Basic Automotive Air Conditioning Training
How does your car aircon work?
- Just about every modern car, truck or SUV sold these days comes with air conditioning. It's so common that most people take it for granted. You press the button for air conditioning in your car and cold air starts to flow out of the car's vents. It's easy, it's simple, and it's a major convenience. Could you imagine driving to a meeting on a hot day and your car didn't have air conditioning? By the time you got to your meeting, you'd be a sweaty, stinky mess.
Have you ever wondered how the air conditioning in your vehicle works? If you're like most people, you probably haven't. But we're here to educate you painlessly. Air conditioning is the process by which air is cooled and dehumidified. The air conditioning in your car, your home and your office all work the same way. Even your refrigerator is, in effect, an air conditioner. While there are many physical principles that relate to air conditioning, this article sticks to the basics. It explains the general concepts of automotive air conditioning, the components used and what you need to know to keep your car's A/C system working properly.
Did you know that when you turn on the A/C in your car, you are burning extra fuel to make yourself feel cooler? It's weird to think that by burning something you become cooler, but it's true.
Do you remember anything from your high school physics class? Basically, air conditioning systems operate on the principles of evaporation and condensation.
Here's a simple example of evaporation. Imagine that you're swimming around in your backyard pool on a summer day. As soon as you get out, you start to feel cooler. Why? The water on your body starts to evaporate and turns into water vapour. And as it evaporates, it draws heat away from your body, and you get goose bumps. Now let's say you have a big glass of ice-cold Coke. You take a sip and set it down on a table. After a minute or two, you notice that water has collected on the outside of the glass. This is condensation. The air surrounding the glass becomes cooler when it encounters the cold glass, and the water vapour the air is carrying condenses into water.
Both of these examples occur at normal atmospheric pressure. But higher pressures can also change a vapour (or a gas) into a liquid. For example, if you look at a typical butane cigarette lighter, you can see liquid inside it. But as soon as you push down on the button, butane gas comes out. Why? The butane is under high pressure inside the cigarette lighter. This high pressure causes the butane to take liquid form. As soon as the butane is released and it encounters normal atmospheric pressure, it turns back into a gas.
Ok, those are the basic ideas. But how do they apply to making your car's vents blow cool air? The principles of evaporation and condensation are utilized in your car's A/C system by a series of components that are connected by tubing and hoses. There are six basic components: the compressor, condenser, receiver-drier, thermostatic expansion valve, the evaporator and the life-blood of the A/C system, the refrigerant.
Refrigerant is a liquid capable of vaporizing or turning into a gas at a low temperature. In the past, R-12 refrigerant was used in cars. But this chlorofluorocarbon (CFC) is harmful to the earth's ozone layer. Consequently, all vehicles built after 1996 use R-134a, a more environmentally friendly refrigerant. Even although it does not affect the ozone layer as did R-12, it still contributes to the green-house effect. By 2017 this refrigerant will also be phased out and a even better type of refrigerant will be in use. (Probably R-1234yf which has similar properties to R-134a, but a very low green-house effect).
How does each aircon component work?
*See detail diagram below as you follow each step...
Step One: The compressor is the power unit of the A/C system. It is powered by a drive belt connected to the engine's crankshaft. When the A/C system is turned on, the compressor pumps out refrigerant vapour under high pressure and high heat to the condenser.
Step Two: The condenser is a device used to change the high-pressure refrigerant vapour to a liquid. It is mounted ahead of the engine's radiator, and it looks very similar to a radiator with its parallel tubing and tiny cooling fins. If you look through the grille of a car and see what you think is a radiator, it is most likely the condenser. As the car moves, air flowing through the condenser removes heat from the refrigerant, changing it to a liquid state. Most cars have an auxiliary fan to assist with this process.
Step Three: Refrigerant moves to the receiver-drier. Some vehicles will have an accumulator instead of a receiver drier. This is the storage tank for the liquid refrigerant. It also removes moisture from the refrigerant. Moisture in the system can freeze and then act similarly to cholesterol in the human blood stream, causing blockage.
Step Four: As the compressor continues to pressurise the system, liquid refrigerant under high pressure is circulated from the receiver-drier to the thermostatic expansion valve. The valve removes pressure from the liquid refrigerant so that it can expand and become refrigerant vapour in the evaporator.
Step Five: The evaporator is very similar to the condenser. It consists of tubes and fins and is usually mounted inside the passenger compartment. As the cold low-pressure refrigerant is released into the evaporator, it vaporises and absorbs heat from the air in the passenger compartment. As the heat is absorbed, cool air will be available for the occupants of the vehicle. A blower fan inside the passenger compartment helps to distribute the cooler air.
Step Six: The heat-laden, low-pressure refrigerant vapour is then drawn into the compressor to start another refrigeration cycle.
- As you can see, the process is pretty simple. Just about every vehicle's A/C system works this way, though certain vehicles might vary by the exact type of components they have.
