Tag: vacuum

Testo 557 vacuum gauge and Appion core removal tools shown

I’ve had a change of heart.

Back in the early 2000’s during the big construction boom I did a lot of system startups on residential units for a large company I worked for.

When installers were running the linesets prior to startup they weren’t always very careful to keep them clean and dry and many times we would end up with a restriction in the piston or TXV.

These new residential systems come with a precharged with refrigerant in the condenser. So after my vacuum was complete I would “release” the charge by slowly opening the liquid line service and watching to see if my suction pressure would steadily rise.

I did this so if there was anything in the liquid line it would hit the screen or drier before the metering device instead of possibly running the other way and clogging the TXV or orifice.

Many times I would know that there was a restriction before I even started the system because I got used to watching that suction needle rise. While I did this for a good reason that reason is in the past.

When we install systems we take great care to make sure the lineset stays clean and dry and we flow nitrogen while brazing with the line drier installed near the indoor coil.

It’s a new day and I’m giving up my old sins.


So now I must admit… the better way to do it is to slowly open the SUCTION valve first. This prevents oil loss out of the compressor into the discharge line and out of the liquid line.

It is not likely that you will lose enough compressor oil to cause any damage by opening the liquid line slowly, but any oil the compressor does lose has a long journey before it gets back to the compressor. The other issue is that oil loss in those first few moments in the life of a new system can have long lasting effects on the operation and longevity of that compressor.

Have you ever taken a liquid line hose off after a new system install and gotten oil all over?

The reason for that is often due to opening the liquid line first and the compressor losing oil to the discharge line and then to the liquid line.

When you open the suction side slowly first and oil loss from the compressor will enter the suction line. Once the compressor begins running no it will pull that oil back into the compressor.


When doing it this way you would attach your micron gauge to the liquid line core remover side port with the schrader in place in the side port. Once you completed your vacuum and proved you had no leaks or moisture by valving  off the VCT’s and watching your decay rate. You would then attach your gauge manifold and slowly crack the suction side until you see a few psi on the liquid side. Now remove the vacuum gauge to ensure it is not damaged by the system pressure.

Most micron gauges can handle some pressure, for example the Testo 552 can handle up to 72 PSIG(4.96 bar) and many can handle 400 psi(27.57 bar) or more. it never hurts to remove that expensive and sensitive micron gauge before you expose the sensor to high pressure, but never remove it BEFORE the system is under positive pressure or you will lose the entire vacuum.

You would then purge your manifold hoses and fully open the suction valve and then the liquid line valve.

When charging a system that has no charge (not running) weigh refrigerant into the liquid line first until both sides equalize in pressure to ensure that you are not introducing liquid refrigerant right into the compressor crankcase.

Also keep in mind that running the crankcase heater once the charge has been released and before the system is started is also a good practice to prevent flooded start on the compressor.

— Bryan

As a technician gains skill they will learn that regularly testing your tools is a huge part of success. It isn’t long in the field before techs find out that just because a meter or gauge gives a particular reading it doesn’t ALWAYS mean it is correct. Vacuum is one of these areas.

Everything in an air conditioning and refrigeration system leaks to some extent, our job isn’t to eliminate all leaks, our job is is to reduce the leakage rate to as low as possible. When using a sensitive micron gauge we find that isolating an assembly and checking the “decay” or standing leak rate is a great way to test and ensure that a system has minimal leaks and moisture. The challenge is that all of the connections in your rig leak and even the vacuum gauge itself leaks.

Some techs attempt to test the leak rate on micron gauge by connecting it to a core tool and then straight to the pump, evacuating the gauge down to very low level and then valving off. If you do this, you will find that every commercially available vacuum (micron) gauge shoots up pretty quickly. This is because the VOLUME of the gauge and coupler are so low that ANY leakage whatsoever has an enormous effect.

In this video Ulises Palacios shows us how to use an an empty recovery tank to better test the leak rate of a vacuum gauge rig.

It is certainly important to test all of your vacuum rig components, just remember that volume makes a huge difference when decay (standing vacuum) leak testing.

— Bryan

When evacuating, the FASTEST way is to use two large diameter hoses connected to two core removal tools and the cores removed. These hoses are then connected to the pump using a tee or evacuation “tree”.

