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Abe
03-07-2004, 10:50 PM
Been looking at an Arneg Multi Deck......I am posing this question

I have always considered Gary's arguments about overcharging.........and I accept his philosophy, ie: dont use a full sight glass as an indicator

On this unit I am trying to apply his logic to this unit.......Sight Glass is bubbling.........Yes

I am not going to put more gas in.........Does not have a leak
back pressure before crank case is 70 PSI After I have adjusted to 50PSI

If I reduce it any further it frosts back right into the compressor

R404A

Head pressure is 175PSI
Air on 20 PSI

Air off........23 Psi

liquid line is ambient temp.........just a touch more, nothing significant


How can I tell if I got the charge right???

Gary
04-07-2004, 03:44 AM
I'm not familiar with that particular piece of equipment. Can you describe it?

What are the rest of the numbers? And specifically, what is the superheat at the TXV bulb?

Peter_1
04-07-2004, 08:08 AM
Aiyub,

Is the evaporator not frosted?

If ventilated, are all the fans running?

If fans are running, are all the bottom plates (air guidances) in the correct position so that air can only pass through the evaporator? Perhaps someone (another tech or the client after cleaning) replaced them in the wrong position. saw this fault many times.

In some units I know - if a multideck is that what I think what it is - there is sometimes in the perforated back some sort of air difuser (honey-comb structure) This blocks sometimes due to the dust.

How do adjust your BP? With the spindle on the TEV?

Air on/Air of are °F I presume.

What was the initial reason your client called you Aiyub? Is he having already longtimes problems or did this happened in the last days? Sometimes you can learn something from his story.

jan behnke
04-07-2004, 09:25 AM
First things first are you using the right gauge’s, suction pressure on 404a dependent on ambient in the shop is 4 to 5 bar, 404a runs at a higher head pressure than R22 liquid line should be warm to very warm, 20c air on 23c air off I think you have turned down the TEV to much, set it back to it’s original position, never look at the sight glass if you can help it, I always listen to the TEV to here if it’s short of gas.

Gary
04-07-2004, 09:55 AM
There is no such thing as a proper charging procedure. Such procedures always assume that everything else is working properly. We should make no such assumption. Checking and adjusting the charge should always be part of a comprehensive diagnostic procedure.

IOW, as always, we need the full set of temperature/pressure measurements.

Latte
04-07-2004, 10:01 AM
Hi Aiyub,
First of all can you confirm this whether this is an integral unit or has a seperate condensing unit.

I have unfortunatly worked on quite a few of these (Condensing unit types). Head pressure very low, should be 230-240psi ish. Back pressure also quite high.

Depends how much time you have to play with it. Persanally i would evacuate to check the charge for certain, might be difficult if on condensing unit, then check the orrifice in the expansion valve, all the ones i have worked on are fairly old and i have never had to adjust a valve usually it just requires a new filter and orifice, then change the drier, vac out and recharge. At least this way you know there should be no restriction or contaminants (Moisture ) in the system.

As peter said check the fans this can also couse problems and also do a pump down test on the pot if possible and check its not leaking internally.

Hope this helps

Regards

Raymond

PS just had another thought (I know very unusual on a sunday) do you know the history on the unit. You say it doesn't have a leak but that is not to say it hasn't had at some point and you never know which cowboys have worked on it in the past.

Abe
04-07-2004, 11:58 AM
Thank You all so much for your input. But here is the story. Yes it is Sunday, two kids, 10 and 7 years old waiting for me so I can take them to this tournament thing they have annually.

But they can wait..............

This is the story. I think a cowboy has worked on this unit.
I got to site, to provide a second opinion. Customer says the other engineer has condemmed the compressor.

Condensing Unit is: Prestcold PL 40X/0050-12

I found the weatherproof cover off, rain had fallen all over the unit, the cover protecting the compressor electrics had cracked, hence water inside the electric compartment of compressor.

I dried it all out, and found that one lead connecting two terminals on compressor thermister device had severed.

