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stardotstar on Sun March 14, 2004 6:21 PM User is offline

Year: 19891
Make: ford
Model: F150

What does descant look like?

TRB on Sun March 14, 2004 7:22 PM User is offlineView users profile

It's a small white/clear pellet.


When considering your next auto A/C purchase, please consider the site that supports you:

stardotstar on Tue March 16, 2004 1:54 PM User is offline

Thanks, so if the accumalator was bad, desicant bag broken, you would see these white pellets at the orifice tube, correct?


BTW: I'm not receiving notification of responses???

George Bray on Wed March 17, 2004 5:54 AM User is offline

If a receiver-drier or accumulator-drier, which has been in service for a few years, is placed on low heat for several hours in a dometic oven , or simply left out in the summer sun, will the crystals be dried out sufficiently for the component to be re-used? Just like re-usable silica-gel crystals for drying out hiking boots. Has anyone ever tried it?


NickD on Wed March 17, 2004 6:09 AM User is offline

This is beginning to sound like an R-134a conversion without installing an R-134a accumulator. I don't believe the desiccant used in AC systems is reversible by drying as a chemical change takes place.

stardotstar on Wed March 17, 2004 8:06 PM User is offline

I don't understand your answers now appreciate them. I asked a simple question and all I wanted was a simple serious answer in order to determine if the repair person was telling me the proper diagnosis.

It's an original R12 Ford system in a 1989 truck. No, it's not a bungled retro!

Sorry to have bothered you!

Edited: Wed March 17, 2004 at 8:07 PM by stardotstar

George Bray on Wed March 17, 2004 8:40 PM User is offline


With respect, I believe NickD may have been responding to my follow-up question. I'm sorry I gate-crashed your thread. Your initial, very straightforward question was fully answered in half a dozen words by Tim.


Thank you for your response. You know, of course, that my main goal is a R134a conversion. I will certainly fit a R134a compatible (and vertical) receiver-drier in place of the original R12 compatible (and horizontal) receiver-drier. But for the next time I have to open and evacuate the system, I just wondered if the R134a drier could be warmed-up and re-used without any performance degradation. If there's a chemical change, I assume not.


TRB on Wed March 17, 2004 8:51 PM User is offlineView users profile

Originally posted by: stardotstar
Thanks, so if the accumalator was bad, desicant bag broken, you would see these white pellets at the orifice tube, correct?


BTW: I'm not receiving notification of responses???

For some reason some members do not get the notifications. I have not had a chance to look at it since we moved over to the new server. For the cost of an accumulator $ 30.00 I sure would not want to reuse one that has oil and refrigerant ran through it!

When considering your next auto A/C purchase, please consider the site that supports you:

calairematt on Wed March 17, 2004 10:49 PM User is offlineView users profile

i wouldnt be concerned anyhow with a dessicant bag and r-134a... unless you run you vehicle in flames. moisture.. in less than measurable amounts in harmless when in contact with r134a.. it doesnt become acidic until over 500* F ... hence the small engine fire. the problem of moisture sitting on parts that may rust is a possible issue..

now an accumulator/drier replacement for "screen clogging" insurance is a great idea ... escpecially at the price of an accumulator these days.


Independent shop parts and airconditioning specialist.

NickD on Thu March 18, 2004 7:04 AM User is offline

I felt Tim answered your question quite well stardotstar, there has been hundreds if not thousands of desiccant bag ruptures reported here and the major cause was using either R-134a blends or R-134a without changing the accumulator to an R-134a unit, sorry if I assumed wrong. Would be interesting to learn why your bag ruptured, is this a high mileage truck? Nevertheless, you have a mess on your hands with possible compressor damage from pumping that grit.

The question about drawing a deep vacuum or heating up an old accumulator has been brought up many times even without a conversion, and the best I could find out is that the desiccant is not reversible. Mitch and Detroit_AC had a rather complex thread regarding even why a pressurized MVAC system absorbs moisture as opposed to say a home central unit that doesn't even have a dryer. But MVAC systems do absorb moisture, and just like the clutch pulley bearing, the accumulator has a limited life.

George Bray on Fri March 19, 2004 6:45 AM User is offline


Wow, are you saying that moisture isn't really an issue with R134a systems? The system can live quite happily with quite a bit of moisture? Therefore regular services to replace the drier and keep moisture levels low are not really justified?


Anonymous on Fri March 19, 2004 9:12 AM User is offline

I don't belive this to be true . The desiccant is tightly packed with in the bag , it filters or strains the refrigerant . It also absorbs moisture and when it does it expands there for creating a possible blockage .

? If moisture and r12 makes an acid what does moisture and 134a make .??????

aussiedevil on Fri March 19, 2004 9:14 AM User is offlineView users profile

Guess i stuffed up 3 straight posts . HA .


