PDA

View Full Version : Obstructed Capillary Tubes



terrygoodrich
08-03-2005, 04:34 PM
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? :confused:

Mark
08-03-2005, 06:00 PM
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
08-03-2005, 07:11 PM
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
10-03-2005, 01:43 AM
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. :rolleyes: Thanks for the replies guys!

frank
10-03-2005, 01:47 PM
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
10-03-2005, 04:10 PM
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 :mad:

Chemi :)

frank
10-03-2005, 05:12 PM
Have a look at this old thread Chemi http://www.refrigeration-engineer.com/forums/showthread.php?t=458

chemi-cool
10-03-2005, 08:56 PM
There was life before I came :D

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
17-03-2005, 04:20 AM
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? :eek:

chemi-cool
17-03-2005, 03:48 PM
Believe me, its the R-134a that causes all the problems ;)

Chemi :)