Air Conditioner A-Z
First…......let's do some reading (BTW, these quotes aren't all mine):
Air Conditioner: How does it work?
http://www.explorerforum.com/forums/showthread.php?t=160498
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A clarification regarding how our air conditioners work.
The orifice has a hole in it. There is liquid on one side and pressure forces the liquid through this tiny hole which vaporizes it, something like a sprayer on the end of a garden hose.
When liquid is changed to a vapor like this a miracle occurs, it absorbs heat. This is why the evaporator follows the orifice, blowing cabin air through the evaporator transfers the heat to the expanding vapor inside the evaporator. Out of the top of the evaporator is low pressure gas.
The low pressure gas, and any suspended liquid refrigerant, goes to the accumulator, where any remaining liquid falls to the bottom leaving only low pressure gas. This is where the LP port is.
This low pressure gas is compressed by the compressor into ..... hot high pressure gas. Through the muffler and to the condenser. Just before the condenser is the high pressure port. At the condenser another miracle occurs, blowing air through the condenser removes the heat from the hot HP gas and turns it into a liquid. This is the liquid at the orifice that started this. So the orifice is the device that provides a difference between liquid and vapor.
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Then, What are the common problems?
What's wrong with my Air Conditioning?
A number of things can happen to make your A/C quit working. Here, we'll go over some of the common problems, and what you can do to fix it.
Leaks / Low Refrigerant
No A/C system is completely, 100% sealed. Over the years, small refrigerant particles will leak out, up to 1/2 ounce per year. On smaller-capacity systems, this will become noticeable a lot quicker than a larger capacity system. In this case, the most practical thing to do is simply add a bit more refrigerant. You will want to hook up a set of manifold gauges to make sure that the system has at least some pressure in it before you add refrigerant, because if the system is completely empty, you might have a most severe leak. At best, you will still have AIR in the system, and you want NO air in there.
Symptoms of low refrigerant include rapid cycling of the compressor clutch, or clutch will not engage, little or no cooling, very oily spots on A/C components.
A severe leak will require repair or component replacement. To find a leak, there must be some refrigerant in the system. An electronic 'sniffer' or dye are the most effective ways of finding a leak. Most A/C shops can perform this service for a minimal charge. Some retail auto parts stores also loan or rent tools for this.
Once the leak is identified, the component should be repaired or replaced, and the system serviced.
*Tip* - Evaporator leaks can be difficult to find, since the evaporator is usually not easily accessible, located in the dash of the vehicle. With dye in the system, place a white, preferably unused baby diaper under the evaporator drain tube. Moisture will drip on to the diaper. If there is dye in there, you'll know it!
Poor Airflow
One of the most-missed problems is poor airflow. Your A/C comes on, but it's not very cold. If you have a gauge, the high side pressure seems awfully high.
There are a couple of quick, easy things to check. First, make sure the condenser is debris-free, and that the fins are not all bent over. The condenser is located right in front of the radiator. Bugs, rocks, plastics bags, etc. covering the front of it prevent air from passing through, cooling not only your radiator, but also the refrigerant in the condenser.
All engines have either a fan clutch or radiator / condenser cooling fans. Fan clutch go out all the time. The fan clutch is located between the radiator and the engine, and has a big fan blade attached to it. With the engine on, that fan should be turning very fast, and moving a lot of air, TOWARDS the engine. Running correctly, you will not want to get your fingers near it. I recently repaired a 1996 Chevy truck that had blown the compressor shaft seal. While diagnosing the system, I noticed that the fan was barely turning. I could actually stop it with my hand. (not recommended for the non-professional) Because there was poor airflow, the pressure (pressure is temperature) built up from the condenser to the compressor, and was more than the compressor shaft seal could handle.
If the vehicle has an electric fan, make sure it (or they) comes on, and that the air is fast, and moving TOWARDS the engine. If the fan(s) does not come on, check the fuse. If that's not it, you may need to replace the fan.
