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AUTOMOTIVE AIR CONDITIONING
TROUBLE SHOOTING GUIDE
Charging your automotive AC system is critical to the successful completion of your AC repair job. The first step is to look up the correct charge by weight and to determine the type and quantity of oil required. When in doubt refer to the manufacturers specifications.
There are three types of oil used in todays' automotive air conditioning systems. Mineral oil, PAG oil and Ester oil.
Mineral, or petroleum based oils are used in the older systems that use R12 refrigerant. They are not compatible with the R134a refrigerant in use today.
PAG oil, or Polyalkylene Glycol, is the oil most often used by manufacturers at the factory. If you have NOT flushed your system and are just adding oil you will want to use the same type of oil that is in the system if at all possible. We do not recommend mixing different types of oil.
Ester oil, or Polyoil Ester, often referred to as POE , is our favored oil for retrofits. It is compatible with both R12 and with R134a so if you are not satisfied with the result of your retrofit you can simply remove the R134a and recharge with the more expensive R12.
Remember that most synthetic refrigeration oils are hygroscopic in nature (absorb water) and therefore should not be unnecessarily exposed to moisture and humidity. Introduce the oil into the system when you are ready to vacuum and charge it, not a week before. Keep the container sealed.
First you must vacuum your system. This removes any air and moisture which may be in your system. Do not be tempted to skip this step, especially if you intend to keep the vehicle. Over time, gasses (freon) will combine with moisture and create acids in your system. This will eventually cause component leaks, especially in your evaporator. You will pay the price for taking this shortcut a year or so down the road.
Take your manifold gauge set and connect the center hose (usually the yellow one) to your vacuum pump. Connect the blue hose / gauge combination to the low pressure side of the system. That would be the suction side of the system and is the hose which connects the suction port of the compressor to the accumulator or the evaporator. Trace the hose to be sure! Low side service ports can be on the hose fittings, the accumulator body, the evaporator pipe or the compressor. This step is very important. If you are not certain which is the low side port STOP RIGHT NOW!!!! Bring it to a professional. Connecting to the wrong port can cause the freon container to violently explode, causing SERIOUS INJURY OR DEATH. By connecting to the wrong port you will be pumping into the container instead of emptying it and cause it to rupture due to over pressurization.
Next, connect the red hose / gauge combination to the high pressure side of the system. The high side service port(s) may be located on the compressor, in the discharge hose fittings (compressor to condenser) or in the liquid line fittings (condenser to expansion valve). On older R12 systems the high side service ports may be the same size thread OR a smaller thread than the low side ports. If it is a smaller thread you will need an adapter to attach the gauge hose. On the newer R134a systems the service ports are not threaded and different sized QUICK DISCONNECTS are used to make the connections.
You are now ready to begin. Turn on the vacuum pump and open the low side gauge set valve. The needle should be moving towards vacuum. Let the pump run for 30 minutes or so, longer if the system has been open and exposed to high humidity for a long time. The gauge needle should be at the maximum position (~29-30" Hg). If the gauge does not draw down, you have a leak. Check your connections.
When you are satisfied you have drawn a vacuum for a long enough time close the gauge set and turn off the vacuum pump, in that sequence. When you first shut the gauge valve the low side needle will typically lose an inch or two of vacuum and then remain steady. It should remain steady indefinitely. If the needle moves you have a leak and will need to find it before you go any further. It is a good practice to let the vacuum hold for a while, thereby using it as a leak test before charging the system.
Once the system is vacuumed and you are satisfied you have no leaks, you can begin charging. Use the 12 oz. cans rather than the large 15 or 30 lb. containers if you do not have a charging station, thus minimizing the possibility of overcharging. Add the weight of the individual cans (usually 12 oz.) and use a postal scale to determine how much you have removed from the last can. Charge only with "gas" (can upright) and NOT with "liquid" (can inverted). Never "slug" your compressor or charge with liquid as it will destroy your compressor.
To facilitate the flow of the gas from the can to the cars AC system you can employ several methods. Since the system is in vacuum, most of the first can should go in on its own. After that, you can submerge the can in a pot of warm, NOT hot, water. This will raise the pressure of the gas in the can. A gas will always move from an area of high pressure to an area of low pressure. The warm water will cause the can pressure to rise and the freon will flow into area of lower pressure, namely the AC system.
HOT BOILING WATER CAN CAUSE THE CAN TO BURST CAUSING SERIOUS INJURY OR DEATH.
Once the gas flow has become impractically slow you can start the engine and turn on the system, as long as you have been able to put in enough freon to permit the oil to circulate. Generally, one can is enough to accomplish this but every system is different. You will need to pay close attention to your compressor to be sure it does not overheat. Place your hand on the body of the compressor to monitor the heat. A good rule of thumb is that the compressor should be cool enough to touch and leave your hand on for no more than a few seconds. If you are not sure, turn off the compressor and wait until it cools and start over again. Take note that if the system pressure is too low,(>28 psig or so), it may be necessary to jump or bypass a low pressure or cycling switch in order to get the compressor to turn on. You may also accomplish this by disconnecting the compressor from the harness and connecting it directly to the battery with alligator clips.
When it is time to put in the last can, place it on a postal scale to monitor the weight as it empties. Use that to determine the exact charge.
Be sure to take great care when charging the system. The chance for personal injury is great. Use adequate safety goggles and be absolutely certain you are charging on the low side. We cannot over emphasize the importance of this.
A CAN OF FREON WILL EXPLODE IF ACCIDENTALLY CONNECTED TO THE HIGH SIDE OF A RUNNING SYSTEM BECAUSE YOU WILL BE PUMPING FREON INTO THE CAN INSTEAD OF EMPTYING IT. THIS WILL CAUSE IT TO RUPTURE AND VIOLENTLY EXPLODE. DO NOT GUESS. IF YOU ARE NOT SURE BRING IT TO A PROFESSIONAL!!!
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