Auto A/C Repair Question
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50 micro vacuum == 50mm mercury vacuum. "In vacuum systems, the units torr, micrometre of mercury (micron), and inch of mercury (inHg) are most commonly used. Torr and micron usually indicates an absolute pressure, while inHg usually indicates a gauge pressure." Wiki[^]
Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water
I wouldn't bother. He never listens.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^] English League Tables - Live
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What the heck is a 50 micron vacuum? A micron is a measure of distance, not pressure! :confused: So if the specs call for running the vacuumm pump for 30 minutes after the system reaches a certain vacuum just run it for 45 minutes or an hour. Surely itf will have got to the right vacuum and do the job. However, I find it odd that putting the system into a near zero pressure state is going to remove any debris, I would have thought a back flush would be best.
============================== Nothing to say.
Distance => pressure/vacuum is common. Typically the height of a mercury column the pressure would support (1 atmosphere is approx 30" or 760mm). mmHg is a common pressure unit. So Roger's target is effectively 0.05 mmHg pressure, or about 6.5 pascals. Also, the aim of evacuation is to remove residual (non-refrigerant) gases, not particulate crud. Cheers, Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
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Distance => pressure/vacuum is common. Typically the height of a mercury column the pressure would support (1 atmosphere is approx 30" or 760mm). mmHg is a common pressure unit. So Roger's target is effectively 0.05 mmHg pressure, or about 6.5 pascals. Also, the aim of evacuation is to remove residual (non-refrigerant) gases, not particulate crud. Cheers, Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
I did the Kessel Run in under 12 Parsecs.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^] English League Tables - Live
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Since this eclectic lot have such a diverse background, I thought I'd toss out a question for the group. I have a depleted A/C system running R134a[^] as a refrigerant. I've replaced the compressor, which was known to be bad, and plan to replace the accumulator and orifice tube this weekend. Before doing that, however, I intend to vacuum the system after a good flushing to remove any shrapnel left behind when the original compressor died. I have in mind a 5 CFM vacuum pump that will do the job, but I can't find any guidance about how long I should let it run before refilling the system with very expensive refrigerant. Specs call for maintaining a 50 micron level of vacuum for 30 minutes, but I have no clue how to calculate how long it will take the pump to reach the 50 micron level, and I can't afford the $300 cost of a vacuum gauge, nor the 2 week wait to order such a beast. It's already 115°F here, and not likely to get any cooler for 4 - 5 months, so I can't really wait for deliveries. Can someone provide, from a textbook or practical personal experience, some guideline as to how long I should run the vacuum pump before starting the 30 minute timer? If it matters (and it probably does), the system capacity is 5 lbs of R134a refrigerant. Thanks, guys and gals, for any wisdom you might impart...
Will Rogers never met me.
Are you saying you don't have any gauges at all? What are you using for a charging manifold? You have had the system apart - that means the possibility of leaks. The only way to test for this is to draw down a vacuum in the system and to see if that vacuum holds. The way to measure this is with a vacuum gauge. To vac the system should only take an hour or so. The longer you vac (run the pump) the more moisture is removed. When the pump is stopped read the gauge. Leave the system for some hours to be certain of your results. A gauge that changes quickly indicates a big leak. A small leak may take many hours even overnight to detect.
Peter Wasser Art is making something out of nothing and selling it. Frank Zappa
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Since this eclectic lot have such a diverse background, I thought I'd toss out a question for the group. I have a depleted A/C system running R134a[^] as a refrigerant. I've replaced the compressor, which was known to be bad, and plan to replace the accumulator and orifice tube this weekend. Before doing that, however, I intend to vacuum the system after a good flushing to remove any shrapnel left behind when the original compressor died. I have in mind a 5 CFM vacuum pump that will do the job, but I can't find any guidance about how long I should let it run before refilling the system with very expensive refrigerant. Specs call for maintaining a 50 micron level of vacuum for 30 minutes, but I have no clue how to calculate how long it will take the pump to reach the 50 micron level, and I can't afford the $300 cost of a vacuum gauge, nor the 2 week wait to order such a beast. It's already 115°F here, and not likely to get any cooler for 4 - 5 months, so I can't really wait for deliveries. Can someone provide, from a textbook or practical personal experience, some guideline as to how long I should run the vacuum pump before starting the 30 minute timer? If it matters (and it probably does), the system capacity is 5 lbs of R134a refrigerant. Thanks, guys and gals, for any wisdom you might impart...
Will Rogers never met me.
