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View Full Version : Reasons for High Pressure / Low Pressure Trip outs



majikman
30-01-2007, 03:04 PM
Hi guys,

New to the forums so hello there !!!

Just an easy one really. On splits and vrv's what would be the reasons the systems would trip out on high or low pressures ?????

I have mainly been involved in the installation side and I am now looking to move over to the service side so need a little info.

I have a basic ide but would like to know the common reasons !!!

Also does anyone have any reccomendations for books I could carry around with me on a day to day basis that cover general air con ????

Thanks

Scott

Dr._Fleck
30-01-2007, 04:46 PM
Oh dear you are going to struggle..

LP trips for:
Low on gas
System blockage
Evap iced up/blocked
LP switch ****ed/set wrong

HP trips for:
Blocked condenser
High ambient temp
Overcharged
Wrong gas
HP switch ****ed/set wrong

erm.. that's all i can think of for now. Good luck, you're going to need it

p_p
30-01-2007, 08:05 PM
May i suggest you invest in some good rac training and spend at least 2years with a good service engineer. All manufacturers run really good courses and most are free.No offence but theres allready too many engineers out there that dont really know what its all about and if you dont understand hp and lp im affraid you fall into this catagory.
Dr Fleck is right you are going to struggle

The MG Pony
30-01-2007, 08:21 PM
Theres an old saying: If a job is worth doing it's worth doing right, and if it's not worth doing,,, Give it to rimmer.

(Lol I love red dworf)

Any case mate I'm with the others, if it is worth it for you to get into it, it is worth you geting into it right!

Take your time to learn, then get your self an old A/C and tourture it untill it breaks, then fix it and repeat untill the poor thing is replaced with brand new parts to the point you have a new A/C or it plainly won't work any more, thats just one model but will give you real life issues to work on that are dynamic.

Oh and design and build one, once you under stand them well enough to do that you will have no worries.

monkey spanners
30-01-2007, 11:29 PM
Hi Majikman

The clue is in the names of the controls, LP switch trips due to low pressure in the part of the system to which it is connected, HP switch trips to high pressure in the part of the system its connected to.
Sketch out a simple system and add some controls. Get a feeling for what state the refrgerant is in in various parts of the system, and see if you can picture what would make them trip.
To fix something you need to know how its parts works, so you can picture what would be the effect on the system if they stopped working.
Next time you complete an install, spend some time watching the system run, measure the temperatures and pressures, get a feel for how it works.
As for a book, get yourself a copy of Modern Refrigeration and Air Conditioning (from Rpw) and read all of it, pleanty of refrigeration stuff applies to Ac as well.
Oh and keep asking questions, the only dumb question is the one you don't ask:)

Cheers Jon

momo
31-01-2007, 12:39 AM
For all readers: I support P.Powell,MG Pony & monkey spanners opinions: get some theory training, practical training at a college (usually includes winding up lecturers as you do silly things:D & experiment) and then out on the road with experienced patient pro's then start earning your living when nobody is around to help ! :rolleyes::)
You will ALWAYS be learning from then on...
There are too many penny a job installers out there already: Many years ago Spain had "Pepe Goteras (drips) and Otilio (fat and lazy)" as kids comic characters of a botch'it and run plumber and assistant, I fear that they could well have moved to the realms of A/C in view of what's going on now.
Book: Try Refrigeration and Air conditioning Technology from Delmar Publishing W.C.Whitman & W.M.Johnson parts 1 & 3: basic, colorful, plenty of useful diagrams, charts, practical questions, tools etc perhaps a bit dated (I have the Spanish Paraninfo/Thomson Learning edition) and expensive. Or go to a technical bookstore in any University city and browse (take your credit card!):D:D

majikman
31-01-2007, 12:24 PM
Oh dear you are going to struggle..

LP trips for:
Low on gas
System blockage
Evap iced up/blocked
LP switch ****ed/set wrong

HP trips for:
Blocked condenser
High ambient temp
Overcharged
Wrong gas
HP switch ****ed/set wrong

erm.. that's all i can think of for now. Good luck, you're going to need it

Right guys..................

Perhaps I should have given you a bit more background info and wrded it better.

I have been in the buildings services industry for the past 3 years. the last year doing a/c.

I have attained both my CITB & C&G safe handling cards along with the 16th Edition. I also have completed both Mitsi & Daikin courses as well.

