Evacuating refrigerator compressor

[JKMilligan]

When trying to clean a system of any moisture or contaminates, is there a general rule of thumb on how long you should keep it under vacuum?

[a64pilot]

Many vacuum systems aren’t capable of going as deep as you need or want to.
I’d leave it running overnight, it hurts nothing at all if left on longer than needed.

[dkenny64]

depends on the level of vacuum your pump is pulling..
28"
what's the temperature? this determines the boiling point of water..that you
are trying to remove..longer is better.

the pump i've used pulls 29.995 inches..its a special high vacuum pump I bought for another purpose..but for AC systems its wonderful. and doesn't long to dry one out.

my uncle made a vacuum pump out of an old compressor..it takes about 30 minutes on a car system at 80F.. does the job and cheap.

just my 2 cents
-dkenny64

[s/v Jedi]

If you have a decent pump and not too long refrigerant lines it doesn't take long. What really helps is to run a heat gun along all the plumbing, dryers, evaporators, condensers etc. My compressor has a little dryer filter bulb in the return line. When I hit that under vacuum I immediately hear the pump evacuate more moisture. Same for evaporator plate. I keep doing that until it all stays quiet, then quickly tire of the pump noise and it's heat buildup.

I have learned any decent job, incl. installing brand new pre-filled systems, last about 5 years before requiring service. It can be just an O-ring but when I evacuated my Frigoboat system after 5 years while replacing O-rings, I clearly heard moisture come out. The system is now 14 years old and still going strong. Two of the three keel coolers have failed but I still keep two of them (all I need right now) going with an air cooled condenser on hand in case one really dies

[OzePete]

Good advice here but I might just add that you should replace the dryer with a proper FILTER -dryer type 032 or 052.
Evacuate from both high and low sides, then add enough refrigerant to balance out a pressure just above zero PSIG. Remove the high side hose, run the unit and slowly top up via the suction but not allowing the suction to go above 15PSIG (low side).
Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[Richard Kollmann]

Twenty nine inches of vacuum may have worked with mineral oil refrigerants but it will not dehydrate moisture from Ester oil and 134a. It will require an additional 20,000 microns of vacuum. Super Dehydration down to less than 500 microns is necessary separate moisture from new oil. It is true that a two stage pump with complete refrigerant system warm can reach 500 or less in 12 hours.

It pays to be alert for misinformed information on the web. If you want to confirm technical advice Google search, Example Question ( How to remove moisture from Ester and 134a refrigerant)

[skipmac]

Originally Posted by Richard Kollmann

Twenty nine inches of vacuum may have worked with mineral oil refrigerants but it will not dehydrate moisture from Ester oil and 134a. It will require an additional 20,000 microns of vacuum. Super Dehydration down to less than 500 microns is necessary separate moisture from new oil. It is true that a two stage pump with complete refrigerant system warm can reach 500 or less in 12 hours.

It pays to be alert for misinformed information on the web. If you want to confirm technical advice Google search, Example Question ( How to remove moisture from Ester and 134a refrigerant)

Hi Richard,

As always very interesting and informative. I did indeed google as you suggested and started doing further research on this. Watched one video on youtube where a tech added water to ester oil (which made it very obviously cloudy) in a clear jar then put it under a vacuum. You could see the water coming out of the oil and see the oil gradually clear but after a couple of hours was still quite cloudy and for as long as he ran the test it never completely cleared up. However the tech did not say what level of vacuum he was pulling so not as informative as I would like.

First question, with sufficient time and level of vacuum will the ester oil completely dry?

My system is fairly new and so far so good but I would like to be prepared for if or when I do need to vacuum and recharge. So any recommendation on a reasonably priced vacuum pump that would do the job for a consumer IE not heavy duty and spec'd for daily, commercial use.

On a related issue, if I do have to dry and recharge my system somewhere down the road would it make sense to add a larger filter/drier to the system? I have a Frigoboat BD50 system and I think it does have a very small drier in line.

[Richard Kollmann]

Originally Posted by skipmac

Hi Richard,

As always very interesting and informative. I did indeed google as you suggested and started doing further research on this. Watched one video on youtube where a tech added water to ester oil (which made it very obviously cloudy) in a clear jar then put it under a vacuum. You could see the water coming out of the oil and see the oil gradually clear but after a couple of hours was still quite cloudy and for as long as he ran the test it never completely cleared up. However the tech did not say what level of vacuum he was pulling so not as informative as I would like.

