Cool Cat Boogey… How Your Air Conditioning System Works

If you are old enough to remember long summer car trips without air conditioning..sweaty thighs on vinyl upholstery…siblings crawling all over you to get some relief from the heat…your dad, or mom threatening "to pull this car over if you don't stop arguing"…yuck!  you can truly appreciate today's auto air conditioning systems. 

Have you ever wondered how your air conditioning works? Why would you? Press a button and cool air rolls out of your vents. If you're like most people, you probably haven't wondered where that cool air comes from …until it's stopped working. This article explains the basics of how air conditioning works, what the components are called, and how to best maintain your system.  

Air conditioning is the process by which heat is removed from air and air is dehumidified. Basically, air conditioning systems operate on the principles of evaporation and condensation.

Evaporation!

Here's a simple example of evaporation: Imagine that you're pedaling your bike down the road on a hot, summer day. If you throw some water from your water bottle on the front of your jersey, your chest will suddenly feel much cooler. Why? The water on your jersey (and chest)  starts to evaporate and turns into water vapor. And as it evaporates, it draws heat away from your body.  

Condensation!

Now let's say your neighbor hands you a ice-cold beer. (Your neighbors are nicer than mine) 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 bottle. This is condensation. The air surrounding the bottle becomes cooler when it encounters the cold bottle, and the water vapor in the air condenses into water.

Parts!

Evaporation and condensation are created in your car's A/C system by parts that are connected by tubing and hoses. There are six basic parts to your AC system: the refrigerant, the compressor, condenser, receiver-drier, expansion valve, and the evaporator. A description of these parts and how they work together is as follows:

The Refrigerant

Refrigerant is a liquid capable of vaporizing (turning from liquid to gas) at a low temperature. It used to be that chlorofluorocarbon (CFC) R-12 refrigerant was used in cars. But R-12 harms to the earth's ozone layer. Because of this, all vehicles built after 1996 use R-134A, a more environmentally friendly refrigerant.

The Compressor

The compressor is driven by a belt connected to your engine. When you turn your air conditioning on, the compressor pumps refrigerant gas to the condenser under high pressure.

The Condenser

The condenser looks like a small radiator, and it is typically is located in front of your car's radiator. If you look through the grille of a car and see what you think is a radiator, it is most likely the condenser. The compressor moves refrigerant to the condenser as hot gas. As the car moves, air flowing through the condenser removes heat from the refrigerant, changing it to a liquid.

The Receiver Dryer

The liquid refrigerant moves from the condenser to the receiver-drier. The receiver-dryer functions as a storage tank for the liquid refrigerant and it is designed to remove moisture from the refrigerant, so that the moisture doesn't freeze up and block the air conditioning lines.

The Expansion Valve

As the compressor continues to push refrigerant through the system, liquid refrigerant under high pressure moves from the receiver-drier to the expansion valve. The valve removes pressure from the liquid refrigerant so that it can expand and become refrigerant vapor in the evaporator.

The Evaporator

The evaporator, like the condenser, looks like a radiator. It is usually located behind your dashboard. It consists of tubes and fins and is usually mounted inside the passenger compartment. As the cold low-pressure refrigerant rushes into the evaporator, it vaporizes 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.

Recirculation

After leaving the evaporator, the hot, low-pressure refrigerant, in the form of gas, not liquid,  is then drawn into the compressor to start another refrigeration cycle.

Troubles and Their Causes

When we have customers complain about their air-conditioning systems, we usually first ask: "Do you have no cool air, or do you have too little cool air?" The answer to that question indicates what sort of components are affected.

No Cool Air

The following malfunctions can cause your air conditioning system to fail to produce any cool air:  

• Inoperative compressor or slipping compressor clutch (the compressor is "seized up" or the clutch, which engages the compressor when the system is turned on is broken). The fix for this is to repair or replace the compressor.
• Loose or broken drive belt (the belt that turns the pulley on the AC compressor so that it will run is either too loose to turn the pulley, or is broken). The fix for this is to replace a broken belt or tighten a slipping belt.
• Defective expansion valve. Replacement of the expansion valve is called for.
• Blown fuse. Replacing the blown fuse is the fix here.
• Clogged expansion valve, receiver-drier or liquid refrigerant line. Finding the clog and removing it are the fix here. Leaking component. Replacing the leaking part and recharging the system is the fix for this problem.

Not Enough Cool Air

The following malfunctions can cause your air conditioning system to fail to produce enough cool air: 

• Loose drive belt. If the drive belt is loose, the compressor will turn slower than if it is tightened correctly. The fix is to tighten the belt.
• Slipping compressor clutch. Repair of the clutch or compressor will fix this problem.
• Low refrigerant charge. Over time, the system will lose some refrigerant. Recharging the system will fix this situation. We always check for leaks before doing this.
• Clogged condenser. Replacing the condenser will fix this problem.
• Partially clogged filter or expansion valve. Replacement of these parts is the most common solution to this problem.
• Clogged evaporator, Replacing the evaporator is the solution to this problem.
• Slow leak in system. Finding the leak, which is sometimes difficult, depending upon the size and location of the leak, and repairing it, are the answer here. We add dye to the system that is visible under a "black light", to help us find leaks.

Can I Fix My Air Conditioning by Myself?

Unfortunately, unless you have access to the proper equipment, most air conditioning repairs should be done by a competent repair shop. For example, recharging the refrigerant requires a charging system that is an expensive piece of machinery.

O.K.  I Understand Repair is a Job for Professionals, But How Can I Maintain My Cool?

·      Run your air conditioning 15 minutes a month, even during the winter, to lubricate your compressor. Refrigerant contains a lubricant, and running the system distributes that lubricant throughout the system and through the compressor, which will help avoid problems with your compressor. As the compressor is the most expensive part of any system, this is well worth the trouble. In the winter, it's o.k. to run your air conditioning and heater at the same time, and the air conditioner will help defrost your windshield much quicker than using your heater alone.

·      Have the system checked annually for leaks or other problems.

·      Don't ignore noises coming from your compressor, pulleys or belts.  

So now you know how to maintain your chill. See you down the road!