*Tip* - You can confirm proper airflow by TEMPERATURE TESTING. A good thermometer that can be touched to the inlet and outlet of the condenser will confirm proper airflow. You should see a 20 to 40 degree drop from the inlet to the outlet of the 2 condenser pipes. For example, if you measure the temperature at the inlet (where it comes from the compressor) and have a temperature of 160 degrees, the outlet should be 100-140 degrees. Less than 20 degrees difference usually indicates poor airflow. MORE than 40 degrees usually indicates a restriction in the condenser.
Restrictions
A restriction is a condition where some piece of debris has lodged in a component, and is 'restricting' the flow of refrigerant. Condenser restrictions are the most common. Most late-model condensers have very small passages, as low as 6mms! When there is a restriction in the system, the flow of refrigerant is greatly slowed, or sometimes stopped completely. The blockage causes pressure to build up behind the restriction, and will cause damage to the components behind it.
The most effective way to locate a restriction is with temperature testing. With a good thermometer, temperature (which is pressure!) can be measured ANYWHERE on the system. Large drops in temperature can be identified and repaired. For example, a restricted condenser...If the inlet measures 160 degrees (about 295 psi) and the outlet measures 90 degrees (about 103 psi), it means the refrigerant is slowly leaking past a restriction. Because the refrigerant spends more time in the condenser, it has time to cool of more. Problem is, that 295 psi will continue to build back, and will eventually blow a seal somewhere, probably in the compressor.
Some restrictions can be repaired by flushing the restricted component, but parallel-flow condensers usually need to be replaced.
Improper Refrigerant Charge
As A/C systems become smaller and smaller, the amount of refrigerant in the system becomes critical. The correct charge for an A/C system has been calculated and engineered by vehicle manufacturers for optimum performance. Here are some tips to keep in mind when charging a system:
Charging with cans: A 12 ounce can of refrigerant gives you 12 ounces of refrigerant, right? Well, not always. If you are using a gauge set to charge, those hoses can hold up to 4 ounces of refrigerant themselves. On a 56 ounce capacity system, those 4 ounces might not make a big difference, but on a 1 pound system, you can bet it will. Also, notice how when you pull the can tap off, how the can wasn't quite empty? Yep, another ounce or 2 there.
Too much! Your A/C isn't quite cooling, so you run down to the parts store or a big box retail store, and buy a recharge kit. We in the industry call 'em suicide kits. You add a can of refrigerant. Well, with A/C, too much isn't better.
Retrofitting: Vehicles manufactured prior to 1993 and some 1994 originally came with R12 refrigerant. Because of the cost of that refrigerant, most folks opt to retrofit to R134a refrigerant. Problem is, there is no set standard for how much R134a refrigerant to use in an R12 system. There are many misconceptions about how much to use, and some people have come up with percentages of original charge. I've heard to use as little as 60% of the original charge!
So how do I know if I have the proper charge? Our old friend temperature testing can help determine if you have the proper charge. Orifice tube systems are the easiest and most accurately confirmed systems. It can be done on expansion valve systems, but you'll need to get on the evaporator side of the expansion valve.
Here's how: Measure the evaporator inlet pipe and record your temperature. Now measure the outlet pipe of the evaporator. Those 2 temperatures should be as close to equal as possible, at least within 5 degrees of each other. If the outlet is MORE than 5 degrees warmer than the inlet, you still need more refrigerant. If the outlet is MORE than 5 degrees cooler than the inlet, you have too much refrigerant in there.
Final tip: If your A/C is working, don't mess with. If you have an R12 system, you do NOT need to have it converted to R134a just because someone tells you that R12 is gone. If it's working, leave it alone.
If your system is working and sealed, you DO NOT need to replace your filter drier or accumulator. This is not a part that wears out. The only time you need to replace it is when the system is opened, or if you've had a leak that allows air (and moisture) into the system. If someone tells you you need to replace it every 3, 5 or 7 years, they're trying to sell you something.
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From:
http://reviews.ebay.com/A-C-Diagnosing_W0QQugidZ10000000000946036
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Aloha, Mark
