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Dessicant Question Pages: 12Last

emobley on Tue September 14, 2004 10:10 PM User is offline

Hi All,

I've been assembling the a/c system on my 60 Caddy and ran into a problem where I had to pull out the evaporator. Frustrated, I went to bed for the evening only to realize that I left the system open until the next evening.

Question: Is the dessicant in my drier full of moisture now? Will the vacuum remove moisture from the dessicant? Should I have my drier rebuilt again? (Can't get new ones for the 60 Caddy).


Thanks,

Ed

TRB on Tue September 14, 2004 10:23 PM User is offlineView users profile

Depends if it was raining all night. Just make sure to do a good vacuum of the system. Then let it sit for 30 minutes and pull a vacuum again. Should be good to charge after the second pull down.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com


Edited: Tue September 14, 2004 at 10:24 PM by TRB

emobley on Tue September 14, 2004 10:55 PM User is offline

No rain...I'm in California...it has been in the high 80's low 90's with 15% humidity.

We all know that heat can remove moisure from dessicant - but that is not a practical technique as it might damage the drier. What about vacuum? I've seen the posts on the topic, but didn't see a definitive answer.

Has anybody on the board taken some water logged dessicant (that has turned color) and put it in a jar under vacuum to see if the moisture can indeed be removed as indicated by the color changing back to the original? I'd be interested in the results.

Ed

emobley on Wed September 15, 2004 12:45 AM User is offline

After some Google research, I found numerous references where vacuum lowers the heat required to regenerate dessicant (both silica gel and zeolite (xh-9)). I ran across a few references of vacuum alone drying dessicant.

http://au.geocities.com/kosmonavtka2/iss/sys_sogs.html

While I wouldn't try to dry out a used drier because it also acts as a filter and would have a bunch of trash, I feel more confident that a new drier that was exposed to the air can be dried out under vacuum.

Ed

RxSteven on Wed September 15, 2004 5:47 PM User is offline

While I wouldn't try to dry out a used drier because it also acts as a filter and would have a bunch of trash, I feel more confident that a new drier that was exposed to the air can be dried out under vacuum.



Ed



I was thinking the same thing, unless the drier has been in a number of years it is still good, regardless of being open or not. Someone here replied to a similar question saying that the desiccant and water formed a irreversible chemical bond, maybe a certain desiccant? I don't think the industry would want you to know that it is unnecessary to "replace the drier whenever the system has been opened" for obvious reasons.
One drawback is the oil, from what I've read you can't remove the water from 134a compatible oils.

emobley on Thu September 16, 2004 12:41 AM User is offline

Based on my research:

A quote from: http://www.uop.com/adsorbents/7010.html:

"Zeolite molecular sieves are crystalline structures that, on a molecular scale, are not unlike sponges. They have a solid framework, defined by large internal cavities where molecules can be adsorbed. "

It's my understanding that XH-9 is a zeolite dessicant. I didn't run across any zeolite dessicants that couldn't be regenerated by heat. Therefore, I doubt that there is any type of irreversible chemical reaction.

One zeolite dessicant required a much lower temperature if you regenerated it at 26 inches of vacuum (something like 200 degrees versus 350). Well, that's not a very strong vacuum. Therefore, I would imagine that 29.5 inches of vacuum would lower the temperature for regeneration even further - perhaps a temperature that could be achieved by warming up the car.

As far as exposure to oil is concerned, I'm not sure what sort of an effect it would have on dessicant regeneration.

Ed

emobley on Thu September 16, 2004 12:55 AM User is offline

One other thing:

I get the impression that the practice of replacing the drier whenever the system is opened has more to do with the fact that a system is usually opened because something has gone wrong. A compressor failure would fill the drier full of trash. A retrofit to 134a would require a compatible dessicant. I think you get the idea.

Ed

tony1963 on Thu September 16, 2004 3:45 AM User is offline

Drier drier pants on fire!

-------------------------
Grove Automotive Group, Inc.

An Alabama Corporation

Anonymous on Thu September 16, 2004 10:06 PM User is offline

Quote
Originally posted by: tony1963
Drier drier pants on fire!

Now that is funny!

Ed, no, I've had the idea, in my Haynes ac manual it says:

Replace the receiver-drier:
a) When a major leak allows ambient air and moisture to enter the system.
b) When the system is opened for a lengthy period of time without being capped.
c) When the sight glass turns cloudy.(desiccant has broken down)
d) When the expansion valve is replaced.(valve malfunction usually caused by moisture in the system)
e) When the STV, POA, EPR, or exp. valve is replaced. (each of these components usually malfunctions
when moisture enters the system.)

There are 2 more reasons, they are clogs and restrictions, but you get the idea.
I think compressor failure or conversion would be obvious reasons to change it out

Although I am a novice, I have to give kudos to TRB for his above answer.














RxSteven on Thu September 16, 2004 10:17 PM User is offline

That was me, I wanted credit for my post, so one day, I too can be a senior member!

