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Zane
06-07-2016, 09:59 AM
Hello and thank you for your time. I am a 2nd year apprentice from Aus and wanted to ask something thats been bothering me and none of the tradies at work have provided a good answer. How do I know how much gas I should be charging into a system? The tradies just say to keep slugging liquid until the sightglass seems full but i want to understand what im actually doing with the system. What should my gauges read and how do i know that my gauge readings are "correct" if i can see a full sightglass? What is a "correct" gauge reading for an underbench, a coolroom, a freezerroom etc and how can i learn to apprehend the differences quickly and independently using my brain and not a cheat sheet?

Also, what exactly is Temperature Difference, it's importance and how is it established? Is it a feature of design? If so, how can I apprehend that using information from the system I'm looking at?

Thank you. I really dont want to be stuck scratching my head when the boss eventually puts me out on the road so as much good, clear info you can give me the better. TAFE isnt much help either :S

HVACRsaurus
06-07-2016, 11:46 AM
Ahh, ye olde refrigerant in the sight glasses..

This question comes up a couple of times each year, half a dozen guys chime in with their take on the situation..

Try asking your tradies a different question, say, compare the debate of how much refrigerant should be in the sight glass versus the whole juggling act of day to day fridgie working life - consider the fault finding, replacing of compressors, fan motors & contractors, consider the one job to the next, the paper work, phone calls, emails, consider the problem jobs where nothing goes right. Consider the travel, late nights, early mornings, the often thankless achievements and doing what it takes to keep a system running - they will all admit, empty, full, who gives a rats rectum as long as the coffee is hot and the beer is cold.

You will face many many of challenges as time goes by, the "correct" amount of refrigerant in the glass will become your smallest concern - save your energy for the real problems.

Ps, check out this guy on the YouTube - he's got a bunch of great videos & is the master at keeping it cold!

https://m.youtube.com/user/heavydiesel?feature=em-subs_digest

Pps, temperature difference, I'll be quick;

Question - what would happen if the refrigerant in the evaporator was the same temperature as the surrounding air?

Answer - nothing! The thing would just run & run & wouldn't cool down.

That is why we need temperature difference - the temperature in the evaporator must be colder than the surrounding air in order to provide cooling..

B G Scott
06-07-2016, 11:55 AM
Read the best books on the basic principles to fully understand what is going on in any system.
You cannot just assume that there are a set of parameters that any one here can give you that will be a one size fits all solution the questions you pose.

Rob White
06-07-2016, 02:05 PM
.

Zane, you might think we are being deliberately reluctant to give you
the information you want. It is not that we are trying to make it hard
for you but it is the way you find out how it works, that will teach you
what to do.

I'll add to what Mr Scott and HVACRsaurus have said.

You need to know why we have a sight glass? Do we use sight glasses
with capillary tubes? Why do we have sight glasses on expansion valves?

We need pure liquid in sufficient volume supplied to the valve for it to work,
how do you know if it is full bore liquid? Temps and Temp difference are more
accurate than sight glasses because sight glasses show you what is happening
but temps prove what is happening.

Has you trainer talked about subcooling? I would hope so, so if you know about
liquid subcooling, knowing about temps and temp difference is important.

We are not being deliberately obstructive, we just don't want to answer any of
your homework questions :D

Do keep the questions coming and as you start to work through them we will
work through them with and point you in the correct direction.

Regards

Rob

.

chemi-cool
06-07-2016, 02:59 PM
Hi Zane and welcome to the forum.
On this site you will find some good stuff, http://sporlanonline.com/literature-and-educational-materials/

Always, when something is not clear, do not hesitate and dig for answers and understanding.
This will make the difference between yourself and guys who just do as they told without understanding what is it for or why.
Refrigeration is fascinating and if you will be good at it, it will pay you back.

Recoilzn
06-07-2016, 08:00 PM
Hi Zane and welcome to the forum.
On this site you will find some good stuff, http://sporlanonline.com/literature-and-educational-materials/

Always, when something is not clear, do not hesitate and dig for answers and understanding.
This will make the difference between yourself and guys who just do as they told without understanding what is it for or why.
Refrigeration is fascinating and if you will be good at it, it will pay you back.

Nice site chemi

RANGER1
06-07-2016, 08:36 PM
http://www.refrigeration-engineer.com/forums/showthread.php?19701-Refrigeration-101

This might be a good start

niceman
06-07-2016, 09:57 PM
Zane, take it from an oldie, you've got a lot to learn, l was still learning up to the day l retired. It will all fall into place for you, the fact that you have contacted this site shows you are keen to learn, so your halfway there. When l was just out of my time, every query l put to my manager he said, "your on a learning curve " On a tough day l rang him and told him " All my learning curves have joined up, and now l'm going round in circles!!" Welcome to the world of fridgies, its awsome.

mikeref
07-07-2016, 09:07 AM
Zane. You have 4 years to learn this trade's principles. Don't try cramming your 4 years into 2. The people you work with were once in your current position.... How? What? Why? When? etc will be answered as the Months go by.
Mandatory block training for Second year Apprentices should show you how to understand
Psychrometrics (https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwj93eOd8eDNAhXHjJQKHe86CpYQFggqMAU&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPsychrometrics&usg=AFQjCNH_HEUhLqlGZSgUfnbhucnitXhOrg)

PS...Sheet, this ^ link might have been a little to aggressive.