Anonymous on Fri March 19, 2004 1:11 PM User is offline


the desiccant can be regenerated, but not inside the bag or without using some very high temperatures. You will need to heat the desiccant up to at least 450 degrees F. and pass dry nitrogen through the desiccant to carry away the moisture released by the molecular sieve. The moisture adsorption on mol sieve is reversible. There is no chemical reaction between the moisture and the mol sieve, it is a physical adsorbtion into the micro-pores of the sieve. The bag, the o-rings and the residual oil in the accumulator are not very happy at the high temperatures it takes to regenerate the sieve. If the sieve is overheated, you can permanently change the crystalline structure of the sieve and destroy it. My company typically can regenerate used sieve about a dozen times before it seems to lose capacity.

R-134a does not readily react with moisture like R-12 does, unless you get to temperatures of molten aluminum. R-134a also holds a lot more moisture than R-12 so you will not see expansion device freeze-up unless the system is above 1000 ppm moisture. High levels of moisture are more a problem in R-134a hermetic electric motor compressors where the moisture will go after the electrical insulation components and cause electrical failures.

All that said, you still want to keep the moisture at a reasonable level to prevent the moisture from degrading the lubricant and any other moisture sensitive components in the system.

robocam on Tue August 04, 2009 12:30 PM User is offline

Why doesn't pulling a vacuum cause the moisture to leave the desiccant? And no one seems to have mentioned the main reason why moisture is bad in an R134a system. It and PAG combine to form acids that eat away your A/C!

Chick on Tue August 04, 2009 6:39 PM User is offlineView users profile

In simple terms, the discants removes moisture, and we're not talking a pint, just what is in the air, oil etc.. But like mixing water with concrete, once it's absorbs it, it's not coming out, the biggest danger is if it ruptures sending it thru the system, driers I've seen with ruptured bags (mostly R12 driers retrofitted to R134a) send a sandy coral colored mess right to the expansion valve, accumulators send it to the compressor to be ground up and plug your condenser and O tube.. Changing your drier or accumulator with a disicant rated at X7 or 9 is the proper way to go..

Email: Chick


Freedoms just another word for nothing left to lose

NickD on Wed August 05, 2009 7:44 AM User is offline

The name is desiccant,discants is a musical term describing counter melodies in a song. Desiccants remove water by absorption and since the amount of desiccant is limited, so is it's water absorption potential. PAG is a water soluble lubricant, but turns into a paste that can jam the orifice and compressor components, when R-134a was first introduced, mineral oil was not miscible with this refrigerant, so another lubricant had to be found.

Some blend manufacturers argued this point stating the shear force of the refrigerant would properly move the lubricant, but the SAE disagreed. Can only conclude the SAE is working with millions of AC systems, these blend manufactures are just trying to sell a couple of cans. But both the EPA and the SAE had to raise the acceptable moisture levels with R-134a as compared with R-12, believe it was 3 times as much, hey, this was like 16 years ago. The X-7/9 desiccant materials also had to be developed as those used in R-12 would be broken apart by some chemical reaction with the R-134a/PAG miscible solution and would be spread throughout the system causing a catastrophic failure.

Read an article on how moisture can infiltrate an R-134a system, twisted my brain as to how moisture can penetrate a much higher pressure system, some things you just have to accept. Also read an article why PAG should not be put in plastic bottles as they absorb moisture.

There is theory and practice, practice dictates whenever opening the system, the accumulator or receiver containing the desiccant that you cannot see, should be replaced if you want your system to be operable for an extended period of time. And attempts should be made to keep the interior of the system as dry as possible that may not be easy when working in a leaky shed down in Mississippi. R-12 and mineral oil did not have the problems that R-134a and PAG have with moisture absorption, so you have to be a lot more careful.

robocam on Wed August 05, 2009 12:28 PM User is offline

Interesting stuff. Brake fluid is sold in plastic bottles though.

NickD on Wed August 05, 2009 1:03 PM User is offline

Mitch and Detroit_AC were two great board members, especially when it came to theory and fluids. Mitch departed, Detroit_AC no longer shows up. Mitch as about six year my junior, it was and still is sad he is no longer with us. Here is one of his many posts..

We discussed hydraulic fluids and why so many different types, compatibility with the seals is a major factor, beside pressures and operating temperatures, but the bottom line is it's best to use what the manufacturer suggests. Since 15 years has gone by since the demise of OE equipped R-12 vehicles, the number of conversion questions has really declined. Average life of a vehicle is about 14 years, but certainly not the average life of a MVAC system, typically the first to go. Many manufacturers only warranty them for a year. Read the fine print.

Brake fluid is hygroscopic, but nearly as so as PAG nor ethanol and the materials used in automotive construction for these key areas are not corrosion resistant. Keeps us hopping.

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