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Old 08-19-2009, 07:14 PM   #1
jonnycube
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Default Completely hypothetical AC question

I cannot overemphasize how extremely hypothetical this question is.

Let's say you have a completely working AC system in your car, and some dunderhead decides to unbolt the high pressure AC line. I don't mean remove the cap to the service valve, I mean unbolt where the line connects to the compressor, causing a geyser of refrigerant to erupt into the air. Let's say this dunderhead then quickly secures the bolt again.

What would this do to said dunderhead's AC system? Since the system is still sealed, would it require a simple recharge, or has something likely been damaged?

This is fictitious and has absolutely nothing to do with reality. Seriously.
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Old 08-19-2009, 08:13 PM   #2
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Default Re: Completely hypothetical AC question

Usually when a stunt like that is pulled you loose the oil along with the refrigerant. You should check the residual system pressure and if any positive value then you can add the nominal recharge of oil and refrigerant. The amount of oil loss is the big unknown. As this is all hypothetical, I am setting the condition that the system was not in operation when the high side was opened and the o-ring did not blow out.
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Old 08-19-2009, 08:23 PM   #3
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Default Re: Completely hypothetical AC question

Even a dunderhead wouldn't be so foolish as to try such a trick while the car was running. Fortunately.

In our story, the AC system still has pressure. The compressor clutch engages. Refrigerant/oil was added from an EZ Chill canister until the low pressure line reached about 50 psi in 85 degree weather. The car then blows very slightly cool air from the AC. Not cold, and barely even cool, but not warm or hot, certainly. What is our fictional hero to do?

Fdryer, I just want to preemptively state that this hypothetical person was not looking for a "quick fix". Since the system was fully functional and has no leaks, there should be nothing wrong with simply recharging it.
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Old 08-19-2009, 09:18 PM   #4
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Default Re: Completely hypothetical AC question

well, when the entire car has reached ambient temperature, as in setting all night, the system pressure with the compressor off will be close to the ambient temperature when properly charged. To continue to charge the system you heat the can of refrigerant in hot water and inject refrigerant as liquid into the system in small shots, all with the car and compressor off, until you get system pressure to be slightly below ambient. The introduction of the warm liquid will cool the system as it expands to a gas and give a false low pressure reading. Make haste slowly and allow the temperatures and pressures to stabilize. This can take 15 to 30 minutes. The problem with this little trick is you really have no idea of how much refrigerant is in the system. Right now you are low but if not careful you can get way too much in without having any big symptoms of high pressure. The only practical way to get the refrigerant back into the system from the little can is by heating the can and injecting as liquid. Figure you will be adding liquid in 2 to 4 oz shots and it will not take many. As there is some cooling the system components are functioning and the weight of refrigerant in the system presently is close to the correct weight. This process takes a while to do right.

This is all hypothetical of course and not a recommended practice.

What happens if you get too much refrigerant in the system is that it is returned to the compressor suction as liquid and liquid refrigerant is non compressible. It is a positive displacement compressor and that will blow the rupture diaphragm on the back of the compressor. There is not a lot of margin between OK and way too much.
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Old 08-19-2009, 10:08 PM   #5
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Default Re: Completely hypothetical AC question

I almost follow what you're saying. Almost.

Here's my question. You make it sound like the system is simply low on refrigerant. Why does the process of adding more need to be different than the instructions on the bottle? i.e. run the car with the AC on max for three minutes and release refrigerant into the low side port while shaking until the pressure reading is right. The instructions said that in 85 degree heat you should aim for between 45 and 55 psi. The person in the story took it to 50.

This fake person is understandably wary of overcharging the system. If he got the pressure where it needs to be, how can it still be low? Why is there no cold air?
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Old 08-19-2009, 10:43 PM   #6
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Default Re: Completely hypothetical AC question

I have a question on the "oil".

Is it mixed with the refrigerant? Seems like a "yes" answer. So if you release refrigerant, you also release oil?
Can you buy oil to add?
Ok then... suppose you add some oil, then refrigerant. What if you add too much oil? Or too little?

Roughly how much A/C oil would be in my Saturn?
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Old 08-19-2009, 11:03 PM   #7
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Default Re: Completely hypothetical AC question

The instructions on the can relate to a CCOT system, Cycling Clutch Orifice Tube. The Saturn uses a variable displacement compressor and a Thermal expansion valve. Does not work the same way. This is why everyone gets burned when they try and read the high and low side pressures while referring to the handy dandy DIY generic Fix the A/C book.

In this hypothetical situation what is trying to be accomplished is to get the static system pressure up to something that is close to a full charge. That should generate cold air with minimal probability of testing the compressor relief. So, you add liquid until you have slowly increased the static system pressure to equal the ambient temperature. As the liquid addition cools the system you have to wait for it to return to ambient. As there is 50psi in ther now you will never get enough into the system by injecting gas. And, even injecting gas will cool it off. When the charge is close to correct the compressor will promptly shift to minimum displacement and the suction pressure will increase to the point that can pressure is equal to system pressure.

