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I'm watching this repair video that replaces the AC Compressor and I'm exploring how feasible it is to just replace the o-rings on the hose and compressor side of the AC Compressor's ports.

I'd like to know what would physically happen when you disconnect any of the AC hoses as installed on a vehicle's AC compressor.

I assume they're under pressure and would leak refrigerant and or oil immediately upon disconnection, but I'm curious would all the refrigerant leak out? Basically do these hose fittings have any other seal/valve-mechanism beyond the o-ring or is it just the o-ring? I'm thinking of something analogous to a manifold gauge set that has that fitting you have to slide back to fit over the low pressure and high pressure ports, or something like a Schrader valve with a core that gets depressed when you engage the hose to the compressor. Is there anything like that on the hoses themselves going to the compressor or not really?

unbolting AC hose from compressor

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  • Now that I have thought about the valve design possibility to AC hoses I realize that design wouldn't make sense for a circulating system even if there was a depressing/unlocking tab sort of design to keep the valve open when the hose is bolted down. That valve would just get in the way of the fluid and add resistance. Also if one had some sort of ball valve at the tips of the hoses there would be the risk of them closing unexpectedly and probably causing damage. Refrigerant just isn't precious enough to warrant designing a valve controlled closed system just for parts swapping.
    – jxramos
    Aug 24, 2023 at 0:21

2 Answers 2

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If you pop the hose or any of the connections, you lose most all (if not all) of the refrigerant. It is under significant pressure. Enough you cannot get things sealed back up before it's gone.

In order to do work properly on an AC system, you should have the refrigerant removed. Purposely venting it to atmosphere is actually illegal in most places. When you are done with your repairs, then you have the refrigerant replaced with new.

I'm not sure the gist of what you're trying to do, but I try to wrench by one saying, that is: If it ain't broke, don't fix it. What does that mean? If the something you are trying to fix works perfectly well in the first place, it doesn't make sense to try and fix it, because you are only wasting money. From the sounds of what you are talking about, you are thinking about changing out o-rings just for the sake of changing them out and not because there is any real issue with them. My suggestion is, if this is what you're thinking of doing, don't. It isn't worth it.

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  • My AC compressor looks like it's been leaking AC oil, it started small but the other day I found a good size puddle drip past the splash guard. This was a good exploration for looking into the feasibility of a cheap fix around the o-rings themselves rather than replacing the whole compressor both hopefully without needing to replace the all the refrigerant. But that doesn't sound like it's the case. Live and learn :D
    – jxramos
    Aug 23, 2023 at 20:55
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    @jxramos - The AC system is going to lose refrigerant before it will show leaking PAG oil. I'd double check to ensure you're looking at the right place for an oil leak. Aug 23, 2023 at 21:05
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    Also the safety factor that refrigerant under pressure could easily escape and get in your eyes, leading to possible blindness. In a contained area can effect the respiratory system. And to properly charge it special equipment and knowledge is required, without which could very likely cause expensive damage to the system.
    – Jupiter
    Aug 24, 2023 at 11:10
  • Just dug in tonight with an endoscope. It was not the AC compressor but coolant leaking out. It was green and slick and felt oily to me but the compressor checked out visually. The water pump is leaking it would seem.
    – jxramos
    Aug 26, 2023 at 5:50
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jxramos, did you watch that video from the beginning? In the first minute, the presenter warns viewers to remove refrigerant before any repairs, suggesting a local repair shop. Legally, refrigerant must be removed into reclamation canisters (15/30 lb capacity canisters labeled for reclamation) by licensed repair shops abiding by EPA regulations since they're likely to perform many repairs to vehicle ac systems. However, in reality, leaks release refrigerant that no one can control when it occurs. Again, refrigerant must be removed before repairs begin as standby pressures (ac off, ambient temperatures) vary more or less direct proportion to outside temps. 75F/75 psi, 95F/95psi - sealed system pressures. When running, high side pressures can easily exceed 200 psi - not diy friendly when attempting to monitor pressures without familiarity about hazardous conditions around working ac systems. The two service valves are for anyone familiar with using gauges and the eventual repairs needed when ac fails. Disconnecting any ac fitting without understanding standby pressures can result in an immediate high pressure (approximately 75 psi) discharge of refrigerant and oil to blind anyone not wearing eye protection. It's said that FAA regulations related to flying are paid by the blood of accidents and crashes and the investigations to uncover the causes and make recommendations to prevent repeating mistakes. Vehicle ac repairs are no different with safety procedures already well known to allow anyone a safe procedure when working on ac problems.

