You know, checking superheat can be a tricky thing. Its been my experience that when the suction line is over 1 1/2 inches the outside temp of the pipe is just not accurate enough for superheat check. Your on the job you need a fix now. What I would do is valve down the txv all the way then open it 1/4 turn and see how the system runs. Slowly open the txv from there. What we know for sure is your slugging the compressor. Good luck.
I did valve off the suction line a little at a time open and closed, foaming was still present, and since there was no oil pressure drop from start up through settling in, it would give me the impression that I am not slugging the compressor. Since the liquid refrigerant mixing with the oil should affect the oil pressure, and again, the oil pressure stays stable at about 40 psig, (+ or - 1 or 2 pounds when compressor is loading or unloading), I don't believe that I am slugging the compressor.
I also wrap my thermocouple with a piece of rubber strap, then electrical tape that for a fully insulated and tight thermocouple contact to the refrigerant line. Since the rubber strap wraps around the refrigerant line as well as the thermocouple, the reading should be pretty close since the pipe is well insulated at the point of contact for the thermocouple. The pipe and thermocouple are also not affected by any ambient conditions...
1). Here is a silly question: Are you measuring the cooling coil outlet's superheat using two thermocouples (inlet/outlet); or are you using a single thermocouple at outlet and (at same place) measuring pressure using a Scrader valve?
2). For two temperature method, I like Fluke Model 52 with their 80PK-8 clamp thermocouples. I like that better than the thermocouples with the bead at the end.
3). For temp/pressure method: use JB Industries superheat gauge http://www.jbind.com/pdf/JB_2011_catalog.pdf
4). If compressor isn't running steadily for 15-20 minutes, it is hard to measure superheat.
5). If cooling coil outlet's superheat is "high" (20's deg F), then refrigerant flow is "low" and oil stays in cooling coil.
6). Looked at Sporlan catalog, and your TXV is externally equalized. So there should be a small tube from the cooling coil outlet to the TXV body. If tube is clogged with dirt/oil, then no "pressure input" to the TXV. That might be why the superheat stays high (even when TXV is adjusted)
I am monitoring temps at coil outlet, and near compressor. The fluke clamps won't work on lines larger than 7/8" I think, and the suction line on this circuit is 1 7/8" I think. That is why I wrap the thermocouple with the rubber strap. It allows me to get a good, tight, insulated contact on the refrigerant line. I actually prefer doing that over using the clamp on just because of the insulation factor at the point that I am trying to read the refrigerant temp.
I followed all the instruction from the Copeland tech support on checking and setting the superheat.
The thing that really confused me was even when the suction service valve was closed more than 75%, I still had the foaming issue (I was not checking oil pressures at the time so I do not know how that was affected), but unit did not shut off on oil pressure switch and I had the low pressure switch bypassed.
I had no problems keeping the compressor running.
This unit is also a constant volume system for our clean suite. It is usually running under light load conditions, and I am limited on how cold I can get this clean room suite as we can only produce our drugs under specific temp and R/H conditions. Causing the suite to go outside of those parameters would require a halt to production, which does not look favorably upon me...ha ha.
I was able to get SH to adjust as described in my very first post, so I doubt that the eq line is clogged, I just have problems getting 10 more degrees of SH from the outlet of the coil to the compressor which is what I was told from the Copeland tech, which is why I was checking line temps at the compressor as well as the coil outlet.
I gave the wrong model number for the "big" Fluke Pipe Clamp thermocouple
Fluke 80PK-10 Pipe Clamp Temperature Probe
For pipe diameters: 1.25 to 2.5-Inch
0.25 to 1.38-Inch
There is no problem with mixing mineral oil and POE oil. In fact, with certain refrigerant blends that are approved for use with mineral oil is is recommended that if oil return problems occur that adding a percentage of POE to the system will enhance the return of the mineral oil to the compressors.
Originally Posted by trouble time
See page 3 in the attached DuPont retrofit guidlines.