Roger Wright wrote:
It's already 115°F here, and not likely to get any cooler for 4 - 5 months, so I can't really wait for deliveries.
But it's a dry heat! Seriously, I don't think man is supposed to live there, in part because that environment doesn't support man.
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Distance => pressure/vacuum is common. Typically the height of a mercury column the pressure would support (1 atmosphere is approx 30" or 760mm). mmHg is a common pressure unit. So Roger's target is effectively 0.05 mmHg pressure, or about 6.5 pascals. Also, the aim of evacuation is to remove residual (non-refrigerant) gases, not particulate crud. Cheers, Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
Yeah. Used to hate pumping down the cryo LNAs. Took for-freaking-ever and sometimes never reached the spec, so had to tear them down and try again. But at least having huge bottles of helium around was fun. I hope no MiG ran into any of the trashbags we sent aloft.
No dogs or cats are in the classroom. My Mu[sic] My Films My Windows Programs, etc.
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I did the Kessel Run in under 12 Parsecs.
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^] English League Tables - Live
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Are you saying you don't have any gauges at all? What are you using for a charging manifold? You have had the system apart - that means the possibility of leaks. The only way to test for this is to draw down a vacuum in the system and to see if that vacuum holds. The way to measure this is with a vacuum gauge. To vac the system should only take an hour or so. The longer you vac (run the pump) the more moisture is removed. When the pump is stopped read the gauge. Leave the system for some hours to be certain of your results. A gauge that changes quickly indicates a big leak. A small leak may take many hours even overnight to detect.
Peter Wasser Art is making something out of nothing and selling it. Frank Zappa
I have charging gauges, but they're not much use in high vacuum. The special vacuum gauges are pricey, and I don't expect to need one again. The system was charged, but not enough to work; injecting UV dye showed a leak, which was repaired, but adding more R-134a was impossible, as the compressor was shot. I replaced the compressor, but after some thought, decided that it would be smarter to replace the accumulator and orifice tube, as well. They're cheap, and if any bits of compressor got into the system, that's where they'd lodge. So I plan to replace them, flush the system, then dry the thing out with vacuum before recharging it. I just haven't a clue how long to run the compressor without a vacuum gauge, and don't want to buy one. :-D
Will Rogers never met me.
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Roger Wright wrote:
It's already 115°F here, and not likely to get any cooler for 4 - 5 months, so I can't really wait for deliveries.
But it's a dry heat! Seriously, I don't think man is supposed to live there, in part because that environment doesn't support man.
wizardzz wrote:
that environment doesn't support man.
Yes, but it does support beavers, and where there are beavers, men will come.
Will Rogers never met me.
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I have charging gauges, but they're not much use in high vacuum. The special vacuum gauges are pricey, and I don't expect to need one again. The system was charged, but not enough to work; injecting UV dye showed a leak, which was repaired, but adding more R-134a was impossible, as the compressor was shot. I replaced the compressor, but after some thought, decided that it would be smarter to replace the accumulator and orifice tube, as well. They're cheap, and if any bits of compressor got into the system, that's where they'd lodge. So I plan to replace them, flush the system, then dry the thing out with vacuum before recharging it. I just haven't a clue how long to run the compressor without a vacuum gauge, and don't want to buy one. :-D
Will Rogers never met me.
OK you're in business. Using the gauges you have vac the system for a couple of hours. Then close the pump line off and monitor the gauge. If it holds its reading for a couple of hours then charge the system. If the vac pump is in good condition you'll be fine. It's many years since I did this for money but we did not have high vac gauges.
Peter Wasser Art is making something out of nothing and selling it. Frank Zappa
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Roger... Email this person ( jonathancostigan @ adcock . co . uk) and ask him. Mention my name, he is my brother and is a Refrigeration Engineer, if he can't help you, no-one can!
--------------------------------- I will never again mention that I was the poster of the One Millionth Lounge Post, nor that it was complete drivel. Dalek Dave CCC Link[^] English League Tables - Live
Thanks, Dave!
Will Rogers never met me.
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OK you're in business. Using the gauges you have vac the system for a couple of hours. Then close the pump line off and monitor the gauge. If it holds its reading for a couple of hours then charge the system. If the vac pump is in good condition you'll be fine. It's many years since I did this for money but we did not have high vac gauges.
Peter Wasser Art is making something out of nothing and selling it. Frank Zappa
Thanks, Peter. As a matter of fact, I ordered the pump today, so it ought to be in good condition. :-D That's why I can't also afford a vacuum gauge right now... :doh:
Will Rogers never met me.
