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1086 ac vacuum leak rate?


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What's an acceptable leak rate under vacuum?

Installed all new hoses and compressor and drier.  It pumps down to 30 pretty quick, but leaks back up to 10 in less than 30 min.  Pretty positive the valves are losing some, maybe more than the rest of the system.  But I still think something in the system is leaking.

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What we taught at school is 500 microns on a brazed system should hold for more than 5 minutes with out a change in the vacuum. Bolted semi hermetic ( what you have) is 1000. Now you can not measure that with a gauge set because that is more than 29.9 inches of vacuum. Two things; If the vacuum rises to 10 in a 1/2 hour you should be able to pressurize with dry nitrogen and easily find the leaks. If it held closer to 30 on a gauge set and really slowly came up (a very long time) there is moisture in the system and the pump needs to run longer. Might even have to change the oil in the vacuum pump. I taught the students to check the pump first as that will dictate if the pump is capable. I did not see any mention of a micron gauge which really is an essential to do it right, gauge sets can be off quite a bit. Any moisture can and will cause the system to freeze at the expansion device causing intermittent problems. Do you have dry nitrogen? does it hold pressure (120-150)for 10-15 minutes. To me mobile A/C is frustrating as it is easy to pull what you think is a good vacuum but the seals will not hold on the compressor. If you are looking for temporary cooling the old Triple evac is the way to go but is frowned upon by EPA. And yes but I have done this for years is not a professional excuse, as I have seen people do this before and seem to get by. You asked for the proper way and that is it. Myself it appears you have a fairly large leak yet. Did you use an approved oil on the thread and O-rings that will help.

Edited by VacDaddyt
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Basically all fittings except for two or four,  are flare fittings.  Just regular cheapo guage set, in inches of vac.  I certainly could have made something worse, but it worked ok prior maybe not great but good enough.

Had it pumping for half an hour, and overall longer than that.  Checked fitting tightness, everything seems tight.

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 First of all how are you closing the vacuum off from the pump? At the red and blue valves or at the pump? I have seen the valves on pumps leak. That is why I am recommending a standing pressure test. Try this ;put only the gauge set on the vacuum pump capping the ports just below the manifold with caps that have O-rings ( is this a 134 set). Open both red and blue valves and let pump run. Valve off the pump and see if it changes. I have made up adapters to use refrigeration gauges so I have multiple ways of doing this. I have made a fitting with both high side and low side into a t to check my gauges. A ball valve is really nice in this situation. What ever you do not use regular air to pressurize as it only adds more moisture to get out. Oh and I oil flares also makes them seal easier. Did you use a new expansion device? One other thought did you open both sides when on the vacuum, low and high? It could be only one side was open and the expansion valve keep both sides from equalizing and there is nothing wrong. Been there a few times and usually caught the problem when it did not seem right.

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1 minute ago, nelson jr said:

So if mine comes up four inches in five minutes, that's essentially a hundred times worse than what you said it should be. Right?

Yes

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 I would be willing to bet it’s the hoses’s on your gauge’s that are causing your loss of vacuum . 

 Pressurize your hoses and put them under water you may be amazed at how many bubbles you see .

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Completely reworked the ac on one of my 5288s last year. Everything was new ; hoses; compressor, etc. Would not hold pressure. Found out it was the o rings and the fact that I had overtightened them. Local ac guy at the Case IH dealer said any fittings you put those little green o rings in should only be snugged. Overtightening compresses them too much allowing leakage.

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3 hours ago, nelson jr said:

So far the gauge hoses leak, and the valves on compressor leak.  Thinking about tearing one of the valves apart to see if they could be rehabed.

Valves on gauges can be taken apart. I have found metal chips from manufacturing in the Teflon. Might be able to get them to seal. Good start for you.

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I was talking the valves on the compressor.  Got a wee little bit of time in the morning, and then it's hook up and mow hay time.  I never pictured this job taking so long or this turn of events.

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2 hours ago, nelson jr said:

I was talking the valves on the compressor.  Got a wee little bit of time in the morning, and then it's hook up and mow hay time.  I never pictured this job taking so long or this turn of events.

If your talking about the service valves you can do away with them with a kit. I've had lots of trouble with them as well

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