Most of my work in the last year has been install however I have done some service work. Mainly changing compressor's, finding and repairing leaks etc.etc. but my service experience is limited however i want to move over to the service side.

What i was lookig for were any reasons apart from the standard obvious ones Dr. Fleck stated. I was wondering if you experience guys had come across anything unusal that could trigger these trip outs ??????

Also with regards to the books, I was wondering if you guys carried anything with you that you could reference if need be ? I wasn't looking for a book to tell me how to do the basic stuff

so......................... let's start again !!!!!!

p_p
31-01-2007, 08:16 PM
Sorry if you were offended majikman but i still stick with my original reply, I hope you have got well away from that building services company and got yourself a position at a dedicated rac company, i think you will find it will help your learning and career progression. I worked for a b/s company, i left after 1 day when they told me i was on 24hr call for electric roller shutter doors (how s..t is that) I now run my own company.
All the best

paul

Dr._Fleck
31-01-2007, 10:28 PM
Why would you want to know the more uncommon reasons for LP/HP tripping? Are there any? All they are is pressure sensors. They don't have a bad day at the office and trip, or trip because they haven't had thier little window cleaned at the last service.

The reasons i've listed above are the problems you will come across when you start doing breakdowns.

You will need a good understanding of electricity to find faults, alot of people find this a stumbling block.

All the best Doc

monkey spanners
31-01-2007, 10:37 PM
Unusual reasons for trips

LP switch
Capiliary worn through and brazed up (blocked) by previous "engineer"
Chewed by dog.
Spring gone weak so tripping at too high a pressure.
Compressor oil gone waxy and blocking strainers (toshiba units on R22)
Unit in windy area in winter so cold that it trips on LP on startup.
Pipe work crossed with unit next to it, other unit off on overloads due to duff fan motor.

HP switch
Remains of kitten wraped around fan blade/motor.
Vibration eliminator collapsed internaly causing unit to cycle on start up until suction pressure lowered.
Compressor discharge pipe shot flat with shotgun:eek: (don't ask)
Clear plastic bag sucked onto condenser.
Condenser fan running backwards (duff capacitor, wired wrong, two of three phases to fan need swaping)
Fan blade loose on shaft.
Customer using unit to dry motorcycle gear:rolleyes:
Not removing plastic plug from new discharge valve just fitted:o
Spring gone weak causing contactor to chatter with the discharge pulses.

Cheers Jon

majikman
01-02-2007, 01:17 AM
Unusual reasons for trips

LP switch
Capiliary worn through and brazed up (blocked) by previous "engineer"
Chewed by dog.
Spring gone weak so tripping at too high a pressure.
Compressor oil gone waxy and blocking strainers (toshiba units on R22)
Unit in windy area in winter so cold that it trips on LP on startup.
Pipe work crossed with unit next to it, other unit off on overloads due to duff fan motor.

HP switch
Remains of kitten wraped around fan blade/motor.
Vibration eliminator collapsed internaly causing unit to cycle on start up until suction pressure lowered.
Compressor discharge pipe shot flat with shotgun:eek: (don't ask)
Clear plastic bag sucked onto condenser.
Condenser fan running backwards (duff capacitor, wired wrong, two of three phases to fan need swaping)
Fan blade loose on shaft.
Customer using unit to dry motorcycle gear:rolleyes:
Not removing plastic plug from new discharge valve just fitted:o
Spring gone weak causing contactor to chatter with the discharge pulses.

Cheers Jon

Cheers jon,

Some useful things to know there, some really out of the ordinary !!!!!!!

majikman
01-02-2007, 01:20 AM
Why would you want to know the more uncommon reasons for LP/HP tripping? Are there any? All they are is pressure sensors. They don't have a bad day at the office and trip, or trip because they haven't had thier little window cleaned at the last service.

And there was me thinking not all a/c guys were up there own a**e !!!!!!!

Seems I was wrong.

Do me a favour, if you haven't got anything helpful or constructive to add then don't bother. It only makes me waste time reading it !!!!

a1onetimeagain
01-02-2007, 01:40 AM
I don't often feel moved to post in a forum. I felt after getting banned for my first post as "a1onetime" maybe i should just sit back and watch/listen.

So at the risk of getting banned again, i'll say what i think most people are proberbly thinking.

