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Clarification of Vacuum and Charging Procedure

69-er on Tue June 22, 2010 4:09 PM User is offlineView users profile

I don't know where I heard this, but I think the "Vacuum and Charging Procedure" in the Tips and FAQs section touched on this.

If, after evacuating a system and then turning off the pump for 5-10 minutes produces a drop in vacuum, does this indicate there is still moisture in the system? If so, does this mean as moisture is boiled off, the moisture is displaced by showing this drop in vacuum? This is assuming there are no leaks, of course.

Also, where does this boiled off, (evaporated?) moisture go? I can't see it being sucked into the pump, as there is no air flow to produce a movement for the moisture to travel with.

Thanks!

Briandl79 on Tue June 22, 2010 6:23 PM User is offline

Never heard that but I guess I didn't read that post. I always thought a drop in pressure was the result of a leak.

What happens if you vacuum it again, does it leak off after 5-10 minutes again? That would indicate to me that the theory is invalid, or you have a shit ton of moisture in the system.

How long are you running the vacuum? Make sure all of your lines are tight.

HECAT on Wed June 23, 2010 7:07 AM User is offline

Yes, if you do not pull hard enough and long enough and then stop and hold; refrigerant in the oils, moisture, etc can continue to gas in the vacuum environment and decay the vacuum reading. The vacuum environment induces these undesirables to gas and with the vacuum pump running they are evacuated by the pump.

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NickD on Wed June 23, 2010 8:19 AM User is offline

They say a watched pan never boils, but that is not true, if you don't die of pure boredom first. Water does boil in a vacuum at about 77*F, but likewise, it is not instantaneous.

Prevention is always the best medicine, should do all your AC work in a 0% RH room, but if that isn't possible you have a variable and a guess is all you have as to how long to vacuum. And that moisture will boil faster in a 100*F environment that a 77*F one, but not at all if below that temperature, but even below that temperature, it will evaporate. This is getting way too complicated, so can run your pump for three hours and take a nap.

If you hook your vacuum pump to a power meter, will quickly learn its only doing work for the first few seconds and really sucking the power. After that, the power drops to almost nothing as it is not actually doing work, so let that run. With my own cars, like to run it for three hours, for my brother-in-law, five minutes is enough. He will more than likely smash that car up before he has AC problems. You will also want to replace the dryer, those are one shot deals, too bad they don't make them so you can just replace that bag, pitching an otherwise good receiver or an accumulator seems a waste.

Yes, if given time, as more moisture evaporates, will see a slight drop in vacuum, but that is not the only cause of the vacuum dropping. Single lip seals seal much better with lots of pressure behind them then being sucked in the opposite way by a vacuum. Those quick coupler R-134a ports, at least in my opinion and experience are pure unadulterated crap when compared to the R-12 Scharder valve type where you can get a good seal.

Maybe thinking about the good old days is a wild dream today, but just don't recall having the problems like we are having today in drawing a vacuum, would always hold, and if there was a little moisture, who cared, R-12 could live with the, R-134a cannot, forms an acid that can be highly destructive. But I know paying 25 cents a pound for R-12 was not a dream. Neither was paying cash for an airline ticket five minutes before the plane took off. And back then, was no such thing as an EPA, when they were created, stood far away from AC until about 1993, that is when the nightmares started. Are they really doing any good????

So in consequence, if that pressure does drop, is it moisture or EPA induced leaks? Only way to really learn is to do a pressure test first, another step, more inconvenience, more time, more guessing, more worry about getting fined.

CCWKen on Wed June 23, 2010 10:17 PM User is offlineView users profile

Get yourself an old pickel jar and add a fitting to the top. Spray-mist a few sqirts of water into the jar and tighten the top to the jar. Attach a vacuum line to the fitting and start the pump. You'd be supprised at how fast the water disapears. For safety's sake, place the jar in a bucket in case it implodes. It shouldn't but there may be a crack or chip somewhere you missed.





-------------------------
Ken Kopsky

Custom Car Works
"Rules are for the guidance of wise men and the obedience of fools."

CCWKen on Wed June 23, 2010 10:21 PM User is offlineView users profile

Forgot to mention: It's always good to let the pump run for extended periods. This not only assures a complete evacuation of the moisture but also heats your pump oil to evaporate moisture from the process.

-------------------------
Ken Kopsky

Custom Car Works
"Rules are for the guidance of wise men and the obedience of fools."

Rick-l on Thu June 24, 2010 3:18 PM User is offline

Quote
Originally posted by: NickD


If you hook your vacuum pump to a power meter, will quickly learn its only doing work for the first few seconds and really sucking the power. After that, the power drops to almost nothing as it is not actually doing work, so let that run. .

If that is true how come my pump gets so hot after 30 minutes?

Dougflas on Thu June 24, 2010 5:23 PM User is offline

Also, change your pump oil regularly.

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