2003 Sierra A/C problems

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  #1  
Old 07-27-10, 02:03 PM
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Location: Michigan
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2003 Sierra A/C problems

Hello, I have a problem with my trucks a/c right now. When I am just driving around town at low speeds (<35mph) my ac works beautifully. It gets cold quickly and stays cold. When I get on the highway, the a/c is still cold and stays cold, but every couple minutes I hear a very loud "psssssst" noise, kind of like a pressure release noise. It is very similar to the noise that comes off my air compressor in the garage if I pull the relief valve. Is this a bad thing to keep happening? Should I not run the a/c anymore until fixed? What are some steps to get it fixed?
 
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  #2  
Old 07-30-10, 05:17 AM
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Well, the wife wanted the a/c fixed before going away this weekend, I took it in to a local shop and he told me that the noise I was hearing was the clutch engaging. He said it was a little louder than usual due to the fact that the freon was a bit low. He filled the freon, put floro dye in (to find leak later, he said it would have been a very small leak), and said the clutch had been overheating and making more noise, but was still working fine and didn't recommend replacing anything at this point...seems like I got a fair shake from him...
 
  #3  
Old 08-27-10, 10:24 AM
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Yes, Indeed it wounds like what you are hearing is the a/c compressors clutch engaging. Freon gets cold as it is placed under pressure. The compressor clutch's job is to engage to pressurize the system til it is at its maximum pressure it can safely allow. Once there the clutch then dis-engages and the pressure begins to drop as the refrigerant is circulated through the system. when the pressure drops to a specified point at which the refrigerant is at the verge of gaining temperature, the compressor will then kick back on. It will continually cycle this way the entire time you have ac turned on. If your charge becomes low the compressor will be kicking on and off rapidly (about every 2-3 seconds) because there is just not a large enough valume of refrigerant to keep it pressurized for long. This will not usually cause the compressor to be any louder, although if you are losing refrigerant then you are also losing small amounts of the PAG Oil that is in the compressor for lubrication purposes. Alot of mechanics will charge you for repairs to system that are not even done or done unnecessarily. Best thing to do is that as long as ac is cold, dont add anything to it. There is a sensor that monitors the pressure in the system and if the system is low enough to cause damage to compressor, it will not allow the compressor to engage at all and you will get no cooling from the ac period. Also, to verify if this is the actual noise, the other way to get the compressor to engage is to turn on heat and set to defrost. whenever you have on defrost, the compressor engages same as if you were using ac.
 
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