"DR._FLECK, shut up you k**b and have a bit of respect for other peoples questions"

There have been "I know-it- alls" here before.

Adios

p_p
01-02-2007, 09:08 PM
Hi a1onetime(alias D...HEAD

May i suggest that you learn how to spell before posting anymore replies.
I have heard of the Dr and by all accounts a truly first class technician.
This site is for professional enginers to share knowledge and discuss the great career we have all chosen, and not for people who think they are to ask daft questions.
Look at the Dr's first reply, he gave majikman some tips and said he will struggle WHICH HE MOST DEFINATELY WILL.

THE END

majikman
01-02-2007, 09:21 PM
Okay lads can we not turn this into a slanging match.

I finally got the info I was after in the end so it's all good

!!!!!!!!!!!!

Obi Wan
01-02-2007, 09:48 PM
Gents or should I say ladies, Please!!!

I thought I stumbled on to the Big Brother website. Which one of you is Jade or Shilpa.

There are many reasons for HP and LP switches to trip, some are obvious some are not so obvious, but all can be diagnosed with generous helping of common sense.

I often speak to engineers on the phone and it amazes me at the lack of fault finding ability some engineers show.

A bad call will go something like this;

Caller: Help me Obi Wan Knobi, you are my only hope. My unit is tripping out on low pressure.
Me: OK. What pressure is it tripping out at?
Caller: I don’t know, I haven’t put my gauges on yet.
Me: Aaaaaaaaaa.

A good call will go something like;

Caller: Help me Obi Wan Knobi, you are my only hope. My unit is tripping out on low pressure. Can you confirm the pressure at which the LP should cut out at on this unit.
Me: (Ahh a professional – check model data) LP should trip at 0.3 bar and reset at 0.5 bar.
Caller: I am operating the unit in cooling mode, I have a gauge on the suction stop valve, but its reading above 5 bar when it trips.
Me: (look at the piping diagram) There is a strainer between the stop valve and the LP switch, can you see any frosting when the unit starts.
Caller: Yes
Me. Check the strainer, either it’s blocked or it’s collapsed.

Other reasons can be,
Systems are cross wired or piped.
Blocked liquid pipes (too much brazing material)
No nitrogen purge during installation (carbon on the inside of pipes blocking strainers and filters)
Dry joint on the PCB
Not wet ragging the replacement HP/LP switch.
Nitrogen in the system (exceeding maximum pressure during pressure testing)
OH and gas leaks.

Regards

Obi Wan:)

Dr._Fleck
02-02-2007, 03:01 PM
Thank you pp you are obviously a damn fine engineer like myself, we must meet up sometime, do they call it a 'meet' in forum language?


As for me being 'up my own a**e'... Well i suppose i have got rather a large self opinion. If the fridge trade wasn't populated(mainly) by so many unskilled idiots then i'd be put in my place, until then you'll have to endure me.. or until i get barred.

Happy call outs everyone i'm off to Scotland for the weekend.

The MG Pony
02-02-2007, 08:00 PM
Hmmm aren't we supposed to be mature adults here?

Or is AOL invading RE?

Come on now play nice, no need to go calling names and acting like a 15 year old having a hissy fit. We are all builders with our own unique strengths and weaknesses.

frank
02-02-2007, 09:36 PM
Unfortunately, I've decided to part edit some of the last posts, due to unnecessary language etc.

Hopefully, the posters involved will take on board the edits and calm down.

This is a forum where refrigeration engineers from all over the world visit to share knowledge and to discuss interests. What we don't want is uncontrolled rants or differences of opinion outside of the core interest, i.e. REFRIGERATION.

Lets get back to normality. :)

Josip
02-02-2007, 09:47 PM
He, Majikman :)

welcome to RE.


Hi guys,

New to the forums so hello there !!!

Just an easy one really. On splits and vrv's what would be the reasons the systems would trip out on high or low pressures ?????

I have mainly been involved in the installation side and I am now looking to move over to the service side so need a little info.

I have a basic ide but would like to know the common reasons !!!

Also does anyone have any reccomendations for books I could carry around with me on a day to day basis that cover general air con ????

Thanks

Scott

please take care to not post too heavy questions on Fridays;) ,

guys are under stress and need only a tiny spark....hope this will not come back to me:D

Best regards, Josip