However, when you only have one large hose another acceptable method is to connect the large hose to the suction side and the vacuum gauge to the liquid side alone.

Brad Hicks from HVAC in SC made a nice little video showing how he does this with just one hose. He uses a core tool with the vacuum gauge on the liquid line to ensure that there aren’t and issues with depressing the core, which happens often with certain cores and gauge couplers. The other reason is so that he can valve off the vacuum gauge when he releases the charge or charges the unit to prevent refrigerant and oil from potentially entering his vacuum gauge.

The disadvantage of this setup is that the vacuum must all pull through the metering device which can add time to the process. In the case of a “hard shut off” TXV this method may not work.

Transcript

Well guys here’s another 60-second tech tip video. This one’s going to be on single hose evacuation setups. I get tons of questions on the subject so hopefully, this will clear things up a little bit. It’s very very simple, all I have is two valve core removers here both ports liquid and suction have been removed. On the liquid side, I’ll have my micron gauge. In this case the BluVac Pro and on the suction side I have my Appion hose. This is a six foot(1.82 meters), 1/2″ diameter 1/4″ by 3/8″ and then, of course, my vacuum pump. No special fittings or anything anywhere very very simple setup and very effective. Just to give you an idea I’ve been running a total of 24 minutes right now and my decay test has another two minutes I’ve set for 10 minutes a day so another two minutes and we’ll be good to go and as you can see single hose setup very very effective and as you can see I have it isolated. I’m still reading my micron gauge and everything in the system.  Hope that helps just a quick rundown have any questions feel free to ask.
— Brad Hicks, HVAC in SC

Test your evacuation knowledge with this short quiz written by Jim Bermann

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This article was written by Jim Bergman with MeasureQuick

Anyone that has ever picked up a vacuum pump has asked or been asked this question, and to be truthful it is like asking “How many licks will it take to get to the center of a Tootsie Roll Tootsie Pop?” In the words of the wise old owl, “The world may never know.”

Modern day evacuation techniques are meant to degas and dehydrate a system, cleaning it of contaminants to a level that assures that non-condensibles and more importantly moisture will cause no harm to the refrigerant or the refrigerant oil in the system. Moisture with oil forms sludge, and moisture with refrigerant, hydrofluoric and hydrochloric acids. All of these can cause permanent damage to the refrigeration system.

How long an evacuation takes depends on many factors in this order, including but not limited to the size of the system, the level of system contamination, the diameter and length of the vacuum hoses, the presence of the schrader cores in the service valves, dryness of the vacuum pump oil and lastly the size of the vacuum pump.

More important than how long will an evacuation take is understanding when the evacuation is complete. Removal the air is an easy process, but the removal of moisture is much more difficult and simply takes time. Moisture has strong molecular bonds and does not easily free itself from the surfaces it attaches to. It takes heat energy and time for the bonds to break and a deep vacuum for the pump to ultimately carry that moisture out of the system.

The best advice that can be given, when it comes to evacuation is to make sure the preparation of the copper tubing is kept the primary priority. Keeping the system clean (contaminate free), dry and leak free during assembly will save far more time on the back end then the uncertainty it will introduce into the time required to clean the system through the evacuation process.

To properly clean (degas and dehydrate) the system, an accurate vacuum gauge is an indispensable component of the evacuation system. The use of an electronic vacuum gauge is the only way to determine when the dehydration process is complete. Using an electronic micron gauge like the BluVac+ Professional and its accompanying application will show you the characteristics of moisture allowing you to easily identify a wet vs a dry system. At 5000 microns, 99.34% of the degassing has occurred, but the moisture removal is just beginning. If you cannot achieve a vacuum below 5000, it is a good indicator of a system leak, a leak in your vacuum hoses, contaminated vacuum pump oil etc.

Once you are below 5000 microns you can be assured that dehydration is occurring and that moisture is being boiled off and removed the through evacuation process. Significant levels of dehydration are not occurring until the vacuum level is below 1000 microns.

