liquid line sight glass mystery

[austech]

Hi all
I have witnessed an unusual white substance appear in the liquid line sight glass of a 150 kilowatt commercial air conditioning unit. The sight glass is positioned 3 inches after the liquid solenoid and 6 inches before the expansion valve. When the unit is running it is fine, the sight glass is clear. As soon as the unit cycles off or unit is shut down the white haze will instantly appear on the inside of the glass. It appears crystalline, translucent and seems to be about 1 millimetre thick. I do not believe it is moisture. Can anyone shed some light on this?

[Brian_UK]

When the unit shuts down the solenoid valve closes and the continued suction pressure will suck the liquid out and as it changes to vapour the temperature will drop instantly.

It is possible that any oil in the line is being transferred to the glass surface.

[aeb200]

are you sure it isn't gas boiling off?
when the solenoid shuts, the unit will pump down and any liquid present in the pipe will quickly boil off - lots of tiny white bubbles???.

[Peter_1]

WELCOME.

We call it in Belgium 'mayonaise', (mostly not seen in sight glasses) but I don't know the correct English name for it (it can also be tartaarsaus)

[NoNickName]

Oil in liquid emulsion?
That's what mayonnaise is, after all...

[Argus]

WELCOME.

We call it in Belgium 'mayonaise', (mostly not seen in sight glasses) but I don't know the correct English name for it (it can also be tartaarsaus)

Usually with frittes, I think Peter.

But seriously, Brian has it, I think.
I always situated sight glasses after the liquid line service valve, but before any components, so it was not subject to periodic evacuation. Over time this can lead to a discolouration on the inside of the glass.

.
________
Second-generation Taurus

[Johnny Rod]

Sounds like a bit of oil, though if the moisture level in the refrigerant is a bit high then when it boils away like this at low temp it can be cloudy with snowflakes.

[austech]

Thanks for all feedback

I thought that it might be moisture as any moisture in the system when operating tends to accumulate within the expansion valve and may quickly dissipate when the unit cycles off and solenoid closes. There is turbulence as the liquid level diminishes during pump down, can be seen through the "frosted" glass. This part seems okay. Ususally in smaller systems the moisture would block the TX valve orifice but this is operating well (large EX very large openings). It wouldn't seem to be excessive oil circulation because it is clear when running. The system had been evacuated and recharged new driers etc. initially. Upon recommisioning that is when I noticed this phenomenon so I changed drier cores with ultra high moisture capacity type again and injected an additive called Thawzone (Highside Chemicals) and the problem was still there. If it was moisture I am sure this would get rid of it. Did an oil acidity test and that was okay. Hmmmm.... its all too bizarre.

[Johnny Rod]

Thawzone is basically antifreeze for fridges but it would prevent freezing up. The only way to check for moisture (other than colour-inidcating sight glass) is sample it and have it tested. What refrigerant is it? I find (my experience in the lab) that HFCs go cloudy with only a little dissolved oil a lot more easily than HCFCs, even when they're dry.

Check moisture for peace of mind, otherwise sounds like not much to worry about as whatever it is isn't impacting operation.

[Andy T]

is it the filter dryer breaking up I would change it.

[Andy T]

Just read the post you made later.I still think it's the original dryer.But the oil is mixed with the deposit.Change the oil a few times to remove it, if you can.And then change the site glass

[DeB]

There is a refrigerant in Australia used as an R12 replacement. One of its constituents is ethanol. Before charging, the refrigerant bottle needs to be shaken, otherwise the ethanol does not mix properly with the refrigerant and settles in the bottom. Each successive charging of the cylinder, causes an excessive build up of ethanol. When this "over ethanoled" refrigerant is put into a charging cylinder, you can often see a milky substance on the glass of the charging cylinder. As you have added thawzone which I think is basically methanol it may have compounded the problem.The system may have had previous bad moisture problems and successive technicians have added anti freeze and the excess antifreeze combined with the "diluted moisture" is causing the problem. Charge removal coupled with drier change and oil change and a long evacuation period may fix the problem.Sorry about long-winded explanation.

[herefishy]

A sightglass six inches before the expansion valve? Mind you that I have done that for diagnostic purposes in problematic systems, but have never regularly utilized a sightglass at such a location as a regular method of service.

Is there a sightglass at the condenser receiver outlet (typical installation) that perhaps doesn't manifest this observation? If so, I would ignore it.

What is the history of the equipment? If it has experienced many surgeries or improper service (sightglass downstream of the PDS sounds suspect), perhaps a pump-down, re-locate SG, change the drier, and evacuate would be called for. If after this service there is still concern - an additional drier change wouldn't hurt.

During some experimentation - I have observed vaporizing refrigerant in a translucent vessel (system in operation) and the result is merely a fog.

The device is called a "LIQUID" indicator, not a "VAPOR" indicator.


JMTCW

Cheers!

[Richard A]

Hello, all, just joined.

What you are seeing is from the soldiering/welding. The glass became etched. If you saw glass that floated up on the beach after a few weeks it is hazy until you put it in water and then its clear as being new.

Who ever welded possibly used a flux or overheated the fitting.

Im very sure of this problem, my first year as an apprentance I messed up about six of them brazing 1-1/8 sight glasses into systems and my boss made me change them out.

Rich

[Brian]

I've seen this mytery before. 2-years ago I changed a system over from R22 to R29 the same thing happened. The compressor oil sightglass looked like a lavalamp. It's down to the properties of the refrigerant. Miscibility... the compressor failed shortly after.

I wrote a detailed report on the problem but the customer insisted on using the refrigerant!!

Dohhh

[US Iceman]

I'm sort of a late comer to the discussion, but the problem sounds a whole lot like oil in suspension.

Since the site glass is downstream of the solenoid valve, the liquid is flashing off during the pump down cycle. Unfortunately, oil will not boil at the temperatures normally encountered in refrigeration systems.

So, as the liquid line pressure decreases the oil will tend to stick together and concentrate. This is similar to the floc test for wax in refrigeration oil if my memory still works.

If there is no acid or water present in the refrigerant and the systems readings all look OK, I wouldn't worry about it.

To be on the safe side, you might enquire with the manufacturer of the oil to see what the dilution effects of the oil & refrigerant are at various pressures and temperatures.

[Brian]

Hello,

Just to clarify, this effect happened when the chiller plant was running at full load, not on pump down!

[US Iceman]

Just to clarify, this effect happened when the chiller plant was running at full load, not on pump down!

That does certainly seem like a miscibility/solubility problem. The proof is that the compressor failed shortly after the conversion.

It's oil dilution with reduced viscosity.

[John Wood]

I think it is hydrofluoric acid in the system, this has attacked the glass in the sightglass. At first it will only show up when the sightglass is empty, if I am right it will get worse as time goes on. Try doing an acid test on the system, then take it from there...

[donato]

has anyone heard about sludge (peter_1)?; it did apear in one case in the metal maze of a filter/drier core after changing the oil. It was completely full with the stuff.
looked like mayonaise yes, but brown (indeed this was Betekom belgium!) mind boggling that time, but now I know: mayonaise! Peter , were you there perhaps?