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Dryers - Can Desiccant be "Dried" With Vacuum?

Barryng on Wed December 29, 2010 4:47 AM User is offline

Instead of replacing a dryer, is it possible to dry/recover the desiccant in an existing dryer by maintaining a good vacuum (500-1000 microns) for a few hours?

I have a replacement accumulator-dryer but replacing it is going to require an inordinate amount of dis-assembly of surrounding parts in a very hard to get to location. I will do it if necessary or in any doubt but I wonder if a desiccant will give up entrapped moisture by maintaining it under a good vacuum.

I realize the sack containing the desiccant might fail on an older dryer but the dryer in question was replaced when some front end damage was repaired so I am not overly concerned about its age.

NickD on Wed December 29, 2010 6:57 AM User is offline

No, not like drying out a sponge or a rag mop, a non-reversible chemical reaction takes place. Kind of like trying to unbake a cake and putting the flour, sugar, etc. back in the bag it came from.

Barryng on Thu December 30, 2010 9:23 AM User is offline

Thanks, I took your advice and replaced the dryer.

I know the the desiccant can be recovered with the application of heat so I was just thinking about a possible method of avoiding a lot of work due to the location of the dryer.

pippo on Fri December 31, 2010 8:14 AM User is offline

I thought the dessicant was silica gel? We dry that out in our lab simply by drying in a oven. Oh well, something new for me to learn......

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newton5 on Fri December 31, 2010 11:58 AM User is offlineView users profile

That brings up an interesting question pippo.
What is the desiccant in an AC dryer made of?
I doubt it's silica gel, but in all of my years turning a wrench I never thought to ask. It's not really important to know, as the dryer will normally be replaced regardless.
I do know that it makes quite a mess when the bag ruptures.

TRB on Fri December 31, 2010 12:08 PM User is offlineView users profile

It is a silica gel. But it is also mixed with refrigerant oil. Heating up a drier per the cost of replacement is just not something I'm willing to risk. You spend all this time and money on replacement parts. Then try and save a nickel on a drier.

Do it right - Do it once.


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bohica2xo on Fri December 31, 2010 4:15 PM User is offline

Well, it is a molecular sieve. Probably a mixture of silica and a zeolite, or other more tenacious material.

The issue is the high underhood temps. A dryer would not do much good if it did not hold on to the water. If the dryer regenerated while in the system, the water would wind up back in circulation. The desiccants in use today are tenacious.

The application of 130c or so while under vacuum may regenerate the dryer. May. Should ask the engineer for the dryer series.

As Tim has pointed out, the dryer is also soaked in oil. If the oil is a single end capped PAG, the released water will just wind up incorporated in the oil - degrading lubricant performance.

Usually not worth the trouble to try.


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pippo on Fri December 31, 2010 6:00 PM User is offline

Ok, now I get it. I forgot about the oil. Not worth it, plus, it just plain probably wouldnt work. Thank. (the silica gel in lab dessicators are not mixed with anything, thus, making it very easy to dry)

beware of the arrival

Cussboy on Sun January 02, 2011 6:48 PM User is offline

If you add heat to help dry out an AC drier, likely you'd weaken the desiccant sack material. That would be a huge risk to your system.

NickD on Mon January 03, 2011 7:11 AM User is offline

If they were made with a good sealing cap, could remove it and clean it and drop in a new bag. But made more like a can of tomatoes, once you open that can, its worthless, can't reuse it, so you just pitch it and load up the landfills.

Entire vehicle is getting that way, but its our responsibility to make sure WE properly recycle it. Looking at all that garbage I have to clean and haul out this morning, wasn't that way when I was growing up, and we paid good money for that worthless stuff, didn't want it in the first place, only the little stuff that was in it that sure in the hell wouldn't be that much to fill up several trashcans.

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