When is comes to the vacuum gauge reading and the actual vacuum level, and an important distinction must be made. Pulling below 500 microns and being below 500 microns are two totally different things. A good vacuum rig coupled to a large pump can overpower the dehydration process, pulling below 500, but not removing the moisture which simply takes time. It is not until the vacuum has been isolated that we can determine the ultimate level of vacuum. Core tools are essential to isolate the vacuum pump and rig from the system when the ultimate vacuum level is being measured. The system needs to hold below the target vacuum to assure that adequate dehydration has occurred.

The following are guidelines for an acceptable standing level of vacuum. For systems containing mineral oil like R22 systems, a finishing vacuum of 500 microns with a decay holding below 1000 microns generally considered acceptable, whether we are talking a new installation or a system opened for service. For the system containing POE oil, like that of a R410a or R404a system, a finishing vacuum of 250 with a decay holding 500 microns or less should be achieved, and never a decay rising over 1000 microns on an R10a system opened for service. For ultra-low-temperature, refrigeration, a finishing vacuum as low as 20 microns may be required with a decay holding below 200 microns, for these systems, consult the manufacturer if at all possible. Each of these requirements is focused on the acceptable level of moisture remaining in the system, again because at these levels the majority of degassing has already occurred. The time allowed for decay depends upon the size of the system, but generally, 10 minutes minimum with 1 minute added per ton is a good guideline.

The moral of the story is this. A proper evacuation may take 15 minutes, 15 hours, or 15 days. It simply takes what it takes. While removing cores, using large diameter hoses, clean oil, and a properly sized pump will definitely shorten the time required to complete the process, the true time required is a function of the cleanliness and dryness of the system being evacuated.

Evacuation cannot be rushed or shortcut because the consequences are far worse than the lost time in the process. The best and most important thing to remember is cleanliness in next to godliness when it comes to preparation and finally evacuation. This means keep the system piping clean, your vacuum rig clean, the oil clean, and follow good processes. This is a point that cannot be understated when trying to shorten the time required to complete the process properly.

Jim Bergman
MeasureQuick

This topic came up because I was testing out the new MR45 digital recovery machine and that machine goes off by itself when it hits a 20″ Hg vacuum. This is a cool feature but it is good to know when that level of vacuum is overkill and when it’s not enough according to EPA requirements.

Why would you need to recover into a vacuum you might ask? Well, so long as you are above a PERFECT VACUUM (and you always do) there are still molecules of refrigerant in a system even at 0 pisg (14.7 PSIA at sea level). In low pressure systems like centrifugal  chillers the entire system charge can often be in a vacuum when the system is off, this means that recovery on these systems means you START below 0 PSIG and go down from there. 

First off let’s pretty much assume that none of you are using recovery machines OLDER than 1993 so really only look at the right side of the chart above.

If you are working on an air conditioning system with UNDER 200 lbs you are safe taking your recovery to 0 or atmospheric pressure. If the system you are working on has OVER 200 lbs of refrigerant or if you are working on a medium pressure or low pressure system you will need to pull the system into a vacuum.

The EPA does make an exception if the system has a know leak and pulling into a vacuum will result in contamination of the recovered refrigerant. Here is an excert from the EPA final rule summary from 1995 (still in force)

Also let me clarify that 25mm hg absolute is another way of saying 25 torr or 25,000 microns, it’s just a finer scale and it goes from 760 torr (760,000 microns) down as the vacuum gets deeper whereas inches of mercury (“hg) goes up as the vacuum gets deeper.

— Bryan

First I want to give credit where credit is due. This post is made possible by the fantastic demonstration video by Neil Comparetto that I embedded below.

Before you get bored and stop reading I want to give some conclusions. Ice can form in a vacuum, but I still advise pulling a fast, deep vacuum in most cases. Now… keep reading to see why.

The statement that is often made by techs is that pulling a vacuum “too quickly” can result in freezing of the moisture inside the system and reduction of evacuation speed. This conversation usually occurs when another tech is demonstrating a SUPER FAST evacuation, or by a tech who is advocating for the consistent use of triple evacuation.

Neil’s video proved that pulling a deep vacuum quickly can result in freezing with even a small amount of liquid water present. He also demonstrated that this is possible with a typical HVAC hookup and that it can pull down to 500 microns with substantial ice present. This was done in 50 degree shop, with a glass jar (insulator), with relatively low internal volume, pulled down using a vacuum pump direct connected with large hoses.

