How to tell if cap tube is too long/short?

[Duzter]

Hey everyone,

As I have been reading this forum for a long time now, a question has come to my mind.

How do know how long my cap tube should bee?
How can I tell from the running unit if the cap tube is too short or if it's too long?

I am used to working with TX valves, and have never worked with cap tubes before. So I am very interested in getting some hints and how-to's about the cap tube length or size.

Not a single one of my refrigeration books say anything about working with captubes. :shrug: All they write about is the TX valve and liquid injectors.


Thanks in advance.

Best Regards
Duzter

[EvoCarlos]

hey :)
form what said form this fourm 3m of 0.031" is a good starting place but if you unit pulls lots of vac then its probbly to long
most people try between 3-2.5m and have some good resaults :)

Gary Lloyd's cap tube rule (http://www.xtremesystems.org/forums/showthread.php?t=29694)
is very usfull as for load vs captube lenth

hope thats some help
but there will be other's with a diffrent approch

longer = lower lowside pressure and higher hiside pressure
shorter = higher lowside pressure and lower hiside pressure

but pressures change with given load so it can be anything from a range of pressures :)

[Moc]

Only way to tell your captube is good-sized is to measure the superheat and subcooling.
Superheat with a singlestage should be at load between 3-5K, Subcooling as low as possible. When you apply maximum load to your evap, Subcooling should not get higher than 3K. If it will, short the captube.
For a 11ccm+ unit 2,1m 0,8mm (0,031") captube is very good.

[Jack]

Its hard to guess exactly, because of several variables (compressor size, refrigerant, required cooling capacity, captube size).
Just as Moc said, measuring superheat is the way to go :up:

(@ Moc, "Subcooling should not get higher than 3K". That should probably be superheat instead of subcooling)

[n00b 0f l337]

Another less proper method is the "forced to hold" method.
Basically if you add refrigerant till the system till your load goal is held, then take a look to your compressor temp, condenser temp, and pressures you can quickly decide.
Pressures too high (discharge and compressor temp high), cut captube, this will lower pressures; basically your captubes too restrictive and your amount of charge needed is only holding because your forcing alot through.
Pressures really rather low? (Look for floodback at lower loads, condenser and system seem to be having a grand ol time?) You might be able to gain a few degrees by adding captube.

As you can see from there, it's almost no problems with running a shorter captube except you'll have a higher risk of floodback and a bit worse temps.

[teyber]

Only way to tell your captube is good-sized is to measure the superheat and subcooling.
Superheat with a singlestage should be at load between 3-5K, Subcooling as low as possible. When you apply maximum load to your evap, Subcooling should not get higher than 3K. If it will, short the captube.
For a 11ccm+ unit 2,1m 0,8mm (0,031") captube is very good.

[/thread] lol

[Duzter]

Sorry for not returning you answers guys. :down:

Many good responses, will take this into account when I finish my load tester and I'm able to load test it properly. :D

Thanks again.