Air Conditioning Compressor Basics
469,180
Published 2019-02-20
Compressors come in all sorts of types, including reciprocating, scroll, rotary, screw, and centrifugal compressors. All types increase the pressure of vapor refrigerant; they all decrease the volume to increase the pressure, which causes it to move.
Many compressors are powered by electrical plugs (often made of Fusite), which connect to the motor on the inside. Compressors generally have three different designs for varying degrees of accessibility: hermetic (sealed), semi-hermetic (bolted), and open-drive (where the compressor is separate from the motor).
Compressors can only compress vapor, not liquid. We check the superheat to make sure we're only sending fully vapor refrigerant to the compressor; sending liquid to the compressor can damage it. The suction gas temperature is also important to ensure that the compressor head is being cooled adequately (for refrigerant-cooled compressors) and to make sure the mass flow rate is good.
Mass flow rate also plays into compression ratio, which is the ratio of absolute discharge pressure to absolute suction pressure. The compression ratio is a measure of how efficiently a compressor is pumping; too much compression indicates a lack of efficiency (such as through re-expansion).
Compressors have oil inside their crankcase, and a small amount of oil circulates with the refrigerant. Oil control is very important, as compressors have bearings that need to stay lubricated. If liquid refrigerant gets into the compressor, it can cause foaming and oil loss, which can lead to increased mechanical wear and possible premature failure over time. When liquid refrigerant migrates to the crankcase during the off cycle, it can create a flooded start that causes a lot of oil loss. (Crankcase heaters, liquid line solenoid valves, and hard shutoff TXVs can all help prevent flooded starts.) Overheating can also cause the oil to break down.
When the compressor increases the refrigerant pressure, it also increases the refrigerant pressure because the molecules move more quickly in a smaller space. For the most part, the heat content stays the same (with the exception of some minor contributions, such as from the motor windings) despite the temperature increase.
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All Comments (21)
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Excellent. Many people don't realize that compressors are cooled by the proper refrigerant charge, using that coolant on the return or suction line, to keep the compressor from overheating. Thus destroying the oil and parts within the hermetic or semi-hermetic compressor. Very well explained. Thank you for all of your superb videos.
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You teach very well. The way of your teaching reminds me when I was in technical schools in Germany . You are true professionl.
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I have been in Germany. The style of your teaching reminds German colleges . Great job , You are true professional. Please continue 👍
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the video is factually correct with good usage of technical terms that most technician would have a problem with. Plus, a good explanation of why the temperature of the vapor refrigerant is increased was made. Some people would mistake increasing pressure means increasing the temperature but in fact the superheated complete vapor does not correspond to pressure/temperature relationship.
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Wow! So glad I found your channel this is so awesome!! I work in residential construction, not in the HVAC trade but lately have wanted to understand more about it, mostly because I wanted to install some ductless heat pumps, but I'm falling down a rabbit hole and it's great! Thanks for the education it is definitely improving me! So again thanks for that!
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Simplified and easy to follow. Good video!
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i still have a troubleshooting card on compressors from way back in school there are so so so many possible reasons for failure of a compressor your have to be a genius to remember them all , !
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Nice work on all your videos. You folks do a great service to our excellent industry. Thank you.
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Great video! I'm in school right now and every little bit of knowledge helps!
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I love how you explain step by step 👏🏾, very knowledgeable , big help thanks
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Fantastic snapshot into the world of refridgeration. Definite subscribe.
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Trying to get my universal refrigerant license and this helped a ton. Thank you!
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I like the way u put things out ! simple , clear and plain. Thx u sir .
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Remember: a compressor cannot compress liquid
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Very insightful! Very clear explanation of principle of VC Cycle without using any diagram!
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I did not have much science in high school but years later I have had the oppertunity to gain insights of physics of fluids and their properties of change from one state to another . Brian you must have had alot of school science to grasp and understand the laws of physics . You do a great job of presentation in this video , and not lecture over our heads of your topic on compressors . I gather more and more information and evolving skill each time I watch your videos Cheers
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I wish i had these videos when I studied. Great work!
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Really well-explained video of the process. Not in the industry but I found it quite fascinating. Thank you.
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Masterful just masterfully said,thank you!
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Very easily and nicely explained . Thank you