I went back next day when unit had dried out and started. Compressor started up and ran smoothly.


I notice case temp is high. Also sight glass is bubbling. I dont know if unit has had gas refills. Customer only acquired shop one month ago, so does not have history. I am not absolutely certain it has no leak.

This is when I did my pressure checks. I blew out condenser coil. I was unable to check superheat settings, because on Arneg Multi Deck. was too difficult to find the expansioin valve.


When I checked back pressure, it was 70 PSI ( After crankcase protector) I closed it to 40PSI, but starting frosting back........So I increased it to 50PSI, now frosting stops just short of compressor body.

I wanted to close expansion valve, ( increase superheat) to get down back pressure, but as I said, I didnt know how to get to the valve unless I took off all the stock........Something I didnt want to do.


When system goes into pump down, compressor takes a long time to pump down...........also liquid line , after the solonoid valve the liquid line starts frosting......( prob an inefficient solonid valve not closing down properly)


All the evap fans are running, I could not tell if the evaporator coil is frosting through.........

I will go back tomorrow and take further tests



It is a 4 meter unit..........Has two expansion valves. I know, I followed the pipe runs and it branches off.

So each expansion valve I presume serves a 2 metre run. System is pump down with one Solonoid valve only.

I took off the bottom base cover from first section. there are four evap fans for the first section and they are in vertical position. The evap coil is behind this. Do I have to remove all stock to get to Expansion valve???

Im thinking what else has been asked. The pipe run I think is around 7 metres. Condensing Unit is remote , outdoors.

It is 404A. The ambient of 20C I guessed that.......its not accurate. also I guessed the air off as 23C. The liquid line is not even blood temp.........it is just warm....I would have prefferred it to be hotter.

I think the Unit could do with topping up quite frankly..........but that high back pressure worries me.

As Rdocra points out............Expansion valves could do with new orifices................What size orifice would I need????

Peter_1
04-07-2004, 01:07 PM
That was what I meant with 'what's the story of the customer'

What I think Aiyub: wrong gas in the system or a mix from R404a with R134a or something like that.

For some cowboys, gas is gas whether it's R404a or R134a.
They charge with the bottle that's nearest to the door of the van.

I should evacuate the gas to an empty cylinder, vacuum a little bit and restart with new correct gas in the system.

Try to fill a little liquid in an empty bottle and look if the temperature corresponds with pressure. But it's sometimes due to the expensive labor hours cheaper to recharge it immediate.

So Gary, if you don't know what gas is inside the system, then you can't measure any pressure/temperatures correct because what refrigerant scale do you have to look?

It's sometimes difficult to service machines when others worked on an installation. Therefore, I always listen to what the client has to say but I never trust it and check for myself if it is or can be true what he/she is saying.

And even if your client is not a mechanic at all, sometimes in his story there can be found usefully elements to pinpoint the cause of the problem.

And it's sometimes hard to explain that you need to recharge a system to eliminate one possible cause. They sometimes think that you do this only so that you can charge a new and expensive gas filling.

To reach the TEV's, you will need to remove all the goods and the bottom plates.

If the TEV's are Danfoss ones, turn out the spindle complete and turn it back again 3 turns to 3.5 tunrs (every 1/2 turn is 1°C superheat, so 6 to 7DT superheat)

Are both TEV's the correct ones? You will need 2 x orifice 4.

Let us know what you have found Aiyub.

Peter

Gary
04-07-2004, 04:38 PM
This being a remote condensing unit, I assume it has a king valve at the receiver outlet, which can be tightly closed for pumpdown. That's where I would start for two reasons:

1. To see if the compressor valves are good. That may very well be the problem, as we are showing high load on the low side and low load on the high side, although this could also be TXV overfeed.

2. Once pumped down, shut off, and given a few minutes rest, the high side pressure should match the outdoor temperature, roughly indicating type of refrigerant and purity.