The best thing about air conditioning is that all you have to do is press a button to make it work. Air conditioning systems are pretty reliable. On a modern and relatively new vehicle, it is rare to have problems. And if there are problems, they are pretty much one of two things: No cool air or insufficient cool air. As cars age, due to vibration and temperatures in the engine compartment, you get wear and tear and things can start going wrong. If you own an older car and its A/C system doesn't seem to be working properly, here are some general troubleshooting tips:
No Cool Air
- Loose or broken drive belt
- Inoperative compressor or slipping or faulty compressor clutch
- Defective expansion valve
- Clogged expansion valve, receiver-drier or liquid refrigerant line
- Blown fuse
- Faulty Pressure sensor
- No Gas in system due to leaking component: any of the parts listed above or one of the A/C lines, hoses or seals
Insufficient Cool Air
- Low refrigerant charge
- Loose drive belt
- Slipping compressor clutch
- Clogged condenser
- Clogged evaporator
- Slow leak in system
- Partially clogged pollen filter or expansion valve
- Most A/C repairs are best left to a qualified and approved repair shop or fitment centre. Recharging the refrigerant, in particular, requires special equipment that most people don't own. There are a couple things you can do, however. First, make sure to have the system checked regularly according to your vehicle's owner's manual. Second, if you live in a place with a cold climate, it might not make much sense to run the A/C during the winter months, but many shop technicians recommend running your A/C system regularly, because it contains a light mineral oil in the refrigerant to keep the compressor properly lubricated. The general rule of thumb is 10 minutes per month. A second advantage is using your aircon to demist or defog your windows when it is raining or very cold. This works because the air coming out of your vents is dry air therefore absorbing the moisture from your windows, thereby clearing them.
So those are the basics behind air conditioning. The next time you're riding along in a car and you hit the A/C button, you can be thankful for R-134a!
DO THE JOB RIGHT, THE FIRST TIME!!!
Things fitment centre's, auto electricians, workshops or anyone who does aircon repair needs to know from our aircon experts.
FLUSH AND VACUUM
- The compressor failed for a reason. There are two main reasons why compressors fail. Number 2 is oil starvation, where the system is not properly lubricated and thus burns out. The number 1 reason is contamination in the system. Cleaning out this contamination is crucial to ensuring that the new compressor is not also contaminated. We require every system to be properly flushed and vacuumed.
We recommend flushing the system, then inspecting what comes out through a filter for discoloration or metal flakes. Always flush and evacuate before replacing a compressor. Always use A/C system flush solvent appropriate for the vehicle's system. If it is not perfectly clean after the flush and vacuum, we recommend re-flushing the system. If it is still not perfect, then we recommend replacing the evaporator and possibly other parts such as hoses and pipes.
- Most newer vehicles have serpentine or parallel flow condensers that simply cannot be cleaned and must always be replaced. The same applies to the drier / accumulator and orifice tube / expansion valve or block valve.
- Oil is crucial to a properly functioning A/C system. It is crucial to use a high quality oil to ensure that it will not break down over time. Remember the number 2 cause of compressor failure is oil starvation, often from the oil decomposing over time. That decomposed oil can often be the cause of the debris in a contaminated system. We recommend a double end capped PAG oil or better. Check the book for the proper viscosity. Oil comes as 46, 100 or 150 viscosity. You will need the correct type for your vehicle; they are not interchangeable and higher is not better. Each compressor is designed to work with certain oil.
Many of our new and remanufactured compressors come pre-filled with oil. We can never guarantee that the oil is the correct amount. Most manufacturers put just a few millilitres of oil in for testing and shipping. We can also never guarantee the quality of that oil, or how long the oil has been in there. Oil exposed to atmosphere can expedite the breakdown process. Therefore, we recommend dumping all oil and starting with a sealed bottle of premium oil. Do your own measuring to ensure the job is done properly. Also check the specifications book; many manufactures want half oil in the compressor and half in the drier, some want all in the compressor. Don’t guess, follow the instructions.
- Pure R134 for R134 systems and retrofits. Pure R12 for R12 systems. No exceptions. There are lot of Refrigerant alternatives out there. And many of them are dangerous blends which are detrimental to your vehicle's aircon system. The bottom line is that none of those have been tested to work with the seals and gaskets inside our compressors. We can therefore not warranty our parts when you use these products. Ensure that you are only using refrigerant from a sealed, trustworthy source that are able to supply a valid verification certificate of the contents of their refrigerant. Be careful, there are many of fraudulent products on the market!
- The drier is the filter on the A/C system. Some vehicles have an accumulator and some have a receiver drier, but either way the internals do the same thing. A new drier is required every time you change the compressor, no exceptions. Inside a drier is a desiccant element that pulls moisture and debris from the system. Remember that moisture from water is very bad, it alters the viscosity and can ruin a system.
Just like you wouldn’t change your engine oil without changing your oil filter, the same is true on A/C systems. You want that drier cleaning your system to ensure long lasting performance. You definitely do not want that old drier dumping debris back into the system.
- Most modern A/C systems use O-Rings at every connection. Half of all A/C leaks turn out to be wrong, bad or improperly installed O-Rings. We recommend that O-rings be changed with the compressor. We recommend that as you remove an O-ring, that you tape it to a piece of paper and note next to it where it came from. This way if you have a problem in that area later, you can double check that you used the correct O-ring.
- The expansion device is a generic term. It can be an orifice tube, expansion valve or expansion block. An orifice tube should always be replaced, it should never be cleaned. An expansion valve or block is a little more difficult. They should always be removed and inspected or replaced during a repair. A stuck expansion device can allow too much pressure to build in a system and thus blow out the head of the compressor.
The rule of thumb is that if you are replacing the compressor because it is leaking or not blowing cold enough, then cleaning the expansion device may be acceptable. Any other failure requires a new expansion device. If unsure, rather always change the expansion device.
- We carry the same warranty on compressors and parts as our manufacturer / suppliers which is normally one year. Remanufactured compressors normally also carry a one year warranty. (Above Conditions apply). While our warranty gets into detail, the important thing to understand about it is that it is crucial to do the job properly. Trying to cut corners will result in a system failure. Even if you think it is “just the clutch,” there is no excuse for not doing the job correctly the first time.
The first thing we will ask if you have a problem is to prove all the above procedures were done correctly. We require this, because we know that if you do the job properly, you will probably have no problems at all.