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hjc149 on Thu April 22, 2010 10:21 AM User is offlineView users profile

I know that procedures call for replacing the accumulator/dryer whenever the a/c system is open. However, when I evacuate the system with my vacuum pump I generally let it run over night for 10 hours or so. In doing this, I wondering if this will eliminate all traces of moisture so that the accumulator can be reused.

TRB on Thu April 22, 2010 10:57 AM User is offlineView users profile

There is no need to run a vacuum pump that long. Not sure where this over night option came about but it's just not needed. Run it for 45 minutes -let it sit for 10 and then another 45 minutes. If you have got issues after doing the procedure suggested you will still have issues with a system on the pump for more than 24 hours in my opinion.

Replacing an accumulator/drier is the proper procedure in my opinion. Now if you have just opened a system to replace an o-ring or such. Normal vacuum procedures should be fine without replacing the accumulator/drier.


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hjc149 on Thu April 22, 2010 11:44 AM User is offlineView users profile

Thanks for the reply. The idea of a longer evacuation came from going thru evaporators, 3 as I recall in a couple of years, on a '69 Pontiac where I watched the shops doing the repair vacuum the system for a half hour or so. I got tired of paying for the repair and decided to learn auto a/c and took some courses. I then started to evacuate for longer periods and never lost another evap except for my Lincoln that I'm replacing now after 20 years of service. I also worked for the airlines and the mechanics told me they ran the pumps 12 hours or so. And yes I know an aircraft a/c system is much larger but so are the vacuum pumps they use. Anyway, I just though the longer evacuation period would have a greater chance of removing all moisture which when mixed with refrigerant is hell on aluminum/evaporators. I've also heard that placing dryers in a heated oven for while will restore them. Keep it in mind that I'm a DIY'er and am retired with lots of free time.

Edited: Thu April 22, 2010 at 11:48 AM by hjc149

Cussboy on Thu April 22, 2010 2:33 PM User is offline

Moisture is chemically bound to the desiccant. Heating in an oven to regenerate pellets has two large negatives:

(1) One would need to purge the accumulator during the heating process with moisture-free gas such as nitrogen

(2) The heat may weaken or destroy the "bag" that holds the desiccant, so the desiccant itself could then contaminate your AC system.

Follow TRB's advice above. Pulling a vacuum lowers the boiling point of water so it can evaporate at ambient temperatures.

NickD on Fri April 23, 2010 7:10 AM User is offline

The calcium oxide or silica gel or whatever they are using now is non-reversible. Worse part of changing an accumulator, always seem to scrape my knuckles.

Could put screws in it so you could change the bag after a good cleaning, but current method it to put it in an overcrowded landfill as well as the rest of the vehicle.

hjc149 on Fri April 23, 2010 8:04 AM User is offlineView users profile

Thanks for the input.

NickD on Fri April 23, 2010 10:11 AM User is offline

I like to take old stuff apart, slapped an old accumulator in my lath to see that bag. Shouldn't do this, the bag I saw was some kind of plastic mesh that was getting brittle and easy to break. I should have faith, but when I see stuff like this, one more thing to worry about. Still worry about flashram and how unstable it is over extreme temperature ranges. That started with OBD II, new worries.

Anyway, unlike a receiver used in TXV vehicles where there is a screen in the TXV between the receiver and the compressor through the evaporator, the accumulator feeds directly into the compressor. It's actual purpose besides storing the desiccant, is to prevent liquid refrigerant from locking up the compressor, only gas should enter the compressor.

But with that bag in their that also can seize your compressor, wouldn't risk that, just replace it, and this is far more critical in R-134a systems where moisture is more prone to occur.

tomw on Wed April 28, 2010 1:00 PM User is offlineView users profile

Nick, why do you think moisture is more prone to occur in a R134a system? I can see the criticality because of PAG/Ester liking H2O so much {more PAG than Ester from what I hear}, but not the system itself..? The 'barrier' hoses would be even less prone, no?
For the dessicant to get sucked into the compressor after a mesh failure, the refrigerant would have to be really moving. Most, if not all, accumulators have a large diameter internal tube that would force the pellets to 'climb' more than the full height of the accumulator before they would be sucked into the compressor. The FoMoCo [and likely all the rest] have a vacuum break near the top of the tube so that liquids cannot be pulled over the 'hump' and through to the compressor.
I haven't been here for years, how's things going in WI? Do they still block sales of refrigerants?


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HECAT on Wed April 28, 2010 3:02 PM User is offline

FoMoCo like this?


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ice-n-tropics on Wed April 28, 2010 3:35 PM User is offline

Good grief Nick,
They quit putting screens in automotive TXV,s over 30 years ago. It's better to let contamination circulate than to block the screen every couple of years and drive up the car warranty cost.
Bohica2xo reminded us of your role model, Kelly Johnson, just last week

Under certian conditions like going quickly from highway speeds to idle, the Acc almost fills w/ liquid refrigerant foam w/ oil. Loose Molecular Seive desiccant beads made from XH7 (or 9) could easily enter the suction hose.
Barrier (as in hose) refers to the Nylon tube near the inside of the hose which is only to reduce the emission/loss of refrigerant. Nylon actually absorbes H20, instead of blocking it. A thin layer of moisture barrier, such as EPDM, covers the outside of modern hose to reduce moisture ingress.
PAG has a hygroscopicity polar cooridinate characteristic and can take on 1% H20 if it is single end capped.
The vacuum breaker is effective to reduce liquid migration from the evap to the comp during thermal over night (climate) cycling. This reduces liquid slugging upon start up

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