running pressures

can anyone please tell me how it is when i see other fridge engineers at work the just charge a system to a certain bar or when they connect there gauges they can tell straight away if there a problem even though there is a positve pressure and its only 2 or 3 bar wrong i am at college and am taught you should always weigh it or check other signs but these blokes SEEM to know straight away is it right or wrong what they seem to be doing i know it a basic question but when i ask anyone all they say is its expierience and i will learn it as i work on more systems

sean

if you learn the basic refrigeration cycle diagram inside out and truely undestand it then you will know too..

cheers

richard

Hi Sean1

Have you ever been to the Doctors?

You tell him what your symptoms are and he then knows what the problem is. All he usually uses is a stethascope (sp), thermometer and blood pressure gauge. It is the same for any trade or profession. You learn the basics at college and the rest you learn by experience.

You have to have a good understanding of the theory and how it should work before you can determine if it is working correctly. A good fridge engineer gets a "feel" for a system just by connecting gauges, measuring amps and taking temps.

Have patience, if you are really intersted in the job then learn all you can and read good books on the subject.

thanks for ur replys i have been working fridge 4 a few years but mostly simple faults eg.fan motors, blocked condensers etc. i know a bit of the basic but mostly phsical faults in a system which aint hard to find. i am interested in the job a lot i just finish my first year at willesden colege i have a fridge book called modern a/c and refrigeration i dont know the author but its a large blue one from america can u recommend any other books? we have learnt the refrigeration cycle but it only covered what the physical state the refrigerant was at set points in the system eg.superheated or sub-cooled etc if u know a book that covers this in more detail it would be greatly appreciated

Quote:

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Originally Posted by sean1

can anyone please tell me how it is when i see other fridge engineers at work the just charge a system to a certain bar or when they connect there gauges they can tell straight away if there a problem even though there is a positve pressure and its only 2 or 3 bar wrong i am at college and am taught you should always weigh it or check other signs but these blokes SEEM to know straight away is it right or wrong what they seem to be doing i know it a basic question but when i ask anyone all they say is its expierience and i will learn it as i work on more systems

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Waw, you definitely has taken a large breath after reading this sentence.
Don't forget Sean that this is a worldwide forum and not everybody speaks fluent English.
Therefore, you should better use points between your sentences.
I even stopped reading after the first two lines.
My kids have this similar strange behavior due to a lot of chatting via the net, they even use words I can't find in a dictionary. (w8,txs, 4 you, ...)
Or, I'm beginning to get an old man.

haha sorry peter_1. i will try a bit better with my grammer. can you recomend any refrigeration books.especially to do with a refrigeration cycle

No peter , you are not aging , but try this 10x , omg , tyt what do you think of that :
10x: thanks
omg : oh my god
tyt: take your time

I though that i'm outdated till i got familiar with those terms . . . so try to keep tracking the chatters inventions for abbreviation because almost everyone is using it after a while from it's first release.

Sean 1 , experience and a good knowldge of basics are your tools utlimate tools to solve problems

cheers botrous
but i dont feel i know enough of the basics. its only the last year i have started to use gauges. there still a lot to know ON THE BASICS. which is what i hope to learn through college and talking to people in the industry. i hope peter approves of my grammer in this post.hahaha
no ofence peter only joking

Quote:

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Originally Posted by sean1

can anyone please tell me how it is when i see other fridge engineers at work the just charge a system to a certain bar or when they connect there gauges they can tell straight away if there a problem even though there is a positve pressure and its only 2 or 3 bar wrong i am at college and am taught you should always weigh it or check other signs but these blokes SEEM to know straight away is it right or wrong what they seem to be doing i know it a basic question but when i ask anyone all they say is its expierience and i will learn it as i work on more systems

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People who take such shortcuts can, with experience, fix most systems just well enough to get by (unless/until they run into any problem that is out of the ordinary). They are by no means fixed right, and the ability to take shortcuts is not something to be admired or copied. It's just laziness.

Not too surprisingly, I recommend my books. They are exactly what you are looking for. Just click the link in my sig line.

BTW, it's not about running pressures, it's about running saturation temperatures. In the case of R22 you can read these on the green numbers (R22 scales) on the gauges. For other refrigerants you will need a P/T chart.

It is good to see new blood in the industry, during the last 15 years in my area there has been a massive skills shortage for refrigeration engineers which is good in the way that most companies in Staffordshire are now self employed one man bands so excellent for us. Regarding books, search Amazon or even e bay, lots of bargains to be had. Also when diagnosing a problem on a system, just feeling the suction, discharge and liquid line prior to installing your gauges will tell you a lot about what is going on. I would suggest that you become familiar with the popular types of gas, operating temperatures of different systems and evaporating temperatures. Once you know what the ideal evaporating temperature is, you are half way there. A rule of thumb regarding recharging systems, if it has an expansion valve and sight glass fitted, charge it to a full sight glass, if it has a capillary expansion device, the charge is critical and weigh the charge in with scales or a charging still, a worth while investment and everytime you change a compressor, replace the drier and physically blow through the old drier before throwing it away because if it is on R134a I bet it is either partially blocked or blocked solid.