So he proved that under certain circumstances, ice can form and cause a real problem with evacuation speed and even trick a junior tech into thinking they pulled a proper vacuum when they did not.

So what causes this and how do we prevent it?

Water, like all substances, changes state due to the molecular density and configuration based on the pressure surrounding the molecules and the temperature of the molecules (average molecular velocity). When we pull a vacuum on water there are two opposing forces, on one hand we are DECREASING the pressure which leads to evaporation and then boiling, but as the water boils it begins to lose heat because that molecular energy of the highest velocity molecules are being evaporated and removed by the vacuum pump, thus reducing the average molecule velocity (temperature). The key reason why it can freeze in these experiments is because the heat rejected through evaporation / boiling is significantly higher than the heat ADDED through the sides of the jar which is why it starts by flashing, then boiling, then back to liquid then freezing. You are WATCHING the change in energy state in real time as the available heat in the jar and added through the walls is overcome by the heat REJECTED from the boiling liquid and out the pump.

Now, if the pump was left on the ice long enough, the ice would eventually all SUBLIMATE (change directly from solid to vapor) but the rate at which that would occur is based solely on the amount of heat being added to that ice through the walls of the jar. This addition of heat is equal to the differential in temperature between the ice in the jar and the temperature around the jar.

The deeper the vacuum pulls the colder that ice will get, which will increase the differential between the ambient around the jar and the ice temperature inside.

If we hit the jar with a heat gun, the ice would melt quickly because we are ADDING a huge amount of heat very quickly. In the same way, if the ambient temperature in Neil’s shop was higher or if the vessel was made of copper (conductor) instead of glass (insulator) it would be less likely that ice would form and if it did form it would sublimate more quickly.

Here are my current conclusions based on this video (and many others), good science and practical field experience

  • It becomes increasingly more important to employ triple evacuation and using a heat gun as ambient temperatures drop
  • Liquid water inside a system should be exceptionally rare, follow good copper handling practices and don’t work with open copper in the rain.
  • When the internal volume of the system you are evacuating is very small it would be easier to create ice (ice machines, ductless linsets etc…) use more caution in these circumstances by employing triple evacuation / breaking the vacuum with nitrogen / sweeping with nitrogen.
  • Most important is to valve of the micron gauge from the pump and watch for rapid increases. If you have ice you WILL see and quick increase when the micron gauge is isolated from the pump in the system.
  • Use a quality micron gauge that can show you a decay / leak rate so you can easily be aware when there is an issue.
  • When you are pulling a vacuum on most systems, during warm ambient conditions you are RARELY if ever going to make ice in a system under vacuum.
  • The conclusion is NOT to pull a SLOWER vacuum, it is simply to use heat and breaking the vacuum with nitrogen to get the moisture removed.

Here is the video-

— Bryan

fusite_plug

This tip will be like an episode of Columbo, we will start with the what and who and then get to the why.

  1. Don’t pump down a scroll into a vacuum
  2. Don’t run a scroll in a vacuum
  3. Don’t run a high voltage megohmmeter or Hi-pot test on a scroll (As a general rule don’t go over double the rated running volts)
  4. Don’t do a any megohmeter test with a scroll under vacuum

These points have been confirmed with Copeland (Emerson) as being on the naughty list this Christmas.


Resistance / Megohm Testing

A scroll is like any other compressor in that it has a motor and a compression chamber “hermetically” sealed inside the shell. There are many differences between a scroll and a reciprocating compressor but let’s focus on the few that are pertinent to this conversation (or at least the pertinent ones I can think of).

  • In a scroll, the motor is located on the bottom, this means that the motor is immersed in refrigerant and oil. When the compressor has been off and is cold, there can even be some liquid refrigerant in the compressor.
  • A scroll is more compact and balanced design as there is no need for “suspension” like a reciprocating compressor. This results in closer tolerances / distances between the electrical components and the other metal parts.