Anonymous on Thu September 16, 2004 10:22 PM User is offline

Just make posts like Tony does. That'll get your numbers up.

RxSteven on Thu September 16, 2004 10:32 PM User is offline

Just like Tony?

He is off the hook!

emobley on Fri September 17, 2004 1:30 AM User is offline

We'll just let folks like Tony have fun with their juvenile remarks.

I would be very interested if somebody has additional information as to whether or not dessicants can be regenerated with vacuum alone.


Thanks,

Ed

TXAB on Fri September 17, 2004 10:24 AM User is offline

A quick search of the site turned up these previous posts concerning drying dessicants.

Post 1

Post 2

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"Don't get stuck on stupid!"
---- Lt. Gen. Russel Honore

emobley on Fri September 17, 2004 12:09 PM User is offline

Yes, I read those posts - but thanks for pointing them out for the other readers. I agree that it is not worth trying to save a used drier.

Until I hear differently, I get the impression that a deep vacuum would remove what small amount of moisture would enter a NEW drier either from extended storage or, in my case, where I left the system open over night.

Thanks,

Ed

TRB on Fri September 17, 2004 12:12 PM User is offlineView users profile

I would not try reusing a used drier! But in your case it was a new item that was just left open for a short time.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

calairematt on Fri September 17, 2004 10:56 PM User is offlineView users profile

at sea level under 29.9" of vacuum it take one hour to boil approxamately one drop of water. I agree with tim that if you get a really good vacuum and hold it and then hit again with the pump you should be fine. i did some research when i was looking for desicant sacks for late model toyota/lexus that are drop ins next to the/attached to the condenser and Stanhope industries would probably be the people to talk to ... unfortunately i dont have thier info anymore..... and they say that desicant when saturated with moisture cannot be dried out and that in 7% humidity the average drier is saturated in less than an hour.

Just my two cents ... i may need change.


-------------------------
Matt

Independent shop parts and airconditioning specialist.

bohica2xo on Sat September 18, 2004 3:23 AM User is offline

Certainly desiccants can be regenerated with vaccuum - as long as you have enough time and vaccuum.....

Desiccants are regenerated commercially all the time. Vaccuum simply lowers the boiling point of water. If you can pull down into the 400~1000 micron range, and hold it there - you can regenerate desiccant at 70f quite well.

For a dryer that was left open, this is perfectly acceptable. I have received more than one dryer with one of it's seals rolling around loose in the box. When you can hold the 400~1000 micron vaccuum for 30 minutes without change, (with the pump isolated) there is simply no more water to be removed.

In addition to all of the other VERY good reasons for discarding a used drier already stated, consider this - When acids form, they wind up trapped with the water in the desiccant. So no matter what you do, you may have acid in a used drier.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Sat September 18, 2004 8:27 AM User is offline

This is certainly a controversial subject as to whether drawing a deep vacuum can restore the action of a desiccant or not. There are many different types of desiccant used and the first question is, exactly what is buried deep inside that can we call either a receiver or an accumulator.

One thing we know by experience is that the MOLSIV desiccants such as XH-7/9/11 must be used in an R-12 conversion, but exactly what are the chemical properties of these desiccants? In general, desiccants may be more mechanical in nature trapping moisture in pores like a sponge where others may be chemical in nature where the moisture absorption causes a non-reversible chemical change. The manufacturers of these products don't seem to want to say exactly what these properties are.

Another rather mysterious subject is how does moisture get into a highly pressurized MVAC system thus requiring practically since day one of all MVAC systems to employ some type of dryer in the system. But apparently it does or otherwise some type of desiccant would not be added as the stockholders could use that money. And if moisture does penetrate the system, how long does it take for sufficient moisture that can cause significant damage? Perhaps by changing the oil and refrigerant every couple of years or so like brake fluid is all that is needed after drawing a deep vacuum to dry the system out.

Yet another question is, what is the moisture capacity of the desiccant that is buried in that can, would be nice to learn some figures as to how much moisture actually can enter the system, what time frame are we talking about, the effects of the ambient of moisture, this is assuming the initial system is bone dry, leading to the life expectancy of the desiccant. Never read anything in any shop manual that states the accumulator or receiver should be changed every X miles or years for that matter.

Yet another factor with the damaging effects of moisture is highly dependent on the materials used in the AC system, apparently aluminum is on the bottom of the list as it is far more porous than other materials such as cast iron, brass, or copper. Aluminum seems to be the standard today, but one can't really complain too much about this sub-standard material as the cost of an AC system in say a 1957 Chevy practically doubled the cost of the vehicle where today, the cost of an AC system is only a small fraction of the cost.

But in reading the small print on some new vehicle warranties, while the drivetrain may be warranted say for 100K miles, the AC system is only warranted for 12 months.

We are told by the desiccant manufacturers that we need some type of dryer as the moisture will lead to aluminum corrosion and I gather in very extreme cases can even freeze up the small orifice tube leading to compressor failure problems due to lack of lubrication. But in general, most say their desiccant can only absorb about 20% of their weight in moisture. Again all these statements are qualitative in nature but certainly not quantitative, it remains to be a mystery.

