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Car and Truck Air Conditioning Advice

Auto Repair and Maintenance Advice: Air Conditioning Overview

How It Works:

While it may seem the car air conditioning system is creating cold air, it actually works by removing heat. The car a/c system contains a substance called refrigerant that can easily transfer from gas to liquid and back and absorb heat at a low boiling point. Cars built prior to 1994 mostly used the refrigerant R-12, trade name Freon, but due to its contribution to ozone depletion, newer cars mostly use R-134a, an environmentally safer substance. Things get started in the a/c system’s compressor on the high-pressure half of the system. The compressor, powered by an engine drive belt, acts as a pump drawing refrigerant from the low pressure side and compressing it until the gas becomes heated. The high pressured, hot gas is discharged from the compressor into the condenser, which is similar to the car’s radiator and located just in front of it. Here the refrigerant dissipates heat as it travels through the condenser’s coils, surrounded by a coiling core, and ends as a high-pressured liquid. Cool air coming from the grill and fans play a crucial role in cooling the refrigerant. Proper airflow is crucial.

At this point, there are two possible variances depending on whether your car uses a receiver-drier or an accumulator (never both), consult your manual to see which you have. The receiver-drier separates any gaseous refrigerant from the liquid and stores it when cooling needs are low. The drier also contains a filter to remove debris and chemically removes moisture with the highly absorbent silica, preventing damage to the system by frozen water particles and corrosion. Next, the refrigerant travels to the thermal expansion valve (TXV), which regulates, or meters, the flow of refrigerant as it goes into the evaporator, using a bulb sensor to determine how much refrigerant to release, based on temperature. The TXV is ultimately what allows you to control the airflow and temperature when using the ac. Once the refrigerant exits the TXV it is on now the low-pressure half of the system in the evaporator, which causes the refrigerant to expand and vaporize. The evaporator is similar is a series of coils with fins. The refrigerant absorbs heat from the warm air passing through the fins. As a result cool air is left. Moisture in the warm outside air condenses to liquid on the cool evaporator coils, helping control humidity. There is a fan behind the evaporator that blows the cool air into the car. By the time the refrigerant has passed through the evaporator, it is entirely in vapor form and ready to be pulled back into the compressor to start the cycle again.

If your car does not use a receiver-drier and expansion valve it will have an accumulator and orifice tube. The orifice tube will be located between the condenser and evaporator, although exactly where may vary, and controls the flow of refrigerant into the evaporator. Unlike with the expansion valve, the flow is always at a constant rate. The cycling of the compressor instead controls the air temperature and flow. The tube also contains a filter to catch debris. The refrigerant flows into the evaporator in liquid form and acts similarly to the other system. The only difference is that at the evaporator outlet is the accumulator, which functions like a receiver-drier to separate liquid refrigerant from gaseous before returning to the compressor. Desiccant is also used to absorb any harmful moisture.

Potential Problems

Unfortunately, in car air conditioning systems, a problem can have any number of causes, ranging from moderate cost to expensive. Unless you really know what you are doing, it is best to take your air conditioning problem to a mechanic. Pinpointing a problem can be difficult, and great care needs to taken with refrigerant. Releasing it from the system, even by accident, is illegal. To find a mechanic you can trust, click here to locate a pre-screened auto repair and maintenance expert.

• The most common automotive air conditioning problem is lack of cool air. Over time, all cars lose refrigerant. If cool air is insufficient, the car might just need an air conditioner recharge. Learn more about a/c recharge.
• Lack of refrigerant may also indicate a leak in the system, something your mechanic can find by running dye through the system or with special equipment designed to detect gas leaks.
• Insufficient cool air may also mean an expensive compressor problem, in the ballpark of $1,000 to replace at the average mechanic’s auto repair shop.
• A system blockage may also be the culprit. It is not uncommon for the screens in the receiver-drier or orifice tube to become clogged. Flushing the system and replacing drier or orifice tube should take care of the problem. Keep in mind that anytime the a/c system is open, the receiver-drier and accumulator must be replaced even if not previously damaged as they become saturated.
• If the problem is intermittent cooling, the system might be freezing and the orifice tube or TXV is blocked. An electrical problem may also be to blame.
• Unusual noise and buzzing may indicate a compressor problem and should be checked right away to prevent expensive damage.
• A bad odor indicates mold in the system, which can be taken care of by running an antibacterial through the system.
These are just a sampling of problems. If you suspect a problem, going to a local mechanic is the best bet.

Tips for A/C Care

While it may seem like a lot of thing that can go wrong, there are a few things you can do to prevent problems:

• Have your vehicle air conditioning system checked regularly, at least every two years, just like any other in your car or truck. This action may minimize damage and expensive repairs by catching a problem early.
• Run your system year round. Even if you live in a cold climate, ten minutes a month ensures that the condenser stays lubricated, as refrigerant contains light oil.
• A minute or two before shutting the engine off, turn off you’re a/c and put the fans on high. This helps prevent condensation and dries the drier/accumulator, which can help prevent mildew from forming.
• If you will be idling for a while, turn the ac off, as the condenser may not be able to cool enough, making the compressor work too hard.
• Check your car or truck manual for recommended climate control temperature and try to stick with it. This ensures that parts are not overworked.

Air conditioning systems, especially in later model cars are built efficiently. So with some luck and care, you can hopefully avoid major problems. Good Luck as always from AutoRepairKey.com!

Comments

[…] meaning there is not enough refrigerant to absorb the heat from the car. Find out more about how car and truck air conditoning systems work.  Recharging the air conditioner is needed when the refrigerant is low, and means adding the right […]

What’s Automotive Air Conditioning Recharge and Will It Fix My A/C? | AutoRepairKey.com August 11th, 2011 at 2:05 am

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