Air in system

[lunapepin]

Hi,
My first post and a big problem.
I Have air in a parallel compressors system, no way of recovering refrigerant, a lot of refrigerant, and not too much diff of levels betwen evaporators and condensators, wich is the better way of stop breaking compressors and High Pressure with less R-22 loss?
It looks like a trivia, but it isnt

[Gary]

How do you know there is air in the system?

[Mobbsy]

Lunapepin, I'm somewhat intrigued as to how the air entered the system, I don't think you are discussing a freezer on R22 with a S.S.T of -41 celsius or below which would therefore run in a vacum (when you say parallel do you mean a rack or multistage system); so has the air entered through poor pressure testing i.e. part of the system pressure tested with nitrogen at a presurre greater then the live side.
What is the system running pressures? and what is the standing pressure at the ambient temperature of the day?
What is a lot of refrigerant, because there is no maximum cut off point, which is deemed to be so great that one does not have to recover, that would be environmentally and professionally iresponsible.

If you begin to elaborate a little more on how you have reached your final conclusion, I will aid in you in your quest to rid yourself of these nasty non-condensibles.

[750 Valve]

Lunapepin, I'm somewhat intrigued as to how the air entered the system

You'd be amazed mate, I once did a call to a supermarket and the mgr hands me a stem of a solenoid valve and tells me he found it at the plantroom door and there is heaps of hissing going on in there. I went in and found an MT rack tripped on HP (cycling on HP actually). Turned out that an unloader energised and popped the stem off the unloader/solenoid assembly, it was a Copeland reed compressor. Condenser had a gutfull of air in it.

How it entered.....

When comp energised it sucked air straight down the unloader stem as it was less resistance than opening the suction reed valve in the comp valveplate. When it tripped on HP it p!ssed gas out of it.

I ended up bleeding air off the condenser inlet (all supermarkets here have a schraeder at the highest point in the system - discharge inlet to condenser) and directed it thru a guage line onto a hand towel from the lunchroom until I found traces of oil starting to appear on the hand towel.

Got the system up and running and saved the stock, then repeated the process under nice cool ambients and a good off time to let anymore air rise to the condenser. New drier cores and an oil analysis and we were away.

[lunapepin]

Thanks for so interesting answers, I’ll try to give you more information, I’m not the refrigeration expert but got some experience managing maintenance but the contractors have a good technical expertise.
I’m talking about a rack of 4 Copeland semi-hermetic discuss compressors, we star looking for a reason because in a short time broke the same compressor (No.1), when replace it, then another compressor (No.3) broke valves and burned, while replacing this 2nd., the technician in charge detected a differential of pressure between condenser and the rack, (that don’t suppose to be ok), and that when the three compressor are working the system goes to high pressure, then, they proceed to purge air from the system at the condenser. But there isn’t a big differential of levels between condenser and evaporators so that all the air in system can be purge from the condenser; we’re locking for a higher place to purge.
More data is a MT rack, estimate charge 1,200lbs. on R-22, nine years working, actually 3 compressor on place but 3 working because HP when starts.
We presume as possible cause of air in system is, so much time changing expansion valves, making annual maintenance (whish include oil replacement), valves wear and leak into system by valves while repairing compressors.

Apreciate your help

[nike123]

Still, you did not posted any measurement which confirm air in system.

Check pressure of condenser against temperature of air blowing true condenser while system idle and high and low idle pressure is stabilized and equalized for some time.
Compare that with refrigerant P/T diagram.

[Grizzly]

Hi lunapepin.
I sincerely hope you find someone who knows what they are doing and soon!
I realise that you would not know any better and possibly the Dominican republic.
Does not have to comply with the same sort of codes of practise that we all do.
But you talking about 1200lbs of R22 being purged of Air.
Makes me think that your technicians don't know what they are doing.
Any fridge engineer or even their apprentice will know that the 2 cannot nor do not mix.
For lots of reasons.
But the several of the main ones are..
You cannot condense air therefore system pressures will rocket and serious damage may be a consequence of air in a system.
Also with air there is moisture, moisture freezes and blocks the free flow of the refrigerant also can produce very nasty acids.
Which contribute to severe motor burn outs.
I could continue but I feel that it may be easier if you just take my advise and seek further advise.
Simply put.
what you describe is a disaster to the environment, to you or your employer financially. ( the energy consumption must be huge)
And to any Engineer a mechanical disaster.
Grizzly