Yes, there are cowboys aka hacks everywhere, but I don't like to jump to that conclusion, either. I also politely listen to the customer. But mostly I let the machine do the talking. I don't like assumptions. I like measurements.

iceman007
04-07-2004, 05:58 PM
Aiyub

If it helps at all. The TEV on these units is normally located on the left hand side about half way up on the rear. To get at it you need to remove the shelves, and the plates at the bottom, which should enable you to slide out the rear panels and access the TEV. All the ones I work on have had Danfoss ones.

Best Wishes
James

TIGERDADDY
04-07-2004, 06:14 PM
I Dont Know Much About This Application, However I Do Know You Should Pump Down The System By Closeing The Liquil Line King Valve And Make Sure You Have Good Valves In The Compressor. Secondly, Some Of The Refrigerants We Have Today Are Blends And They Have To Be Charged As A Liquid And If Not They Lose There Propoerties. If The Refrigerant You Are Useing Is A Blend You May Want To Remove The Entire Charge (of Course If The Compressor Has Good Valves) And Pressurize The System With Nitrogen. Making Sure You Have All Refrigerant Out By Evacuating After Recovering You Will Want To Pressurize To The Max Limit With Nitrogen And Do A Standing Leak Test To Ensure You Dont Have Leaks. If A Blended Ref. Leaks Out As A Gas It Changes The Chemical Make-up. I Agree With Gary Gary's Methods He Has Has Good Advise . Let Me Know What You Find.

Tigerdaddy

Latte
04-07-2004, 07:35 PM
Hi Aiyub,
Well that condensing unit is a R404 unit.

The only way to check the orrifice sizes is to take the old one out and replace with the same (You just hope that someone hasn't just fitted whatever they had in the past).

Have known quite a few of these pots to go down, usually electrically though havn't had many letting by.

Do a pumpdown test if it pull and holds a vacuum then relcaim & check exp valves and change drier.
if the unit is fairly old and had a lot of work done i would say for definate that the filter in the orrifice is blocked or that the orrifice is burnt out for sure

Regards

Raymond

Peter_1
04-07-2004, 09:19 PM
Perhaps I misunderstood but how can an orifice be burned out?

Gwyn
04-07-2004, 09:36 PM
This system is either sort of gas (a lot) and thus causing a higher than normal suction pressure or possibly air in the system, first I would check for air and then if not air at least you will have checked the suction and head valves for 100% pumping etc.. As a quick way to remedy the problem the like the other guy says recover and re-charge the system and set the tev’s to factory setting this should at least get you a system that works then you can tweak from there… good luck.

Gwyn
04-07-2004, 09:37 PM
Perhaps I misunderstood but how can an orifice be burned out?
this seems a little bit strange?

Peter_1
04-07-2004, 09:44 PM
Aiyub,

Where can we send our invoices? :D

Gary
04-07-2004, 10:53 PM
Aiyub,

Where can we send our invoices? :D

Sending the invoices is easy. The hard part is getting paid. :D

Abe
05-07-2004, 10:26 PM
Im going back to site tomorrow............and Ill be closing this job, I may have to check expansion valves...........but I feel confident sorting this one out tomorrow

And I want to be paid as well, tomorrow............No sending invoices.........I want to see the colour of his money!!!

I will post a full report tomorrow

angryk
06-07-2004, 06:14 AM
Is the report going to sart with compressor pump down efficiency? Damn I'm curious what the outcome of this is.

frank
06-07-2004, 08:06 PM
This system is either sort of gas (a lot) and thus causing a higher than normal suction pressure

A shortage of refrigerant causes a HIGH back pressure ! :eek:

Am I missing something :confused:

Peter_1
06-07-2004, 09:17 PM
Didn't noticed this Frank. You're right.

But air in the system can also be correct but then you have very high discharge temperatures.
If I doubt about air, first thing I do is checking LP pressostat to see if it cuts out before atmospheric pressure.

