reading gauges

[trevor389]

hi im pretty new to this and new to air con and am hoping to pick up some tips . ive a fitter in a workshop and have done a r404a course but was not very spesific to the jobs i need to do . we have a full fleet of hubbard fridge trailers and i ve been told that the pressures should be 15 bar high side and 3-4 low side. but i really dont understand how to tell when a fridge is low on refrigerant. i ve done a few and it was a complete guess . i recovered the gas and weighed it and repaired the fault and regased. i d really like to lern how to acctually read the gauges on the system and understand how to tell if a system is low on refrigarent. the last one i had the suction pressure was 8 bar and the high side was 8 bar and it only had 2kg of gas in. the system holds 11kg. any ideas ? thanks

[sedgy]

hi trevor,
its important that you do a gas handling course, - so that you can work leagally,
and when you talk about pressure , a bar is very vage psia is more define-
and then when you put your gagues different gasses. at different tempritures stand at different psi so you well need a comparitor to see the temp . at the psi it is standing or what the discharge + suction is when its running .
on the job you quoted both sides where 8 bar cos it was not running< stoped< on my comparitor 8bar< Pe< is about 130 psia. hope this helps
sedgy.

[airefresco]

Pressures don´t really tell you anything useful on their own.

Ready Gary´s thread Refrigeration 101 (http://www.refrigeration-engineer.com/forums/showthread.php?t=19701)
It will help you a lot.

[cool runings]

hi im pretty new to this and new to air con and am hoping to pick up some tips . any ideas ? thanks


The thing is refrigeration is a technical trade.
You can learn on the job but you need help and somone to show you.
Is there no one there to help you? What about your employers, do they expect you to work on the system without training?

You say you are a fitter!! Would you be able to do your job without training or help?

People here would willingly offer you advise but most on here know that to help you would not be right and you could do more damage to the systems you work on than you help..

I know thats not what you want to hear but it's not fair that you are expected to do this work without training. Your employers need to get you some training.

All the best

coolrunnings

.

[nike123]

http://www.refrigeration-engineer.com/forums/showthread.php?t=11383

[trevor389]

thanks for the reply guys . all i have done is the r404a course and yes they expect me to repair all fridge faults on our trailers. no more training will be given aparantly thats all u need is this legal ?

And yeah your right i wouldn t be able to do my job without someone showing me.

Sedgy yeah the fridge was running but the comp kept cutting out on LP. the suction was going to 8 bar then dropping to below 1 then the comp would cut out. I really would like to understand how theses pressures tell me whats going on but strugleing to understand really. Really appretiate the help guys think ill be on this site quite alot from now lol.

[sedgy]

hi trevor ,
yes there is a problem with this system , its short of gas , you say there was 2kg of gas in it, so you have removed the gas once ? did you leak test? it needs ofn BUT THE PSI IN A BOTTLE OF OFN IS 2500 PSI THIS IS VERY DANGOROUS FOR UNTRAINED OPPROTIVES TO WORK ON , you need training ,your employers need advice to there responsabuilities to thire workforce

[trevor389]

yeah i removed the gas weighed it at 2kg the system holds 11kg . i leak test it with nitrogen found the faulty pipe made a new one. vacced it over night and regassed the system and it worked fine . i am pretty confident at doing this its just the gauges that i dont know whats going on according to the pressures etc . and i will be getting no more training. hard ressesion times . can u give me any info on reading gauges . thanks for the help its really appretiated

[glenn1340]

Your employer is so shortsighted (as if you didn`t know) a basic course at a decent traing centre will cost them less than a grand, plus the C&G 2079 which you`ll need anyway. It`ll cost them thousands more each year to get a contractor in to do the repairs. I was approached by another company as it was paying nearly £40000 a year for a contractor to fix thier dryer breakdowns. Then you`ll have a grounding to work on small fridge systems.
As you`re a skilled fitter the mechanical side should pose few problems. Plus you have the advantage of being in a workshop without a customer breathing down your neck. Then it`s just a learning curve. Oh plus a few ****ups along the line....we`ve all done that!

[sedgy]

yes glenn . your spot on, but just to go back to trevors point, and to get the point over, he said he pressure tested, found a leak. < ok < fitted a new pipe , evacuated all nite added the gas ran on test all ok BUT, was the system re- pressure tested? and after it was run on test was it re-leak tested? sorry but not being pikky. just making the point. correct procedure, trevor keep up the good work as we have all found out its not easy all the time , but the more times you do it right, the easyer it gets. all the best mate, sedgy,

[airefresco]

Sedgy yeah the fridge was running but the comp kept cutting out on LP. the suction was going to 8 bar then dropping to below 1 then the comp would cut out. I really would like to understand how theses pressures tell me whats going on but strugleing to understand really. Really appretiate the help guys think ill be on this site quite alot from now lol.

When you get a situation like this, it may not necessarily mean it is short of gas. If you had a blockage somewhere in the system ( a blocked drier for example) then you would get the same thing with the suction pressure dropping low (eventually in to a vacuum if there was no LP switch). If the pressure rises fairly quickly when the compressor switches off then it probably is gas, if it takes a while for the pressures to rises back up again then it is more likely a blockage.

Basically what im trying to say is low pressure doesn´t equal low gas. There are many things that could cause low pressure and you need to learn how to identify them and rule out other possibilities before adding gas. Topping up a system should be the last step to take after everything else is ruled out. Of course there are exceptions to this rule.