Boiling temp of water at converted pressures

[Tom Greenleaf]

This is in archives of once just called ACSource.com forums, useful here I hope,

[Cornbinder89]

What I find most telling about this is: 29" of vacuum isn't going to get the moisture out. As it changes from liquid to gas, it absorbs heat just like any refrigerant, and unless the temp is really high, you need a much higher vacuum, around 29.4" and most compound gauges are just not good enough to see the difference between 29" and 29.4". you really need a good pump and a good vacuum only gauge to tell.
Most times its good enough to let the pump run then watch for a rise in vacuum, but for that troubled system, you can't be sure the moisture is out. It is why they used to recommend 3 sweep charges, vacuum, then add a bit of refrigerant, and vacuum again, and repeat.

[Tom Greenleaf]

Hope that's the chart you once mentioned you were looking for. ACSource shut down a couple times and it may have been lost and showed again. Point is so important - water=moisture MUST be out. Everything has to be considered - the air in hoses. What the vehicle was exposed to and how long it's been All of it.

Altitude - I need to find a chart for that and see if I/we can get some of this all together like a reference book of critical info.

It's is startling to look at 29 Hg even and what the fractions do as you deviate from just that.

I suggest vehicles be warm and working on them while warm. Repeat as needed.

What can really matter if you have found and fixed a leak or have a leak found with just this the air ruining your vacuum is yet again full of moisture!

[Cornbinder89]

It really points out that if you have a troubled system, you can't just rely on the compound gauge and a vacuum pump to KNOW that you have the system dry. The difference in boiling point between 29" and 29.8" is vast, but the amount of movement on a compound gauge is just a hairline.
My older text book recommends 3 "sweep" charges to remove the moisture, but today I would guess you would use three sweeps of dry nitrogen rather than refrigerant.
An electronic vacuum gauge and lab spec vacuum pump would do the job in one pull, but used lab pumps (the type we are likely to afford) may be so worn as to not pull enough either. Normal A/C pumps, single or two stage would struggle to get in the high 29" range, but are fine for systems that don't have a lot of moisture, what ever they don't pull out by vacuum, the little left can be handled by the desiccant in the drier. A/C vacuum pumps main job is to get all the non-condensable gas out of the system, it does a less good job of getting moisture out.

[James Wade]

Thanks for the information about the boiling temperatures of water at converted pressures, I was just looking for it