First question, with sufficient time and level of vacuum will the ester oil completely dry?

My system is fairly new and so far so good but I would like to be prepared for if or when I do need to vacuum and recharge. So any recommendation on a reasonably priced vacuum pump that would do the job for a consumer IE not heavy duty and spec'd for daily, commercial use.

On a related issue, if I do have to dry and recharge my system somewhere down the road would it make sense to add a larger filter/drier to the system? I have a Frigoboat BD50 system and I think it does have a very small drier in line.

Here is the Short story when mineral oil and moisture droplets mixed completely the oil would release moisture at a vacuum of 30 inches with an ambient temperature above 60 degrees F.. Once droplet was released it changed to steam vapor. Vacuum pump then removes moisture as a gas vapor.

New refrigerant oils POE and PAG absorb droplets of moisture so tightly it can not be easily removed from these oils. The current way to remove moisture I call Super Dehydration, Warm up complete refrigeration system including evaporator and space refrigerated to 100 degree F and keeping temperature there while evacuating for 4 hours after reaching 500 micron pressure.

If using a micron gauge and my procedure when gauge reads 200 micron for one hour or vacuum pump was run more than 12 hours you can be reasonable sure moisture is gone.

A small vacuum pump is all you need for a small 12 volt system but any pump used must be ratted as low as 50 micron. I would not purchase an air operated vacuum pump. If your system contains less than one pound of refrigerant even the smallest two stage pump will do what you need and it will also do much larger systems it just takes longer.

One Point I always like to make is do not ever think you can use a vacuum pump when looking for a refrigerant leak. There are two reasons why You only removing atmospheric pressure of 14.7 pounds and if there is a leak you are only drawing in more moist air. One more thing you should never tamper with refrigerant unless two non destructive tests indicate and confirm there is a refrigerant or refrigerant flow problem.

If a system is set up for simple quick filter dryer changes with Flare nuts then change it. Only job shop refrigeration without quality control and DIY systems need larger filters. Remember Super Dehydration also removes moisture in filter dryer.

[CGirvan]

I've a few questions about this process,

When people talk about holding a vacuum overnight, is that with the vacuum pump running continuously or can you draw the system down then close the valves and shut off the pump?

I've heard mention of doing a triple nitrogen purge (not sure if that's the proper term) How does this compare to a proper evacuation for getting the moisture out?

I've also heard people mention that it was somehow possible to collect all the refrigerant into a large filter drier so work could be done on the system without losing all the refrigerant. Is this possible?
Secondary to this, Richard, you mentioned changing the small tube type filter/driers if fitted with flare nuts, can this be done without losing the refrigerant?

Thanks for your comments.
Colin

[Richard Kollmann]

Originally Posted by CGirvan

I've a few questions about this process,

When people talk about holding a vacuum overnight, is that with the vacuum pump running continuously or can you draw the system down then close the valves and shut off the pump?

I've heard mention of doing a triple nitrogen purge (not sure if that's the proper term) How does this compare to a proper evacuation for getting the moisture out?

I've also heard people mention that it was somehow possible to collect all the refrigerant into a large filter drier so work could be done on the system without losing all the refrigerant. Is this possible?
Secondary to this, Richard, you mentioned changing the small tube type filter/driers if fitted with flare nuts, can this be done without losing the refrigerant?


Thanks for your comments.
Colin

Colin, You ask good questions.

Holding a vacuum over time can not be done without compressor running because as moisture boils and changes to steam vapor reducing Dehydration vacuum. The process when compressor is running is to reach the boiling point of all moisture locked up in oil.

Triple vacuuming with refrigerant or better yet Dry Nitrogen was used 25 years ago when vacuum pumps were not in a mechanics tool box. I even sold complete refrigeration kits with instructions to triple evacuate using three small cans of Freon R12. As to triple vacuuming system containing POE Ester oil with Dry Nitrogen it will defiantly remove gas vapor and moisture locked in refrigerant but probably not small droplets locked in POE oil. The belief that if small amounts of moisture that will not freeze and restrict refrigerant flow is not harmful is wrong. Refrigerant plus oil and moisture causes damaging acid sludge.

