Obstructed Capillary Tubes

[terrygoodrich]

I have been finding more cases recently of obstructed cap tubes on commercial equipment. All have been with R-134a or R-404a refrigerant. I don't know if it is the POE oil causing the problem. The obstruction is usually partial, causing high superheat. This often causes frosting of the evaporator and ultimately leads to compressor failure. I found a couple of threads relating to a similar problem on domestic refrigerators. The consensus for domestics was to dispose of the refrigerator and buy a new one. That isn't practical with more expensive commercial equipment. Is anyone else noticing these problems?

[Mark]

Hi terrygoodrich,welcome to RE
Had this problem a few times .I usually try clearing restriction with nitrogen (OFN)flushing or cutting back capillary tube.One other method is to islolate electrically, reclaim any refrigerant, unsweat suction from compressor,disconnect cap at drier and purge from either side of drier and up the disconnected suction into the coil.
Failing everything if accesible replace the whole capillary according to manufactures recommended length.

[chemi-cool]

Hi Terry,

The combination of R-134a + POE oil cleans everything from inside the copper tubes and the result is obstruction in the cap tube.

I used to do as Mark did but no more. always replacing the cap tube.
Sometimes, I would choose a bigger diameter one and work out the length.


Chemi

[terrygoodrich]

Replacing the cap tube is often a difficult task the way these cases are assembled. Why don't the filter-driers prevent whatever is fouling the cap tubes from getting in there in the first place?... and why don't the manufacturers use larger diameter tubes if that solves the problem? I have installed expansion valves on some ice cream cabinets that are particularly susceptible to compressor damage from high superheat. This isn't an easy task either! I just wanted to get a feel for the extent of the problem out there. I'm sure compressor manufacturers are feeling the pinch from compressor failures under warranty. That will fuel the fire for a solution. Thanks for the replies guys!

[frank]

Why don't the filter-driers prevent whatever is fouling the cap tubes from getting in there in the first place?...

With R134a it's the oil that waxes and blocks the capillary. No filter will prevent this.

[chemi-cool]

With R134a it's the oil that waxes and blocks the capillary

At what temp doe's it wax? Or is it happening all the time?

S***t refrigerant

Chemi

[frank]

Have a look at this old thread Chemi http://www.refrigeration-engineer.co...read.php?t=458

[chemi-cool]

There was life before I came

To be honest, I hated it the second time I've used it, Back in the last century.

Dont tell anybody, but I retrofit to R-12.

It works so much better

Chemi

[terrygoodrich]

I can't see how the refrigerant could cause the blockage. The solids must be coming from the oil or a combination of oil and moisture. The solids are being deposited in the capillary tube immediately after the filter-drier. It doesn't seem to matter what brand of filter is used. I suspect the solids are in solution and precipitate out as the refrigerant pressure and temperature drop through the cap tube. That is the only way they could get through the filter. Is there a chemist in the forum?

[chemi-cool]

Believe me, its the R-134a that causes all the problems

Chemi