How can moisture enter a closed system?

[Z2TT]

Hello,

I know the function of the receiver/drier is to filter out moisture, but why is it needed when during the Evac process the moisture is removed?

And how can moisture enter a system even if there is a leak, because the internal pressures will always be above atmospheric.

Thanks.

[powell]

Hello,

And how can moisture enter a system even if there is a leak, because the internal pressures will always be above atmospheric.

Thanks.

Moisture usually enters on the low side if there's a leak. The low side will run in a vacuum due to the loss of refrigerant.

[Z2TT]

But doesn't the system have high and low pressure switches that will stop the A/C from operating before unacceptable pressures are reached?

Thanks

[DEVIL]

But doesn't the system have high and low pressure switches that will stop the A/C from operating before unacceptable pressures are reached?

Not all systems have a filter/dryer, u can't be shore of the source of the coper that there is low amount of moisture in it, and if u do u need to vac a long period of time to be shore that all the moisture is removed from the system, and if ti's cold outside even more time to remove it, so ..... it's easier to jut add a dryer, plus electronics malfunction and might ignore a pressure switch .
Some dryers remove acidity from the oil

so ... it's easyer to be safe then sorry

[desA]

Not all systems have a filter/dryer, u can't be shore of the source of the coper that there is low amount of moisture in it, and if u do u need to vac a long period of time to be shore that all the moisture is removed from the system, and if ti's cold outside even more time to remove it, so .....

Here's a thought:
Oxygen from the copper (not 'oxygen-free' copper) + hydrogen (from oil & refrigerant breakdown) = H2O (water).

[DEVIL]

my mistake moisture from inside of the coper tube, not everybody handles correct the coper tubes in shipping and so one , not all of them are sealed and so one

[desA]

^ It's not a mistake at all. There are probably many sources of water - some there from the start, others which develop over time, in the closed system.

This would also apply to the aluminium tubes used in the automotive industry. Actually, aluminium, with its large grain sizes, is probably more porous than copper.

[DEVIL]

You mean from coper oxyd (coper rust) if develops also from not properly storying , but if u use high quality u shouldn't have this problem , and it's true water comes from many sources but if quality is your 1rst priority u shouldn't have this problem

[desA]

Copper contains a small amount of oxygen - if it not the special 'oxygen free' variety (tiny % O2).

Copper oxides (different types), interestingly-enough, can also be 'reversed' under the right conditions, which links with hydrogen in the system to form traces of water.

[Z2TT]

So it sounds like in a sealed system Aluminum can also turn into water as well when it reacts with the oil.

[desA]

So it sounds like in a sealed system Aluminum can also turn into water as well when it reacts with the oil.

The protective 'coating' for your aluminium pipes is... wait for it... aluminium oxide.

[Z2TT]

Sorry for my ignorance, but here goes.

Is the Alluminium oxide put on the inside of the pipe from the factory? Or does the aluminum oxide form with use over time, and i've heard that layer of oxide now protects further oxidation.

Thanks.

[desA]

The reason that aluminium oxide is so protective is that it forms incredibly quickly. The oxide skin 'heals' itself quickly & then limits further corrosion.

... unless

... there is an external corrosion mechanism, which breaks down the oxide layer. After that, aluminium is extremely vulnerable to surface corrosion.

[D.D.KORANNE]

At times the refrigerant also has a water content .

[Z2TT]

How does the refrigerant get this water content? I mean how is it present in the closed cylinder before its charged in the system?

Could it have entered somehow during the manufacturing process at the factory, and how?

Thanks again.

[Z2TT]

Also on another forum, A chemist replied to my question, he says

"I'm a chemist by trade, 35 years employed. There's no oxygen in "copper or alloy pipes". R-12 and R134a refrigerants themselves contain no oxygen molecules. R-12 mineral oil contains zero oxygen molecules. Ester-type oils do contain some oxygen molecules, but are pretty stable, but can absorb some water if any water is present. The drying pellets in the accumulator or drier don't have big capacity; pulling good, long vacuum before filling removes both air and water vapor, actually the high vacuum serves to lower the BOILING point of any moisture present to about ambient."