Many refrigeration system designs include isolation valves on each side of filter dryer allowing filter changes without loss of much refrigerant. Those systems with TXV and refrigerant receiver can have a King three way valve at receiver that normally allows all refrigerant to be stored in receiver for a short time.

The size of a filter dryer and how it will be attached to a line is determined by the risk factor of future replacements. A clean quality controlled system assembly will only need a small filter to collect small amounts of moisture and small dust left in your system. If it is a DIY system or a system from a Job shop a larger filter dryer is smart engineering.

Colin, I do no know who manufactures your refrigeration unit but only a few system builders will expose you to the problems you are concerned with.

[a64pilot]

Only systems I have worked on that you could pull refrigerant down into the receiver were house cooling systems.
I would think this would be very unusual for small systems like our boat fridges?

Also if you pull a vacuum down, close the valves and turn off the pump, watch the gauges. A loss of vacuum indicates usually a leak although it could indicate a lot of moisture.
Of course not being able to pull a hard vacuum indicates a pretty big leak.

[Richard Kollmann]

Originally Posted by a64pilot

Only systems I have worked on that you could pull refrigerant down into the receiver were house cooling systems.
I would think this would be very unusual for small systems like our boat fridges?

Also if you pull a vacuum down, close the valves and turn off the pump, watch the gauges. A loss of vacuum indicates usually a leak although it could indicate a lot of moisture.
Of course not being able to pull a hard vacuum indicates a pretty big leak.

Most boat icebox conversion refrigeration systems containing more than a pound of refrigerant have a way trap and store refrigerant.

Attempts to test for a leak with a vacuum pump is not only a waste of time. If there is a leak the complete system may be contaminated.

[grahamb]

Using a vacuum pump may be likened to wishing to remove all moisture from a container that you want to use for diesel fuel, by placing the container over a heat source and keeping that heat source there until all moisture is evaporated out/boiled out. But because the inside of that container cannot be seen the best way to know all moisture is gone is to keep the heat source there for a long period. Rather like having a vacuum pump run for a long period.










But a refrigeration system contains oil, as does the high vacuum pump itself, and the oil contains moisture, which will slowly boil out/evaporate over a long period, hence the need to have a true vacuum pump run for a long time. After ,say,an overnight run, isolate the vacuum pump from the system by use of the refrigeration service manifold ,turn off the pump, and watch the vacuum reading on the service valve for any rise. If a slight rise and then stops whilst gauge still shows in vacuum and holds, it is fine. A continuous rise means there is moisture present and the pump should be restarted.
There are specialist instruments available from refrigeration parts wholesalers that provide a vacuum reading in microns. The lower the better. But the reading must hold.


It is interesting that temperatures as low as -70 deg.F have been observed at the point in the refrigeration system where the compressed liquid refrigerant '
'flashes off to become a saturated vapour where it enters the evaporator/eutectic plate (typically at the TXV...thermostatic expansion valve/or the capillary tube). So any moisture will instantly turn to ice ,and may well block/impede refrigerant flow, giving insufficient cooling/intermittent cooling.


Always replace the drier because moisture is/may be trapped there.

[a64pilot]

Originally Posted by Richard Kollmann

.



Attempts to test for a leak with a vacuum pump is not only a waste of time. If there is a leak the complete system may be contaminated.

Understood, that is why after achieving a vacuum you close valves and turn the pump off and watch vacuum gauge, cause if there is a tiny leak, you need to stop and fix it, prior to pulling in all that warm moist ocean air.

[Richard Kollmann]

Originally Posted by a64pilot

Understood, that is why after achieving a vacuum you close valves and turn the pump off and watch vacuum gauge, cause if there is a tiny leak, you need to stop and fix it, prior to pulling in all that warm moist ocean air.

If there is a rise in suction pressure when stopping pump it may be just more moisture boiling off. Another problem do you think 14.7 psi of vacuum will detect a 110 psi high pressure leak of one ounce per year. With the proper leak test breaking down surface tension with a mixture of soap and water brush method has proven to find very small leaks.