oil and txv clogging

[friocold2008]

I was reading in a refrigeration manual that mineral oil used in refrigeration systems can create some kind of solid ("wax") that accumulates at the neddle of the TXV, and eventually could reduce or completely block the refrigerant flow. If true, this could be the explanation to the high superheat readings that I experienced in a low temp R-22 refrigeration system during a failure of the oil separator: we did not realize that the hermetic type oil separator float valve was clogged, and added oil to rise low oil level at reservoir and compressor crankcase. Now I guess that both the originally circulating oil and that unnecessarily added oil could have traveled up to the evaporator and cause the waxing at the TXV. Have someone experienced a similar problem before ?

[tony--1]

yes lots ov time .
if the oil system is working ok now .
heat up the valves and hope that the extra oil goes back to the pack .
good luck .

[lowcool]

i put it down to a build up around the pin stopping bellow moving freely in the tx valve etc.heat did move it subsequently i chased moisture,but still should have changed the oil!!

[chemi-cool]

Mineral oil have no wax in it and works fine to -40°C.

What you describe is oil mixed with water.

The only way to over come it, is to recover all the refrigerant through a large drier. Take all the oil out and wash the system with a cleaner, put new oil in, new driers and recharge the refrigerant back through a new drier.

Any other short cut, and you can work on this pack for the rest of you refrigeration life.

[bill1983]

we used to experience this type of problem with hot gas defrost systems on low temp cases/coldrooms. On pack systems the solution was to fit wax filters in the suction line and replace them twice per year. Likewise with the liquid filters.
I only see it now on systems where the oil has been contaminated, either with moisture or due to overheating causing the oil to start breaking down. Replacing the oil and flushing the system usually clears it, otherwise several filter replacements follow. The time taken for both is around the same. However with the proactive method this can take place during respectable daylight hours. With the filter method, this usually takes place during the wee hours when you have been called out, often around 3 in the morning.
your problem sounds more like oil logging in the evaporator, reducing the heat transfer surface of the coil and causing the txv to underfeed. pumping the system down several times should help to reduce the problem; of course monitoring the oil level and removing the excess as the resevoir level builds up.

[Silhouette]

"Waxing" only occurs if the oil is overheated, if your compressor discharge lines are not above 120*c then this is not the issue you are having! Water or dirt in a system can cause the oil to thicken and clog up the separator needle valve, giving the symptoms you describe. REMOVE THE OIL! Clean the separator float assembly and recharge with fresh oil, clean all the compressor sump oil filters and recharge the compressors with new oil and you should be trouble free!

[lowcool]

what is the cause for sticking reversing valves in racs if its not this wax like substance?
i remember seeing this thirty years ago on r12 & r22

[joe magee]

I see wax in tx valves with low temp r22. I usually heat the vale and change out the driers. Some of the stores are changing the mineral oil to poe. The only problem is you will be changing driers for awhile due to it's great cleaning ability.
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