[wwest]

Originally Posted by kuehl

The terminology 'hard' vacuum is not quantitative;

So let's just consider it a generic, non-definitive term, that will be understood by the public at large, okay?

there are arguments that state a hard vacuum is 1 Torr while others state it at .01 Torr.

It is easier to refer to vacuum in terms of either Torr, Microns, or Inches of Mercury; these terms are more commonly found on the gauges, equipment and charts used in AC.

Is it 'practical' to attempt to evaporate or remove all of the moisture in a water soak drier? No, because it is possible to pull a vacuum down deep enough, quick enough, that water liquid turns into a solid (ice) before it 'evaporates' or is removed by the vacuum procedure.

Assuming the OAT at the "evac" location is well above freezing the only "cause" for the water freezing would be the evaporativer rate of the water itself....

So, yes, a QUICK/DEEP vacuum might well result in freezing a portion of the water in the desiccant....but for how long...?? All of 30 seconds..??

Just remembering the old 7th grade science class trick of freezing a drop of water under a thin glass bowl via rapidly evaporating a bit of ether in the bowl...and how long that water didn't remain frozen in the classroom environment.

And, another issue not often discussed in terms of an evacuation procedure, is for instance when converting from R12 to R134a: for those whom attempt to save a few dollars by not replacing the drier with a new one. Refrigerants become trapped within the refrigerant oil within the drier. Hence, if you think you recovered or evacuated out all of the R12 prior to inserting in R134a, you will be surprised to find that you have not. Refrigerants can remain entrapped within the oil in the drier.

Once again, just what is the detriment in having a small/meager amount of R-12 remaining in the system post evacuation and refill with R-134a.

What would be the "surprise"? How might you EVER know, discover?

So, it is SOP, to replace a drier when it is old and/or when changing refrigerant and oil types.

The subject wasn't a switch in refrigerant, but I do agree. Switching to R-134a one would not only want assurance that the high side pressure cannot exceed the design standards for R-12 but also that a compatible desiccant is used and the only way to do that is replace the dryer with one that for sure has the right desiccant.