ReplyMicrons for microns sake are overrated........
Professional Member
Out of curiosity when pulling a vaccum will you guys always pull until 500 microns? I've worked with many guys who get 800 even 900 and let it rip. I'm just trying to establish a sound method I've always pulled low but sometime that thing will just run for hours before it gets to the 5 range. I've seen some of the setups which are cool yet some are pricy lol so I want to eventually save for one on the forum. Also do you guys use a set of gauges just for vaccum that you trust? I trust all my tools but I've known guys who say they use a set just for vaccum even if it doesn't have the 3/8 line. Is that odd? Waste of money?
Professional Member
Microns for microns sake are overrated........
Professional Member
I pull to 300 microns on a new install and 500 on a system I've opened.
I do not pull through my gauges a d have dedicated 3/8" vacuum hoses.
Professional Member
And why would you go through the trouble to set all that stuff if you are not going to pull a proper evacuation anyway ?
I guess I already know the answers to that one and they are all sad but true.
Professional Member
There's the supertech side and the practical side to this procedure. Supertech will want to do what they were taught was correct and Mr. Bucks will want to do what's necessary.
Any air left in the system will probably spend it's life stranded in the top of the condenser. Any moisture will probably find it's way to the drier. So in some regards both mind sets end up with the same results.
What's correct or what's necessary. There is often a change of mind over time where the guy starting out will be by the book and the ol timer might not so much. As it is in the field you can never git everything out. Close but not all.
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Professional Member
Agree, the purpose of evacuation is the removal of moisture, the vacuum rise over time is the best indicator of residual moisture in a system not the level of Micron acheived. Too big a pump on too small a system can freeze residual moisture allowing a low micron vacuum level to be acheived. Determing the point of equilibrium assists determining if residual moisture (or a leak) is presentOriginally Posted by klove
Necessity is the mother of invention
Professional Member*
I use the vacuum setup in the picture below. I usually try and do a "triple evac" with nitrogen. I will let the vacuum pump run until the micron gauge shows a low number, then I valve it off by closing the valves on the core removal tools, and the micron gauge will slowly rise and level out.
Generally, I stuck with this rule of thumb.
If I'm in a hurry (ie walk-in freezer at 40, food starting to thaw), I will pull a vacuum as long as feasible, then I valve it off and if it levels out around 1000 microns after couple minutes I will call it good.
If I'm not in a hurry, I will valve it off, and if it holds below 1000 microns for ten minutes I call it good.
If its a new install of a new system, I will valve it off and if it holds around 500 microns or less for ten minutes I call it good.
Professional Member
You can always throttle down an oversized pump. Just partially close off the valve you use to isolate the pump from the system.
Your best friend when it comes to removing moisture is heat. But don't use a torch due to the fire hazard. Use a hair dryer or halogen worklamp to heat up cool parts of the system. Activate crankcase heaters if the system has them, but disconnect the compressor first.
BTW, for those who frequently work with refrigeration, it might be a good idea to build an "emergency cooling cart" (water cooled condensing unit plus evaporator coil or glycol exchanger mounted on wheels) in order to buy some time.
Professional Member
Cool mike19 so what exactly is your setup what kinds of hoses? I assume when your ready to charge you just valve off at the core removal tool? Nihao what do you mean throttle down a pump? Why would you want to do that?
Professional Member*
I made a setup just like slctech has in this thread. http://hvac-talk.com/vbb/showthread....ac-pump-set-up
When I'm ready to charge I unhook the hoses from the core removal tools and hook my gauge manifold up, then pull a quick vacuum on that.
It really does help to pull a vacuum faster. You can get the big black 1/2" hoses either the appion brand, or united sells the nrp brand. They have a 1/2" connection on one end and a 1/4" connection on the other. You can use a couple of the big hoses with a 1/2" flare tee, and a short hose or some other fittings to hook it to your vacuum pump. That works just as good, that's what I did before I made the setup I have now.
Professional Member
To solve the "moisture freezing" problem.
Professional Member*
IF there is enough standing water to freeze before it evaporates (not likely) the resulting ice will be sublimating to vapor causing your micron level to rise, so you would still "see" the moisture in the system. A few small droplets of water will evaporate long before they freeze no matter how fast you pull down.
The only time you might have enough water to freeze would be a water cooled coil leak that flooded the refrigerant system, or someone deliberately poured a cup of water into the system.
Professional Member
You can also use the gas ballast for this purpose.
It'll prevent the pump from pulling a deep vacuum and freezing any moisture present.
If you've got enough moisture to freeze, you've got bigger fish to fry, IMO, though.
I'm quite curious about your "cooling cart" idea. I've done refrigeration for many years and have never seen or heard of anything like this.
Professional Member
True providing you have sufficient heat energy for the phase change to occur and allow sufficient time.
[QUOTE A few small droplets of water will evaporate long before they freeze no matter how fast you pull down.QUOTE]
This dependant purely dependant on how quickly the vapour pressure is acheived - you might be surprised when you watch this
http://www.youtube.com/watch?v=azK_B8ekmPE
[QUOTE The only time you might have enough water to freeze would be a water cooled coil leak that flooded the refrigerant system, or someone deliberately poured a cup of water into the system.[/QUOTE]
Common when dealing with a tube related failues with chillers.
Necessity is the mother of invention
Professional Member*
Seems to me if you are reaching 200 microns in 5 minutes that would be fast enough to freeze moisture. Still since 72 I don't think I have ever had that problem. I am using the JB 10 CFM pump, and usually open the gas ballast for a few minutes.
Professional Member*
I thought the lower the vacuum, it boiled the moisture out of system. How would it freeze it?
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Professional Member*
I've seen in a service school where 1 drop of water froze in a test tube in 10 m minutes and never did evaporate in 3 hours.
Professional Member*
Interesting. Was it valved off? And how fast was the micron level rising?
Professional Member*
If I remember correctly it was a 5 cfm pump, it ran the whole time, there were three test tubes used, 1 had 10cc POE oil, 1 had 10cc mineral oil, the third was empty, all three got 1 drop of water. The water only turned to ice and just sat there, there was no noticeable change in the two tubes with oil either. The point of the test was to show that vacuum alone will not remove water, especially with POE oil.
Regular Guest
We do a demonstration using the Debris Tube on the Tez8, where the moisture boils, then freezes, then sublimates. Inside of a thermally isolated tube or glass, the moisture will sit there frozen, and take some time to sublimate.
However, the thermal mass of the components in an AC system prevent freezing in most scenarios, so the water evaporates before there is sufficient vacuum to trigger the freezing process. What remains sublimates pretty quickly... this is even true in cases where a water cooled coil leaked and is flooded.
For science, we decided to try and cause water to freeze in a system (rather than an isolated glass jar or plastic tube), and we found that an ounce of water, when trapped in a 1"-diameter low point, would mostly boil off, and the remaining moisture would sublimate quite rapidly. With this system dry, the evacuation took 5 minutes. With the ounce of water and sublimation delay, the evacuation took 15 minutes (no other heat applied).
In short, freezing water in a system is something that happens in a lab more than in the field, and the real delay factor here is saturating the vacuum pump oil with water. Changing the oil when it gets saturated keeps the pump chugging along, and greater pump capacity is actually useful in keeping the sublimation process fast, so the sublimation process doesn't impact the evacuation time much.
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