mixing cap tube and TXV
Have a customer that has a Randell prep table with a TXV for the cold pan and a cap tube for the lower cabinet. each section has a stat and LLSV. The complaint is insufficient cooling in the lower section. All signs point to a restricted cap tube.
I was always told that you cannot use a cap tube with a receiver and you cannot mix a cap tube with a TXV in the same system. Apparently the factory has done both here. Is there any reason I can't/shouldn't install a txv in place of the cap tube?
SH and SC and other data?
I don't see a problem with an externally equalized TXV as long as the suction piping does not allow either valve to be influenced by the other valve.
I'm glad you posted this one. I'd almost forgotten about the cap tube TEV mix on those units.
This is another example of the cheapening of an otherwise decent unit. Too bad.
While the capillary tube/receiver setup like that does refrigerate, the cap tube loses its innate self regulating ability which normally comes from the variations of liquid subcooling with changes in load or conditions.
Another reason not to use a receiver with a capillary tube is when done in the field, most systems are grossly overcharged and the compressor suffers or dies from repeated flooded starts. A captube system often has a small accumulator to compensate for flooded starts, but it's generally sized for a system without a receiver.
I think Randell has the flooded start problem covered with their use of a liquid line solenoid valve and thermostat. Essentially, the base evaporator(s) are pumped down during the off cycle, so no flooded start.
I would still opt for a TEV if faced with replacement of the cap tube. The coil is fairly easy to adapt to. Like Lynn said, go with an externally equalized TEV. The TEV will give you much better performance in the base section too.
I've worked on them before and they worked fine.
Can't say as I remember the unit having a receiver though.
Have you pulled the charge and weighed the correct amount in yet?
If You Can Dodge A Wrench You Can Dodge A Ball
I have worked on many of these units. They use tev's now and every time I run into a older one with a restricted cap tube I install a tev instead. I think they use a 1/4 ton internal equalized straight threw. I have never had a problem after converting one, in fact they cool so much better. I have done this on old delfield prep tables as well. I would put in a tev.