Sean,

Search like Andy W said on Ebay under refrigeration, and books.
Modern Refrigeration and AC from Althouse, Turnquist and Bracciano are very good with very nice drawings and schematics.
If you want to learn the theory very good and start from the real basics, then I can highly recommend Dossat.
You can find them also second hand.

I still disagree Gary the TECH method your teaching.
I don't say that they're not usefully but you have to know first the basics before handling a refrigeration unit.

If I give your book to someone who never read something before, he will just perform some - I agree - logic steps but he will not know what he's exactly doing.
It's like learning a monkey some nice tricks which he will reproduce exactly the way you teach him but that monkey will never know what he's doing.
I know, you believe in your books, otherwise you shouldn't have written these books.
I will keep saying it: you first have to learn the basics and I think most posters follow me in this idea.

As far as I remember, I even didn't see any lop/P chart in all your explanations.
What if a tech has only a log/P chart as a tool with him?

I once had a tech who had to install a cascade system for a Meissner coil with propylene in the high stage and ethylene in the low stage. The only thing he needed was the address of the client and two log/P charts and vapor/temperature charts. This is for me a real tech, one out thousands.

You also start in one of the first pages of your book with saying how to measure subcooling without first explaining what subcooling realy is and why you need it, what he benefits are by increasing or decreasing it.

All the condensers on smaller units aren't fitted with a subcooling 'device', so there is no substantial subcooling.

You also stated - that's one of the things i still remember because I have written it down - that most techs fill the sightglass till it's full following direct that most systems are then overcharged.
I throw this statement in this forum: what do the other guys think?

I rarely use my thermometer but use my hands and feel all the lines. Perhaps I developed this way a not so common skill but that's always the first what I'm doing if there is a problem with a unit. Diagnosing this temperatures guides me in many cases to the probably cause.

You say that 8K subcooling is excessive but we have units running with much lower subcooling, even 40 K, yes even 50 K so if I follow your book, then something is wrong with our plant.
If you understands the basics, then you should see that this is a normal situation. If a tech should arrive with your book and follow the flowcharts, he should think that something is wrong and evacuate the whole system and refill it till he comes to the 'common' subcooling. It should never work.

Sean,

I agree with the the people who say learn the basics. Do not fall into the trap of thinking the suction pressure and discharge pressure are the same. This also applies to discharge pressure and condensing pressure. Each one is a separate point of reference.

Also, at each point you measure the pressure; check the temperature. The two reference points (pressure & temperature) tell you what the refrigerant is doing. You have to learn how to visualize how the refrigeration system works from the inside. You can only do this if you understand how the refrigeration system should work.

Learn the difference between subcooling and actual liquid temperature. Understand what superheat is and where it occurs. Superheat also occurs in other parts of the system besides the evaporator.

Also learn what saturation temperature really means.

Use the pressure-temperature (P-T) charts for everything. After you get comfortable with these, start learning the pressure-enthalpy (P-H) diagrams. With the P-H diagram you can see what condition the refrigerant is in (liquid or vapor, and if it is subcooled or superheated).

Another way of learning more is to pick up the manufacturers catalogs. Learn how their components work. And just as important, learn how they recommend to select the components. Thermostatic expansion valves, refrigerant distributors, and distributor tube selection is a very interesting topic.

Read, Read, and read some more. But also apply what you are learning. Before long you will become one of the old timers who can hook up gauges and feel what the probelm is.:D

All of the basics will prove very beneficial when you go to work on other refrigerants and systems. Basically, an ammonia system works the same way as a supermarket system. The only differences are the components, how they work, and how the components are used in the system.

Stick with it. This can be a fun business. The guys who know the business really well are always in demand.

Best of luck to you,
US Iceman

I think you need to read the book again, Peter. Subcooling of 50K at the receiver outlet, which is where I recommend measuring it, means your condenser is full of liquid.

Is it getting hot in here , or it's just me feelling the heat . . .
Basics of refrigeration are the basics of a good tech . . . experience plus theory = excellent tech . . .
Anyone who wants to advance in this field should have a good "ammunition" of theorical knowldge and a good field gained "ammunition" that is the experience.

Sean,

I did some research in my library for other books that may be of interest to you.

The one Peter mentioned; Modern Refrigeration & AC is a good book to start with. I used the first edition of this book when I was in school.

Of course, a really good book is "Principles of Refrigeration" by Roy Dossat

Some others are:
1) Principles of Refrigeration by W.B. Gosney
2) Applied Air Conditioning and Refrigeration by C.T. Gosling
3) Refrigeration Principles and Systems by Edward G. Pita
4) Industrial Refrigeration Handbook by Wilbert F. Stoecker

You might also try some second-hand bookstores. I have found several good books in these for reasonable prices.

Hope this is usefull to you.

Best Regards,
US Iceman

Sean
It just appears the are using their gages, but to analyze the problem they must have more data. Critical charge units must be weighted in. Non-critically charged units generally require pressure readings and superheat and sub-cooling readings to properly evaluate system performance.

