a little store introduced in the line. This collector dryer contains desiccants, little granules that pull in water. You’ve seen parcels of desiccants in shoeboxes, where they do something very similar: pull in water from the air to keep new shoes new and prepared for your feet. (They’re normally marked “Don’t eat.”) In the collector dryer, they eliminate any water that has entered the framework. In the event that the water is permitted to remain and perhaps structure ice gems, it can harm the cooling framework.
That is sufficient high-pressure for anybody, so how about we proceed onward to the low-pressure side of the framework.
The Low-pressure Side
Thermal Expansion Valve (TXV): Here, the system changes from the high-pressure side to the low-pressure side. If you were to touch this part of the system, you’d feel it change from hot to cold.
The high-pressure liquid refrigerant flows from the receiver-dryer through the expansion valve, where it is allowed to expand. This expansion reduces the pressure on the refrigerant, so it can move into the evaporator. The valve senses pressure and regulates the flow of refrigerant, which allows the system to operate steadily, but the moving parts of the valve can wear out and sometimes require replacement.
Some vehicles have an orifice tube rather than an expansion valve, but it serves the same purpose in allowing the refrigerant to expand and the pressure to be lowered before the liquid enters the evaporator. The orifice tube allows refrigerant to flow at a constant rate and has no moving parts, but it can become clogged with debris over time. Systems with an orifice tube automatically turn the AC system on and off to regulate the flow of refrigerant to the evaporator.
Evaporator: This is where the magic happens. While all the other parts of the system are located in the engine compartment, this one is in the cabin, usually above the footwell on the passenger side. It also looks like a radiator, with its coil of tubes and fins, but its job is to absorb heat rather than dissipate it.
Refrigerant enters the evaporator coil as a cold, low-pressure liquid, ideally at 32 degrees Fahrenheit (0 degrees Celsius), which is why you don’t want any water in the system. The refrigerant doesn’t freeze at this temperature, but it does have a very low boiling point. The heat in the cabin of the car is enough to make the R-134a in the evaporator boil and become a gas again, just like water turning back to steam. In its gaseous form, refrigerant can absorb a lot of heat.
The gas moves out of the evaporator — and out of the passenger compartment of the car, taking the heat with it. A fan blowing over the outside of the evaporator coil blows cool air into the passenger compartment. The refrigerant in gas form then enters the compressor, where it is pressurized and the whole process starts all over again.
If the system uses an orifice tube, there will be an accumulator between the evaporator and the compressor. An orifice tube sometimes lets too much refrigerant into the evaporator and it doesn’t all boil. Since the compressor cannot compress liquid, only gas, the accumulator traps any excess liquid before it can get into the compressor.
The evaporator also takes humidity out of the air in the car, which helps you feel cool. Water in the air condenses on the evaporator coil, along with dirt and pollen and anything else floating around in the cabin. When you stop the car and see water dripping underneath, it’s probably the water from the AC evaporator and nothing to worry about.
We’ve all heard about “recharging the AC,” so we’ll take a quick look at that next.
Recharging a Car’s AC
The vast majority of us begin seeing promotions in the spring for vehicle fix shops offering bargains on reviving your vehicle’s cooling as expected for the coming summer. Which causes us to ask, what is energizing the AC? Is it required, similar to an oil change? Does my vehicle’s cooling should be energized? Is this another trick that fix shops can pull on clueless clients?
The response to that last one is certainly no; reviving the AC isn’t a trick. It just implies that new refrigerant is added to the framework. On the off chance that the refrigerant is somewhat low, it very well may be finished off, equivalent to on the off chance that you were somewhat low on oil in the motor. On the off chance that it’s extremely low, however, whatever refrigerant is as yet in the framework should be emptied out and supplanted. This cycle of getting out the framework and adding new liquid is called energizing.
In one or the other case, you’ve lost some refrigerant, which isn’t so incredible. Despite the fact that R-134a is preferable for the climate over Freon, the Environmental Protection Agency would prefer not have any cooling refrigerant spilling into the dirt and streams. In case you will have the framework depleted and revived, the EPA suggests having the specialist investigate the framework to discover the wellspring of the break and fix it. They don’t need the fix, however they’d ridiculously like you to have it done.
This article has rambled about R-134a as a swap for large, awful Freon, yet there are others that have been affirmed by the EPA, as well. R-134a has the qualification of being the refrigerant generally tried and suggested by producers, yet there are others with names like Free Zone, Freeze 12, and Kar Kool that the EPA will permit in car cooling frameworks [source: EPA].