[lunapepin]

At condenser it has 218 PSI and at rack manometers 363psi. Now 30 and 406 at the rack with 3/4 compressors working

[Brian_UK]

:eek: Stand

w e l l

b a c k,

it's going to blow :eek:

[lunapepin]

What i'm looking for is a way of get the air out of system without refrigerant loss. If there is one way

[Gary]

I would suspect a restriction between the rack and the condenser. If the systems are hot gas defrost, there may be a pressure regulating valve in the common discharge line which should be bypassed if no coils are in defrost mode. Even in defrost mode, the pressure difference across the regulator should only be about 20-25 psi.

[lunapepin]

Thanks Gary, we're going to check, specialy at oil receiver, beside its a resistanses defrost system

[Gary]

... a resistanses defrost system

I don't know what that means. :confused:

[lunapepin]

I don't know what that means. :confused:
Sorry, electric defrost

[Mobbsy]

How it entered.....

When comp energised it sucked air straight down the unloader stem as it was less resistance than opening the suction reed valve in the comp valveplate. When it tripped on HP it p!ssed gas out of it.



Nice example 750, I will use that one with the young blokes. The main reason I was intrigued in this particular case though was to ascertain if there is actually air in the sytem.

[Mobbsy]

At condenser it has 218 PSI and at rack manometers 363psi. Now 30 and 406 at the rack with 3/4 compressors working

400 psig at the rack, it's no wonder your bending valves on your compressors, imagine the discharge temperature lunapepin. There are several points of discussion which you have mentioned that are of concern, please keep in mind that non-condensables within a vapour comoprression system do not accumulate at the physically highest point, similiar to that of a hydronic system, they accumulate at the top of the condenser and to a lesser extent the vapour space of the receiver.

To answer one of your questions it is not o.k to have such a large pressure differential 218 and 363 on the high side. Lunapepin there could be a restriction within the discharge line, I doubt it's at your oil seperator, somebody didn't leave a spanner in one of the new compressors did they. In all seriousness you need to describe the configuration of your discharge line, any three way valves, check valves e.t.c.

It may be best as Grizzly pointed out that you seek some local additional advice, a number of points you have made are of concern for both the plant and the plant owners, particularly the compressors burning out, because they will continue to do so unless some positive action is taken. I'm sure you and your team are doing all possible, but it sounds like you have exhausted all options immediately available to you.
I wouldn't be bypassing the high pressure control either, becuase if your running at a S.D.T of 154 farenheit that H.P has a screwdriver in it.

I have also included a link to the Australian and New Zealand refrigerant handling code which you may find interesting
http://www.arctick.org/cop.php

[lunapepin]

Thanks a lot, Mobbsy

[JohnSamsa]

Hi everybody, One should check that indeed the discharge service valves are full open on the compressor as the man stated they were fixing one compressor on the fly! Or even a discharge check valve! Something makes this situation complicated if you want. What I say is step back, take another look and for god’s sake keep it simple! The laws of physics just don't change! ó¿ó

John

[andywill]

I tend to agree with Gary, there is a major restriction between the rack and the condenser. You should be looking for a jammed "Non Return Valve" or even a restriction in the oil separator. I personally have had to bypass an oil separator (as a temporary measure) to get a rack back online and save the stock. I have to assume that your rack has got isolation valves on the discharge lines and if so this should allow you to fit test points (schrader valves) after a check valve (if fitted) and after the oil separator. You should be able to determine the blockage from this. Good luck cos you need to set the HP Switches back to what they were ASAP.

[Mobbsy]

Thanks a lot, Mobbsy

Another site you might be interested in http://library.thinkquest.org/12596/dalton.html

This site explains the law of physics which applies to Daltons law

Daltons Law: 'In a mixture of gases, the total pressure is the sum of the pressures exerted by the individual gases in the mixture, if they occupied the vessel alone'.
This particular law is indicitive of non-condensables present within a vapour compression system.