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Originally Posted by US Iceman

2) Applied Air Conditioning and Refrigeration by C.T. Gosling

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I'm gald to see that C T Gosling's book still crops up from time to time. I thought that it was out of print.

I worked for Trevor Gosling's company, DES in Commerce Way, Croydon, for several years in the late 70 - ealy 80's, and my copy is definitely dog eared.......bit out dated, but still a good general book.

.
________
herbalaire review

DES went tit's up didn't they ?

From what I remember tescos withheld payments and bankrupted them (every little helps ;-)

cheers

richard

?Must be another one.

DES (Ductwork Engineering Systems Ltd.) became part of Carrier Holdings in 1983.

Never did any work for TESCO in those days. They were a Weathermaker account.

(We never went North of the River!)
________
volcano digital review

oh sorry

however you must remember old jc-ac then ?

cheers

richard

Indeed I do.

JC sold his pub and went back into 'the old game' the last I heard ( a few years ago).

His lad is still in the game though.
________
hash honey oil

I joined this site cos I wanted the P-T charts ... sounds like everyone is reluctant to give the figures out ??? anyone know where i can find them online?

Gordo,

Hi and welcome to the friendly RE forums.

Interesting first post I must say.....

Never mind,
All suppliers / manufacturers should be able to provide PT charts for the gasses they make/distributes.
However, he who search will find. A good place to start your search would be in the engineering section of my website ( www.the-viking.eu ), the PT chart you are able to download there covers most commonly used gasses. If you know what refrigerant you need the chart for and it's not on that list, then the easiest thing to do would be to look at the manufacturer's website.

Good hunting.

Quote:

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Originally Posted by gordo_guero

I joined this site cos I wanted the P-T charts ... sounds like everyone is reluctant to give the figures out ??? anyone know where i can find them online?

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Yep, if you download Coolpack, you all have them in one time.

Has anyone used/read the South African refrigeration engineer's book and CD "heat, energy and refrigeration".
Is it worth obtaining a copy?

Gary's books give a sound structural approach to getting a system to work properly!
Many of the problems posted on this forum could probably be solved by taking the full range of measurements advocated and using his logical approach.
Alan B.

Cheers Viking, PT chart was just the job! your site has lots of helpful downloads like the fault codes etc.
I am just building up a referance folder of useful bit n pieces, so thanks!
PS. Peter ... where is Coolpack though?

Quote:

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Originally Posted by gordo_guero

... where is Coolpack though?

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Coolpack is a utility that you can get here from the Technical University of Denmark - follow the links to downloads:


http://www.et.web.mek.dtu.dk/Coolpack/UK/About.html

If I Google Coolpack + refrigeration, then I get more than 2000 hits.

.

If you Google 'coolpack' you get this return at the top - first hit


" Energy Engineering - CoolPackCoolPack is a collection of simulation models for refrigeration systems. The models each have a specific purpose e.g. cycle analysis, dimensioning of main ...
www.et.web.mek.dtu.dk/Coolpack/UK/index.html - 8k - Cached - Similar pages"

The Danish Technical Institute moved the link to a new home last year, some time.

Whatever, it's an excellent little package.


.

despite what almost everyone of these self proclaimed experts will tell you, NO ONE knows everything there is to know, no matter how many years they have been at this, for example, read my post "hot compressor" despite all the info I have givin, no one seems to know what wrong!!! Some things just defy logic!!!

Quote:

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Originally Posted by jstch00tme

despite what almost everyone of these self proclaimed experts will tell you, NO ONE knows everything there is to know, no matter how many years they have been at this, for example, read my post "hot compressor" despite all the info I have givin, no one seems to know what wrong!!! Some things just defy logic!!!

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If you didn't noticed, we still demanding data from you!;)

Quote:

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Originally Posted by jstch00tme

despite what almost everyone of these self proclaimed experts will tell you, NO ONE knows everything there is to know, no matter how many years they have been at this, for example, read my post "hot compressor" despite all the info I have givin, no one seems to know what wrong!!! Some things just defy logic!!!

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No ones everything, that is true. Which is why forums like this are useful, to learn and share with others. Secondly you know it's that much harder to diagnose a system when you yourself aren't there, and can't test anything yourself. It's even harder when you have people not supplying all the information necessary in the first post and you have to pull teeth to get more info. :)

So you replaced the compressor, did you replace capacitors and relays? Did you think maybe a wiring fault since the old compressor and new compressor have the same symptoms? Make sure the relays are the right way up, the mains power and neutral are good, and there's no other wiring stuff ups in the terminal box.

edit: I haven't got back to it since I hadn't had the time to do all the conversions. I only work in Kpa for pressure or degrees C for temperature so I haven't got my head wrapped around your info yet.

sorry about the post guys, what i ment to say is that although he may have seen a few people nail a problem quickly, even the best get stumped every now and then, and dont let anyone tell him otherwise. again I am sorry for the way that sounded and want to thank everyone for thier help!