The motor being located at the bottom is the biggest thing. Copeland states in bulletin AE4-1294 that megohm readings as low as 0.5 megohms to ground are acceptable. Besides that fact that this makes a scroll difficult to successfully meg (essentially impossible with a tool like the Supco M500 because it only reads down to 20 Mohms) it is a clear indication that a scroll compressor is running tighter resistance tolerances and a higher risk of internal arcing due to many factors. Another thing to consider is the scroll will read lower ohms to ground when it is cold than when it is running due to higher refrigerant / oil density at lower temperature and of course you are generally doing a meg test when a scroll has been off…. so that makes it tricky.

Some of the factors that can decrease resistance further and lead to problems are:

  • Moisture contamination
  • Free metallic particles due to copper leaching (acids), small metal pieces left from copper fabrication or metal from compressor breakdown due to other issues like overheating, flooding and improper lubrication.
  • Other contaminants

All of this to point out that tolerances are tight in a scroll to begin with.. add in some extra nastiness and you are at risk.


Pump Down 

First, many scroll compressors won’t even allow you to pump them down into a vacuum. Either they are equipped with a low pressure cut out or some sort of low pressure / low compression bypass like shown in this USPTO drawing

vacuum_prevention

For example, in Copeland AE4-1303 it states “Copeland Scroll compressors incorporate internal low vacuum protection and will stop pumping (unload) when the pressure ratio exceeds approximately 10:1. There is an audible increase in sound when the scrolls start unloading.’ This is to prevent the compressor from pulling down into a vacuum.

In addition to that there are lot’s of threats and warnings about running a scroll while it is in a vacuum, as in, if you had just evacuated the system and then accidentally turned the system on. Which is a bad idea on any compressor, but worse on a scroll.

Why?

The totally obvious reason is that the compressor itself isn’t designed to run in a vacuum and it will overheat as well as fail to lubricate properly, but that isn’t the only reason or even the primary reason.All of the literature mentions arcing and I spoke to more than one tech rep who mentioned the “fusite” plug arcing or being damaged.

First, Fusite is a brand name and one of the companies in the Emerson family. So when we say “fusite” we are using a ubiquitous term for a sealed glass to metal compressor terminal feed through. There are many different types and  designs of Fusite terminal just as there are many different types and designs of compressor. There are scroll compressors that use them, there are reciprocating compressors that use them, the ice cream truck that plays that obnoxious music driving through your neighborhood probably has one…. on the refrigeration compressor. Do certain fusite terminals short out more easily than others? I’m sure some are more susceptible than others. Is that what is going in here… maybe.. but if so it’s only part of the story.

What we do know about a scroll is the electrical tolerances are tighter… and when electrical tolerances are tighter there is a greater likelihood of arcing.

It’s about to get really nerdy here so if you don’t care just stop reading and go back to the very beginning, memorize the 4 points and move on with your life.

I can’t do that… because I’m broken.


Why is vacuum an issue? Isn’t vacuum the absence of matter and isn’t matter required for electrons to arc from one surface (cathode) to the other surface (anode)?

The answer is not really simple AT ALL but the summary is that under certain circumstances vacuum increases the likelihood of arcing and scroll compressor terminals inside the compressor happen to be one of those circumstances.

First thing to remember is that while electrons do travel through matter, electromagnetic fields do not require matter to exist and in either case.. we are incapable of achieving a perfect vacuum so no matter how deep we pull a vacuum, some molecules are still present.

I’ve some some techs attribute this to the corona discharge effect which can occur due to the ionization of particles around a high voltage conductor. I really don’t see this as being the answer both because the voltages applied are not THAT high and corona discharge is not a arc or a short in the traditional sense, just a “loss” to the environment around the conductor and a pretty cool looking light (as well a decent Mexican beer).

My opinion (and this is an opinion not a fact) is that the arcing is due to something called field electron emissions which can result in insulator breakdown in vacuum conditions (NASA has to deal with it all the time in space because space is a vacuum ).

The conclusion is that while this phenomenon can happen in ANY compressor, it is made more likely in a scroll due to tighter tolerences and “motor down” configuration. This means that doing a high voltage meg test, or any running / meg testing under vacuum is a bad idea.

If you want to read more about Fusite, Copeland scroll compressors and a great overall guide that includes evacuation procedures just click the links.

Nerd rant over.

— Bryan

 

 

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