Abe
06-07-2004, 10:25 PM
I promised a full report today......guess what, It was hot today and as usual all hell broke loose.....
I had to commission my brand new Mitshubishis today, First one kicked off.............second one..........Bloody condenser fan wouldnt start.......All the switching done through neutrals, so I spend best of afternoon troubleshooting
Why on earth should I have to " repair" brand spanking new equipement???
Dont the OEMS check before dispatching????

So, tomorrow morning back to the Arneg job...........so I will report 2 moro.

I went to a cold store breakdown this evening.........Talk about a cowboy job...........I will take a pic tomorrow and post, worst one Ive seen

frank
07-07-2004, 08:08 PM
Don't get me going on Mitsi's Abe :D

chemi-cool
07-07-2004, 08:21 PM
guess what, It was hot today :D

Hi Abe.

Was it 28C? :rolleyes:

Been spending three days in a plant room 42C ambient.
Outside was "only" 36C. What a relief it was to go out in the evening, didn't even switch the AC in the van

I guess "hot" is relative.

Chemi

frank
07-07-2004, 08:27 PM
didn't even switch the AC in the van

Now that would be a luxury in the UK :p

Abe
07-07-2004, 08:29 PM
I promised a full report.........Well I do have it........But right now, I am in pain......My left shoulder.....I went to the trade counter this morning......I told my freindly BSC ( Thats Behind Shop Counter Man) Not Batchelor of Science.........that I think I got a heart attack coming on............He guffawed.....He said dont be silly, fit young man like you

I pointed at my left arm you see........not my left shoulder !!

Anyway........Ive been working all afternoon on a cold store job.......I feel the pits now!! I got locked in the room.........I went for a last look see........this is after I had put away all my tools

Room had no Door Lock Safety Release.........I sat in room banging away for half hour.........No one came!"!!

Then I phoned my missus..........Thank God my mobile still worked from inside......( Sometimes they dont))

She rang around......I was thinking of dialing 999, had visions of fireman breaking in........

Then this guy opens up.........What you doing he says.........I heard lot of banging............UI thought you were fixing the fridge!!!!

I said nothing.............I came home
My shoulder still hurts..........

Later tonight I will post all my readings on Arneg!!!!!

Abe
07-07-2004, 08:37 PM
Frank,

About Mitsi.......our babe.......Tell me more!!
Ive only just met her........I need to know her sordid past..

My hearts breaking now........But she has stood me up.....Why is Love so blind???

Looks like I will have to give Miss Daikin a hard stare.........and motion to her to come over, so we can have a long slow dance in some dark corner"""

chemi-cool
07-07-2004, 08:42 PM
Never walk into any place before you make sure there is a way out!!

This should be the story of the year :D

Did you at least banged S.O.S? :D

Chemi :)

frank
07-07-2004, 09:06 PM
Last summer we fitted 3 Mitsi heat pump cassettes in a well know little place in Matlock Bath (it has a Wishing Well) without naming names.

Because the customer wanted to enclose the rear yard with a new roof next year we had to fit the condensing units really high up in the back yard. Anyways, we eventually came round to commissioning and, as always it was on a Friday afternoon. Number one went OK. Number 2 went OK. Number 3 ran smooth for a while and then suction pressure started to drop :eek: , head pressure went up and - bang, out on high limit.

So, as it was Friday and nearing PUB time, tools went away with a determination to return on Monday to sort it.

Have you ever had to deal with Mitsi Technical? - before I get slanderous I must say that they are the best bunch of humans that I have had the pleasure of knowing :D :D if you know what I mean. Have you tried this? - Yes, well have you tried this? - yes - what sort of engineer do you think I am? (Ar*ehole) - of course I've tried the rudimentally basic things and I think that it is a BLOCKAGE! Well, I'm not sure, have you tried this?

Patience is wearing thin now so we agree to have a new indoor cassette delivered as Mitsi think this is the cause as maybe someone in the factory may have been over generous with the solder on the distributor.