Because sealed ac systems will leak, eventually, knowing what refrigerant remains determines if its safe to open fittings with an empty system or removing the bulk of it into a reclamation canister using gauges and (electric) vacuum pump. Repair shops not using reclamation canisters can be fined thousands of dollars for allowing release of refrigerant into the atmosphere. Diyers discovering their empty systems already released refrigerant are generally not subject to being cited for inadvertent leaks. Once a system is depressurized, fittings can be safely disconnected. Since oil circulates freely throughout a system, you're likely to find oil (and dye if installed at factory assembly) on your hands. Repairs must be kept clean to prevent debris from getting into a system that can accelerate compressor wear. R134a O-rings are prelubed with r12 mineral oil - it doesn't absord moisture.

Once you become familiar with diagnosing and troubleshooting your system, the reason for replacing seals may not be as simple as it appears. R134a systems use pag oil that readily absorbs moisture. A leak will release refrigerant, dye and oil, attracting moisture to the leak area. Moisture will begin to corrode bare, untreated aluminum parts in every ac system. This can erode the precise fitting surfaces in each fitting that mates to allow the O-ring a leak free seal. Corrosion allows uneven protrusions preventing proper sealing against pressures. Fitting faces should be at least free of any corrosion preventing re-sealing with new O-rings. Guess how I know? Overtightening of aluminum fittings or replacing seals will not correct for corrosion. Remember, fittings on the high side (discharge side of compressor, hose, condenser coil, receiver/drier, hose to input side of the thermal expansion valve, will be under pressure between 125-250 psi. While ac systems are not rocket science, familiarity is needed to work on them. I like the analogy; if you do not understand super or turbo chargers, then it's not a diy friendly repair if it breaks down. The same for vehicle ac systems.

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  • yah I watched the whole video and did note the comment you reference above from JVG the tech. What I couldn't tell from his comment is the volume of refrigerant he was referring to or which could be at play. That wasn't communicated really, so I wasn't sure if it was some residual pressure remaining just in the compressor but that the bulk of the refrigerant would be locked behind some valve I was imagining could possibly be present, or if there was no protection and the bulk of the refrigerant would go free. That uncertainty is what triggered this question.
    – jxramos
    Aug 24, 2023 at 20:56
  • This is good terminology to know about standby pressures, that's what we're fundamentally talking about and realizing is present in the AC system. There's standby pressure just sitting there waiting for the next AC cycle to begin.
    – jxramos
    Aug 24, 2023 at 20:59
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    As another diyer, I went to my local library decades ago and borrowed a book on refrigeration. While I can claim one cell between my ears, my learning curve started there and finding a perfectly good refrigerator compressor for my first vacuum pump. Buying my first set of gauges (r12) set me on a long path to learn diagnosing, troubleshooting and repairing vehicle ac systems. I would strongly suggest anyone to do the same as refrigeration is not diy friendly when information is available everywhere to learn the basics. Basic building blocks of learning before jumping into the deep end.
    – F Dryer
    Aug 24, 2023 at 21:10
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    @jxramos - I don't think you are getting the meaning of "standby pressure", at least it doesn't seem so from your comment. Yes, it's pressure in the system, but it is the same everywhere in the system after equalization. Please realize the AC system is basically one big loop with restrictions in it. When the pump isn't moving, the system moves towards equalization throughout. It's simple physics. The high pressure moves towards the low pressure until it's all happy. Aug 24, 2023 at 21:40
  • yah, I'm thinking isobaric pressure through every point in space in the entire loop for the specific condition where the car is parked and the engine off and at ambient room temperature. There's still pressure in that condition correct? –
    – jxramos
    Aug 24, 2023 at 22:13

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