Refrigeration

You should have a charging valve in the suction line and an additional valve in the liquid line....

Thanks Solar Eagle two of them, from a vacuumed system which would be used first? I suppose the low side before the pump now question 2 when would one need to inject at the liquid side? Thanks again.

On a system that's been vacuumed and ready for start-up, I generally bleed liquid into the liquid line being careful not to freeze the valve(the valve can freeze in the open position), when frost starts to show on the valve stem, pause charging and wait for it to thaw, which it does quickly, resume until pressures equalize, you should have the approximate charge then in the system....Once the system has started, let it run for a few minutes for the pressures to settle down, then any additional charging is done through the suction fitting....Cross check the air temperature drop across the evaporator coil and temperature rise across the condenser coil....

As SE's diagram shows the system I typically have always done my system evacuations and recharge work from the low side and only use the high side port for pressure reference to make sure the expansion valve is working and the pressure differential between the two is within the expected working range.

Once you get the hang of it phase change heat pump systems work is not very difficult to do. In fact once you get comfortable with it and how they work and are designed it will likely make yo pretty disgusted with what HVAC technicians charge for doing it. (trained monkey work in most situations)

Thanks TCMTECH and Solar Eagle , Both are a big help, years ago I met on occasion an old HVAC guy and even though I was not a refrigeration man I kept my ears open and my mouth shut and learned quite a bit. I asked about pressures and lbs.of refrigerant and his answer is just inject until you the the temperature you want and that is just what the system needs. When I worked at the steel mill in very hot weather the crane AC units would fail to cool and when I called the AC Techs all they did was increase the pressure and the unit would cool the pulpit again. We are never too old to learn it there is desire. Thanks.

As a highly trained monkey I can assure you that we feel the same about know-it-alls like you....

I am a somewhat trained monkey. I still have trouble (at times) locating which is the low side and which is the high (liquid) side on my wife's Camry.

That is why it is good to have a mechanic buddy to call.

Just because you can make something look harder and more complex than it needs to be doesn't mean it's actually a difficult thing to do.

Maybe if it was a custom complex multi zone commercial system that required a moderate degree of smart logic control , yea I'd say it's not that easy but if it's just a common home central AC system no frigging way.

I've got personal equipment were doing oil and filter changes is more work and complexity than doing a basic home or mobil AC system check and top off.

Well I wish I was still in business and I could take you out on some calls so you could show me how easy it was....You probably couldn't even find the house... haha....I've seen it many times....

I have worked as a service tech in one fashion or another pretty much all my life and have been considered above average on finding locations will before GPS assistance was ever in place.

Even now in our oil fields finding places with GPS assistance is still largely useless being many well pads are located in what the GPS system se as fields and pastures with no roads. Even worse when dealing with well pads in the badlands where it could be a 5+ mile drive down a rough cut road with numerous unlabeled forks in it just to get to a well site that could be seen from the highway just be over a ridge.

Service calls of any form on any subject I have working knowledge and experience I can use to relate to it on do not scare me. If anything I thrive on the odd ones no one else wants to go on! Especially the ones where senior techs think they can beat me because they thing whatever it is is 'too hard'.

I'd take your service challenge any day and even bring my own tools to boot and you can stand idly by and glare at me with as much disdain as you want but bring your lunch because if it's a hard one we may be there for a long time! I don't quit until I have found the problem and have a solution to it.

Yeah well working in the city is a lot different than dodging herds of buffalo out in the sticks....and if you can't find the problem in 10 minutes or less you won't make the cut...and selling services to housewives instead of following orders from some hotshot in the fields requires a different set of skills...Don't forget your business license, liability insurance, certificate of competency and contractor's license filed in every city(about 20) you do business in, all need to be updated every year, and EPA certification...and probably a half dozen things I forgot...You'll need a work vehicle that has the company name and contractor's license number painted on the sides of the vehicle, no stick-on's allowed...Add to that about 20k worth of inventory, and you're ready to get started...You'll need to be able to design and price and schedule new installs on-site....in everything from high rise buildings to single family residences to commercial buildings...and this includes not only heating and AC but any type of ventilation, refrigeration, heat source recovery systems, electronic filters, and anything else you run across....You'll need to be registered and have an account at every supplier in town....You'll need to be able to make both sheet metal and fiberglass duct, and know how and where and when to pull permits in every city, and how much they cost...You'll need an office, dedicated phone line, proper forms and contracts, and advertising because nobody knows you exist....sound cheap? It's not, that's why the prices are so high....