Scaffold down, (really awkward staircase and lots of Joe Public about, and return in a few days time at 6am (before the public arrive) to swap the cassette. Scaffold up, recharge the system, runs nice, think we have cracked it and then - bang - suction starts to drop, top condenser fan backs off, head pressure continues to rise and - hey presto - HP trips. Back to square one. To cut the story short, It was 6 weeks before we eventually got a new top half condenser delivered and we put up the scaffold once again, de-gassed, stripped the unit, took out the top half condenser, put in the new one, re-built, charged, switched on thought we had cracked it again only to watch the suction pressure start dropping again !! :mad:

At this stage Mitsi started to stop answering the phone and would not ring back as promised. Eventually traced it to one of the capillaries on the liquid line leaving the top condenser just prior to entering the tev. Mitsi technical Support - we salute you (bunch of To**ers)

To cap it all, they tried to charge us for the cassette and the top condenser :)

We Love Daikin, We Love Daikin, We Love Daikin, We Love Daikin

Gary
07-07-2004, 09:21 PM
Technical support has the same problems we have here. They can't see the system, and there isn't enough information provided. What is needed is a full set of temperature measurements, but for some obscure reason everyone prefers to guess at what's wrong and swap parts until it works. People will waste hours, days, or even weeks in an effort to avoid measuring temps.

frank
07-07-2004, 10:06 PM
Oh we gave them temps Gary - they just didn't listen!. And as all we could do was request assistance under warranty, we had to go with their decisions until we snapped and demanded action. This little project cost many hundreds of £'s that was not recovered from Mitsubishi. They just sit behind a desk and talk on the phone not bothered about our embarassment with the customer and each time they send out a part they think is at fault (after all they are the experts) - jesh- they issue an invoice to cover and fight about it later. NOT one of my favourite companies :mad:

Gary
07-07-2004, 10:28 PM
Unfortunately, that's typical. I have spent (wasted) a lot of time arguing with "experts" from the factory.

Feeze
24-10-2004, 01:02 PM
I promised a full report.........Well

Later tonight I will post all my readings on Arneg!!!!!
I know that this is an old post but
Aiyub, I am curious about your outstanding report.

Latte
24-10-2004, 06:24 PM
Hi Guys,

I appreciate that all you guys in technical support need as much info as possible. Do you have a specific form that you have to fill in each time somebody rings.

Obviously, you will want to know model,serial, Gas type, pressures and fault.
Can somebody post a list of ALL the info you would like iff possible then people could print it off and fill it in BEFORE ringing you

Regards

Raymond

snake
26-11-2007, 06:29 PM
When are we as an industy going to stop talking about PSi and Bar and talk in real terms - degrees C.
If you all used pressure as a C then we would not have to ask what refrigeant and we could easily compare pressures to actual temperatures in a store or process. The refrigerant is almost almost irelavent if we know what the temperatures are.

endurance
26-11-2007, 08:27 PM
to get the charge right,there should be no more bubbles on the sight glass.
good luck
endurance

PoodleHeadMikey
01-12-2007, 04:31 PM
Assuming that you know the compressor to be good; it pumps down and holds, etc. And that the coils are both clean al the way through, the fans are clean and running the right direction and speed, and the condenser air and evap air temps are within the 'normal' design range of the equipment - Then:

Check the liquid line subcooling - you want about 5-10 degrees F.

Set the superheat at the evaps to about 12-15 F.

Go back and check the subcooling and make sure it is still OK.

What would be handy to see here is a full set of numbers. All pressures and temps and conditions listed. Like the list on a start-up sheet?

PHM
--------

Gary
01-12-2007, 05:17 PM
When the subcooling is low and/or bubbles in the sight glass, this indicates that there is insufficient refrigerant in the high side of the system... but that doesn't necessarily mean the system is short of refrigerant.

Low superheat/floodback tells us that there is too much refrigerant in the low side of the system... so now we know where the missing refrigerant is.

Abe seems to be missing in action. Perhaps he has forgotten how it all turned out. After all, this happened 3 years ago... and he isn't getting any younger.

MadMax
12-12-2007, 03:54 AM
R134a is ****house. havent worked with 404. 410a is over-rated.. takes too long to get going