Static implies that both the engine and compressor are OFF.

This is why to properly charge a Saturn system you evacuate it and then inject a known weight of refrigerant. There are other methods that work with the CCOT systems but Saturn is not one of them. Under static conditions the system is at saturation conditions and when the pressure is close to the temperature for R-134a a slight pressure decrease results in all gas and a slight pressure increase results in liquid in the system. The compressor is the mechanism of changing state from gas to liquid and liquid to gas.
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Old 08-19-2009, 11:09 PM   #8
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Default Re: Completely hypothetical AC question

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Old 08-19-2009, 11:11 PM   #9
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Default Re: Completely hypothetical AC question

Quote:
Originally Posted by MikeNW View Post
I have a question on the "oil".

Is it mixed with the refrigerant? Seems like a "yes" answer. So if you release refrigerant, you also release oil?
Can you buy oil to add?
Ok then... suppose you add some oil, then refrigerant. What if you add too much oil? Or too little?

Roughly how much A/C oil would be in my Saturn?
The normal full charge of oil is 150cc of PAG oil. If you experience a rapid depressurization event you add 90cc of PAG oil back into the repaired system to replace what was lost.
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Old 08-19-2009, 11:34 PM   #10
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Default Re: Completely hypothetical AC question

1-dunderhead loosens high pressure fitting releasing geyser and quickly tightens fitting.

What was released and how long? Besides R134a, any oil spray leaving its mark anywhere or was there a fine mist like spritzing? If things worked before and this dramatic lesson displayed what a pressurized system holds, does the system still cool? If the a/c system still cools, dunderhead should leave well enough alone. The question not asked was if the system still cools.

2-Refilling for any reason is simply not done at idle speed and a presumption is made on my part that 99% of DIYers attempt recharging at idle. The 1% that have some familiarity by researching and asking forums like Saturnfans or the few real a/c forums will find out that set procedures are described and one of the procedures is running 2k rpm for the refill. Gauges are used. Pressures are invalid at idle rpm. All pressures are read at 2k rpm. Getting this far will indicate the complexity of refrigeration as pressures vary in proportion to rpm. Not rocket science but not something everyone wants to know so confusion begins. To do so at idle speed can work if you're patient, ill informed, and don't have a clue as to what's going on in a refrigeration system. I cannot help myself but to use and repeat the public service announcement, "the more you know....".

dunderhead should search for a member that wrote an extensive two-part procedure using all the a/c equipment necessary to do repairs properly when a system is opened. <jerry hughes>
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Last edited by fdryer; 08-19-2009 at 11:41 PM.
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Old 08-20-2009, 01:19 PM   #11
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Default Re: Completely hypothetical AC question

The fitting was released for 10 seconds at most before it was tightened again. The AC system was not touched for a week or two after this for fear of damaging the compressor from a low oil level. After the recharge can, only a pitifully cool air comes from the AC. Not cold. Not warm or hot. Just slightly cool.

It's a shame the bottle doesn't say anything about testing pressure at a higher RPM. Anyone purchasing said can would think that by following the directions they are sure to succeed. That's very misleading.

So you won't get an accurate reading unless the car is doing 2000 RPM, and in addition to that, Saturns use an unusual kind of compressor and expansion valve. I'll take your advice, Fdryer, and look up that extensive two-part procedure. You know, in case I run into anyone stupid enough to ruin their AC in this manner.

What I'm wondering now is, if refrigerant has already been added the wrong way, is it safe to add more the correct way, i.e. putting the can in hot water as OldNuc suggested? Since the system is already at the psi level it's supposed to be, isn't it a bad idea to add more? Is it necessary to discharge some of it (properly, of course)? Or, since it was filled with the RPMs too low, will the gauge read lower when the RPMs are at 2000, thus allowing room to add more properly?
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Old 08-20-2009, 02:27 PM   #12
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Default Re: Completely hypothetical AC question

The 2k RPM is only listed as a defined test point. It is not magic. The pressures specified in teh manual that are taken as being delivered on stone tablets on a mount are based on teh very important assumption that the system contains 150cc of PAG oil and 24 oz of nice clean R-134a.

These are not the conditions in which your hypothetical person finds themselves. The question that was originally asked was how do you get out of this mess without spending several hundred dollars (more than 200 most likely) to comply with the Fed EPA requirements to get the system squared away. You can not force fit the FSM specs to the existing conditions. There are several ways to skin this cat and they all work. Some carry a higher potential for implementation error than others. If you hypothetical person tries to play the 2K RPM gauge reading exercise and inadvertently overcharges the system the risk of liquid in the suction is real.