Perhaps DetriotAC can share some insight on the question as to whether the common desiccants used in MVAC applications can be somewhat restored by drawing a deep vacuum. And what about the expected life of a system? Does the RH of the environment say as opposed to a Florida based vehicle to a one that is in the dry dessert make a difference?

In spending about two hours on the net searching out this subject, I have more questions than answers.

Karl Hofmann on Sat September 18, 2004 8:47 AM User is offlineView users profile

I am yet to see a system to corrode from the inside out, the alloy pipes always corrode from the outside in helped by the strategic positioning of steel support brackets in areas that will be subject to road spray in the Winter, Ford have even managed to cut things so fine that their acs were failing within warranty and killing the Sanden SD7V16 compressor. Makes you wonder why they even bothered to go to all of the expense of using a dessicant, apart from the bizare prices that they charge for a new drier.

-------------------------
Never knock on deaths door... Ring the doorbell and run away, death really hates that!

NickD on Sat September 18, 2004 8:59 AM User is offline

GMtech made the same comment regarding GM evaporator failures, all those he had seen rotted out from the outside. Maybe that desiccant is needed to remove the acid rain that flows into the evaporator.

Karl Hofmann on Sat September 18, 2004 9:11 AM User is offlineView users profile

Quote
Originally posted by: NickD
GMtech made the same comment regarding GM evaporator failures, all those he had seen rotted out from the outside. Maybe that desiccant is needed to remove the acid rain that flows into the evaporator.

LOL or maybe a better quality of aluminium alloy or the appliance of school boy physics regarding dissimilar metals

-------------------------
Never knock on deaths door... Ring the doorbell and run away, death really hates that!

DNT on Sat September 18, 2004 11:07 AM User is offlineView users profile

Next time I am at the refrigeration supply house, I am going to check and see if they have a sporlan inline filter with the moisture indicator sight glass and compatible with r134a and capable of being installed in a 3 or 4 ton system. This is standard practice on traditional residential and commercial units why can't we use it for MVAC? It would give a real world look at what is going on inside the system regarding moisture content. Of course they may be prohibitively expensive but the inline sporlan filters that I bought for my recovery machine where only six bucks a piece. Just a thought has anybody out there tried this.

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Anyone who gives up freedom for the sake of safety, deserves neither freedom nor safety!

emobley on Sat September 18, 2004 11:49 AM User is offline

Thanks all for some really thoughtful replies.....

Quote
One thing we know by experience is that the MOLSIV desiccants such as XH-7/9/11 must be used in an R-12 conversion, but exactly what are the chemical properties of these desiccants? In general, desiccants may be more mechanical in nature trapping moisture in pores like a sponge where others may be chemical in nature where the moisture absorption causes a non-reversible chemical change. The manufacturers of these products don't seem to want to say exactly what these properties are.

That's what I'm lead to believe. I've even heard the words "capillary action" to describe how dessicants work. It seems like the manufacturers can control the size of these pores which controls the types of chemicals that the dessicant will absorb. Perhaps the differences with dessicant compatibility have to do with the size of these pores (i.e. will soak up water but not oil or refrigerant)? I'm sure people have Phd's in this subject.

Quote
I have received more than one dryer with one of it's seals rolling around loose in the box.

Many of the driers I've seen come from the factory with dust caps - they certainly are not air tight. This makes me wonder how much moisture they are absorbing just sitting on the shelf (especially in a humid environment).

Quote
Another rather mysterious subject is how does moisture get into a highly pressurized MVAC system thus requiring practically since day one of all MVAC systems to employ some type of dryer in the system. But apparently it does or otherwise some type of desiccant would not be added as the stockholders could use that money. And if moisture does penetrate the system, how long does it take for sufficient moisture that can cause significant damage?

I believe it has something to do with osmosis: the movement of water molecules from an area of high concentration to an area of low concentration. I don't know if water enters through small leaks or the hoses - but I understand that it still gets in. Perhaps the barrier type hoses are more resistant to osmosis?

Should we be replacing our driers at certain intervals? Great question.....

Quote
Next time I am at the refrigeration supply house, I am going to check and see if they have a sporlan inline filter with the moisture indicator

Please let us know what you find out. Something like a moisture indicator would let us know if/when we should replace the drier.

Quote
In spending about two hours on the net searching out this subject, I have more questions than answers.

Ditto....


Thanks,

Ed

Karl Hofmann on Sat September 18, 2004 4:13 PM User is offlineView users profile

I think that you will find that most bus aircon manufacturers and transport fridge manufacturers use refrigeration industry standard components, and copper tubing. It always amazes me how a filter drier for a Plaxton 42 seater coach can cost £10 and an accumulator for a Jeep Diesel can cost over £130

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Never knock on deaths door... Ring the doorbell and run away, death really hates that!

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