So the issue isn't about the knowledge, skills or capacity to do the work then.

It's about the indoctrination and bureaucracy of your area and not the capacity to do the actual skills or capacity to do the actual work.

Sounds like a pretty lame/weak cop out me to try and get out of having to accept that I took you up on your claim being obviously I don't live where you do and thusly could not meet much of the local requirements you list any more than you could meet the equivalent requirements to work in my area either.

That's okay. No hard feelings on my part. If you have to resort to using bureaucratic technicalities not directly related to the knowledge and understanding of the actual technical work itself to justify yourself I have no problem with it.

I recognize a sore loser grasping at straws because he got called out on his claim when I see it.

(BTW, What would you have done had I sent you a PM showing I had all that in place? Claimed that because I have blue eyes and brown hair or aren't a member the local garden club in your specific neighborhood I don't meet some other standards and thusly am still unqualified? .)

Those requirements are what is needed to do A/C work, not including the ability to inspire confidence and ingratiate yourself to the customers. if you think they don't matter, than good luck to you....but putting all that aside, I still say you wouldn't be able to handle troubleshooting and repairing systems on a professional level....even if we stuck to "simple" residential systems....Oh sure you could probably find the problems on a lot of calls, but there are a lot that require specialized experience, and that you don't have...add to that the speed required to work at a level that is profitable is a lot different than a saturday afternoon tinkering session....

Hi Roy,

I'm starting a new thread, the last one seems to have gotten off topic.

What is your system going to be used for? What are you trying to cool, and to what temperature? Have you considered that you will run the risk of making dry ice when charging your system? Are you planning on designing a sub critical or trans critical CO2 system?

- Frost Forge

Hi Frost Forge: I suppose it will be a sub critical system at this time and as I learn more from information gained I will aim for a trans critical eventually. The device is intended to move heat from the atmosphere to a more desirable location or reverse system to cool a desired area. The intention is to use some of the energy from ambient heat to partially run the device for energy savings. The project is complicated by the fact that low cost components are not available due to the unique characteristics of R744 so I am experimenting with available components.

Roy,

Sounds like you have quite the project on your hands. I have some experience with commercial CO2 low and medium temp refrigeration, but it sounds like you'll be more in the high temp range (40-50*F SST). That means you could expect suction pressures in the 500-600 psi range and discharge pressures up to 1700 psi in the hot Ontario summers which would put you in the "trans critical" region. You had mentioned that you wanted to use liquid CO2 as the refrigerant. Keep in mind that when charging an evacuated system, you'll have to vapour charge it until you reach AT LEAST 70 psig otherwise you will create dry ice which will impede any further charging.

I'm not sure what compressors you're planning on using either, and I don't favour one over any other. But both Bitzer and Danfoss make CO2 compressors and have YouTube channels with loads of info you may want to check out (if you haven't already.)

I hope I've been somewhat helpful. Any other questions feel free to ask. Good luck with your project!

Thanks for the info. I have had some information on charging some conflicting such as heating the co2 and one video showed the tech. charging with liquid co2 and no heat. Regardless it should flash off into a gas if I do not push it. Soon there should be some open CO2 compressors as all European cars will have co2 R744 for 2018 model year. Due to my financial situation I am even using some hydraulic components in my prototype. I have had it running but not consistant and I have gages mounted in 5 places to see what is happening. AT 80 degrees F there is supposed to be 938 PSI which is a lot of stored energy.. I will keep the site posted as I proceed.

I've heard somewhere that if a two-chamber refrigerator, the charging port must be placed between the refrigerator and freezer. As far as it's true, I can't say. I'd like to hear specialist opinions. What are their thoughts, although I already see a lot of opinions here.