Your hypothetical situation is beyond the scope of the standard procedures. There is an old expressions that pertains here; No B**ls, no blue chips. The blue chip is the high dollar chip down at your favorite local casino.
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Old 08-20-2009, 03:21 PM   #13
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Default Re: Completely hypothetical AC question

What most likely occurred before all these hypothetical issues appeared was a leak that occurred to this hypothetical system that lead to inadvertently releasing R134a for the wrong reasons.

I'm not sure if Oldnuc was trying to explain it clearly but refrigeration is refrigeration; there's a low pressure side and high pressure side that's established when engine rpm's are raised to monitor pressures (2k rpm according to most manuals). Not having familiarity with the inherent dangers of a/c system pressures and knowing in advance what to expect if never opening a book on refrigeration will confuse anyone and generate more questions than necessary, some almost beyond comprehension. If a fitting were to be left open for longer than a few seconds and high pressure refrigerant was seen to be released with little to no cooling afterwards, only a set of gauges attached to both service valves can assess what's going on internally. Both pressures needs to be monitored in order to determine what pressures exist. And the engine rpm must be at 2,000. An analogy (without going into the science of refrigeration) to running 2k rpm is that you don't drive at idle speed so why are you measuring pressures there? A/C systems running at 2k rpm are at ideal operating conditions where best cooling takes place, even better when actually moving the car through the air as the front of the car is getting forced air into the condenser and radiator for better cooling effects. For arguments sake, liability issues are raised if the cans instruct everyone to run their engines at 2k rpm and ignorance comes into play with a car engaging gear resulting in an accident. Far too many inept drivers will blame others for their misfortune instead of admitting ignorance to safety precautions. 'nuff said.

No one can add R134a incorrectly, not even dunderhead; the service valves prevents feeding gas or liquid into vehicle systems due to different sizes for each valve so adapters cannot fit into the wrong valves. Whether filling R134a as a gas or liquid doesn't change where it enters. Liquid filling is quicker but can cause compressor damage if done incorrectly; liquids are incompressible and if feeding liquids into a compressor trying to compress a fluid, fluids cannot be compressed so something mechanical gives - the compressor. Liquid feeding is done by persons familiar with refrigeration and not casually offered to anyone without prior knowledge. This goes beyond normal information and only experienced persons can use this 'liquid filling routine'. Getting this far into systems requires a manual for all the information to fully understand what's involved. Look at refrigeration with the same complexity as adding a supercharger or turbocharger; if you don't think you're good enough to add turbocharging to your car don't presume a/c systems are easier. If you don't work on your refrigerator, what makes you think you can work on your car airconditioner? Airconditioning is airconditioning, whether its the room unit or your car.
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Old 08-20-2009, 05:45 PM   #14
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Default Re: Completely hypothetical AC question

I think you misunderstood how completely foolish the person in this story is. There was no leak. The AC was perfect. Disconnecting the hose from a pressurized system was a totally random stupid mistake. The AC system wasn't even being worked on.

Let me try to summarize. This is not a simple fix. The only encouraging part of the story is that the system is sealed - there is no leak. I shouldn't have to replace the dryer. If I pull a vacuum and add the correct amount of oil and refrigerant using the correct method, with the engine running at the right RPM, all will be will. My mistake was thinking that one of those dumb cans would work, since nothing is leaking.

Yes, I'm speaking in first person. All this hypothetical stuff was becoming tiresome.
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Old 08-20-2009, 06:22 PM   #15
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Default Re: Completely hypothetical AC question

Drawing a vacuum does not remove the oil that is in the system. However, drawing a vacuum can result in the TXV sticking closed. If you choose to go that way pay someone who has Saturn experience or you will have more problems.

Or you can increase the static pressure to match the ambient temperature by any of a half dozen methods and that will probably fix it.
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Old 08-20-2009, 10:15 PM   #16
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Default Re: Completely hypothetical AC question

How would drawing a vacuum cause the TXV to stick close? A properly operating TXV is controlled by temp, hence the T as thermal. When the system is not running the TXV should be wide open.
The only time I have ever seen a TXV stuck shut the temp sensing part was broke
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Old 08-20-2009, 10:36 PM   #17
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Default Re: Completely hypothetical AC question

For what ever reason the Saturn Thermal eXpansion Valve does stick shut. Happens often enough that the usual routine from the rebuilt compressor places is that the warranty is void if you do not replace the TXV and dryer with the compressor. To establish flow you have to way overcharge the system and then knowing how much extra you injected you recover it.
The compressor will sit at minimum displacement with no system flow until the compressor fails from lack of oil when the TXV sticks shut. Does not happen every time but often enough. Having to do this and end up at the correct charge makes this a difficult DIY exercise with the normal tools. There are 12 pages of high side/low side pressure charts in the HVAC section of the FSM and you need all of them.
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