Car ac
How car ac systems should be recharged. Before recharging auto air conditioning systems it is highly recommended to remove any air and moisture from the system before you add a Freon charge. Pulling a vacuum on the system does this. If you decide to skip this step, your air conditioning may work after recharging, but the question is for how long.
Air in the system restricts the refrigerants ability to change its state from a gas to liquid and can cause pressure problems and lower the cooling efficiency of the car ac. Moisture on the other hand can cause freeze ups, and also restrict the refrigerant flow. Moisture can also form an acid when mixed with refrigerant. This will cause corrosion inside the system. A ac vacuum pump connected to a manifold ac gauge set will remove all of this air and moisture from an empty system. You must recover the remaining Freon from the car air conditioning system before you pull a vacuum. More details about why and how auto aircontioning works are available from the article links below. But for now lets move onto the problems and procedures with auto ac recharging. Car ac rechargingWhen the system is operating refrigerant is only charged on the low side service port. If you connect a small can of Freon to the high side with the system on, the Can may explode from the high pressure introduced into it. But certainly no Freon will flow from the small can into the high side with the compressor operating. The importance of the correct amount of Freon added during the charging procedure is extremely important. The efficient operation of the air-conditioning system depends greatly on the correct amount of refrigerant installed in the system. The system capacity is usually marked on an engine compartment sticker.
A low charge will result in poor cooling under high heat loads due to a lack of reserve refrigerant. This can cause the clutch cycling switch of the compressor to click on and off. This cycling of the compressor clutch is also a telltale sign that your system is low on refrigerant. But you should always connect your manifold gauges to verify this low-pressure condition. An overcharge of the AC system can also cause inadequate cooling. This is because a high liquid refrigerant level in the condenser decreases efficiency. If the system is overcharged compressor damage can also occur when and if liquid Refrigerant enters the compressor. Once again an ac gauge set connected to your high and low side will show this. If too much Freon is in the system, you will have high-pressure readings on both sides. Car AC diagnosis
The normal pressure readings on a vehicle's air-conditioning system will vary with the outside temperature. But a good rule of thumb is to have between 30 and 45 PSI on the low side. And a reading of 125 psi to 200 psi on the high side. Again, this will vary with the amount of charge in the system and with the outside temperature. If you should connect your manifold gauges, and see readings that are out of this range then your air-conditioning system is probably not cooling effectively. Online car repair manuals can provide you with diagnostic steps and repair procedures if these hi or low side pressure readings are out of range.
The reason for this is as follows. The condenser fan removes heat from the high side of Freon. If this fan is not blowing across the condenser, the refrigerant will have extremely high temperatures and as we learned before, the higher the temperature, the higher the pressure. This is why I recommend fully understanding how a car air-conditioning system works before attempting diagnosis and repair. Even if you are taking your vehicle in for a/c service it is still worth learning about. This next link will take you to a good place to start. Go from
car ac to automotive air conditioning
 Custom Search If your car ac system still has the old R12 freon in it this next link will show you how to retrofit auto air conditioning Car ac systems are dangerous to work on. When in doubt leave it for the professionals. If you are going to perform diy auto ac repairs please review this next page for ac safety tips Learn more about what is covered on this car repair website on the homepage. Also learn more about the mechanic that built it and provides auto repair information
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Just as an example, if your high side pressure is over 200 lets say even over 250. This is an indication of a problem. Often when I see this reading, I will first look at the condenser fan operation. 