[Gary]

Evacuation does not remove all of the moisture in a system. It removes most of the moisture in a system.

[desA]

Well, the chemist is obviously not a metallurgist...

If there's no oxygen contained in copper tube, then why does 'oxygen-free copper' command a premium?

Now, tell your chemist friend this:
If hydrogen diffuses into the granular spaces & oxygen is present in those spaces, water blisters can & do occur.

This is so funny.

[paul thompson]

also bad refrigeration practice from engineers can introduce moisture into a refrig system .

[Cdubbs13]

I heard that if you pull a vacuum and then purge nitrogen through a couple times it creates a better vacuum before you evacuate, if so why is this? and when is it necessary?

[DEVIL]

The effect of vacuuming is this , in vacuum the boiling point of water is lower then 40 deg C, so closer to our environment temperature, so even the evaporation point is lower, and this makes it possible to remove moisture from a system , but this takes time, the larger the pipes the longer it takes.

Purging with nitrogen helps like this
Wen nitrogen is introduced to the system, the water particle is attaching to the dry nitrogen, so in stead of vacuuming until it gets out with the air, u just take it out, it's more faster if you have a large system

[kiwireeferman]

Moisture usually enters on the low side if there's a leak. The low side will run in a vacuum due to the loss of refrigerant.

System does not need to run on a vacuum to introduce moisture.
A leak on high (more common) or low sides can create a "venturi" effect sucking in air and moisture.

[wilko123]

Hello,

I know the function of the receiver/drier is to filter out moisture, but why is it needed when during the Evac process the moisture is removed?

And how can moisture enter a system even if there is a leak, because the internal pressures will always be above atmospheric.

Thanks.

ZSTT-Not trying to be a smart arse, but the one and only true answer to this is..the moisture comes from the filter drier. If there is a closed system with no ingress from low pressure and no bad practice to blame. Moisture can be released from the drier after long operating periods where there may be a variation in load and the temperature/pressure change causes moisture to be released. i.e dirty condensers so there is more strain and higher temps on the liquid line.

cheers WILKO

[Z2TT]

Thanks everybody,

kiwireeferman I never knew about the venturi effect drawing in moisture, as I thought as long as the pressure is higher inside than atmospheric that there is no way moisture can enter. If you can provide me with some more info that will be good, thanks for the input.

Thanks.

[Dr._Fleck]

i once worked on a mulytdeck chiller with a rotten vaporiser coil in the discharge submerged in water. It must have dragged in lots of water, tried every trick in the book to get it going again. we fitted lots of new driers, vac pump was on for days (compressor went down at this point so i fitted a new one) Faffing with Flash clock(15min on 15min off etc) and LP switch. We gave up after a couple of weeks when the pot went down again ha ha x

[John Potter]

An interesting question. Part of the answer is that not all of the water evaporates in a vacuum, and not all of the evaporated molecules make their way out of the system. Purging with dry nitrogen captures and displaces some of the pesky H20 molecules. We used to use R-12 as a 'cheap' purging agent, since the refrigerant molecules have an affinity for water molecules. Even the hermetically-sealed dryer cores will adsorb atmospheric water vapor before they are installed. The plastic caps over the ends of unitary dryers are not vapor proof, either, so the alumina may be partly saturated and may not easily give up its moisture. Some old-timers may remember that open-drive compressor rotary seals and service valve packing glands allowed "non-condensables" to migrate into compressor crankcases. Some older systems had valves at the tops of the condensers to vent off collected water. Really old-timers will remember ammonia systems with a pickle jar, filled with limewater, plumbed to the top purge valve on the receiver. Limewater turns from clear to cloudy in the presence of ammonia, so we knew when the water had been ejected when the bubbles changed color.

It seems counter-intuitive, but at the molecular level, water molecules can sneak in against higher internal pressure.

John Potter