cap tube question

[CBRAKO]

when putting a condensing unit on a cap tube with a reciever must you remove the reciever for it to work right. or doesnt it matter. thanks for the replies

I am pretty sure the reciever is for a TXV system and it must be removed if you are going to a cap tube...but I am just a newbee!! GL

[TGoodrich]

Hey I printed & read that article on the theory of cap tube operation. I've gotta admit, I had a lot to learn. I always thought a cap tube was just a simple restriction... well it is simple I guess, but the way it works is far from simple! And I thought I had it all figured out... (Never too old to learn)

Thanks Icemeister!!!

[engineerdave]

when putting a condensing unit on a cap tube with a reciever must you remove the reciever for it to work right. or doesnt it matter. thanks for the replies

This may sound like a dumb question, but why would you convert it? What metering device are you using now and why re-engineer the machine instead of just fixing whatever the current problem is?

[lugnut]

Very interesting thread. This "receiver" scenario can be seen if you have a situation like I currently have. I have a True reach in freezer with a low slightly low suction pressure (9 psi, instead of desired 15 psi)) and I have two possible explantions for it.

#1. There is a cap tube partial clog.

#2. Someone before me has installed a Sporlan c052 liquid line drier filter just before the cap tube. I believe this oversized drier is a mistake and I believe it is behaving as a 5 cubic inch receiver. The net effect of this reciever on this cap system is too 'gain' heat (reduce subcooling) in the receiver, thus the net effect is to starve the evaporator. Hence a slightly low suction pressure.

Im not looking for advice here, as I know how to determine which is the real problem when I return to work Monday. I just wanted to share my views on how a receiver might be detrimental to a cap tube design.

By the way, I've been reading icemeister's posts all weekend. He da man !

[TGoodrich]

If you added a larger filter-drier you would need to increase the refrigerant charge to compensate for the greater volume. I'm sure you had already considered that. Many of these small systems come with the little spun copper driers and, if the system is opened for any reason, they are better replaced by an 032-CapT which is a bit larger. I usually adjust the charge by checking for proper superheat after the cooler or freezer is down in the normal operating temp range.

[fl_dude]

I'm with "engineerdave" here. Why change a more efficent metering device, for a device that is known to clog up easily? Rather like some one else said, warm R134a just a tad to much, and you have a waxed up cap tube. my advice, stick with the TXV.

[Wheelbaron]

Get rid of the R 134-A
Seriously, I junk the stuff all the time.
Industry standard, what a load....

[Poodle Head Mikey]

Of course - maybe I am an idiot too. <g>

Liquid flows through a cap tube based on the pressure difference across the cap tube. The End. (almost <g>) Now; more subcooling Will slightly increase the refrigerating effect because less latent heat will be needed to cool the refrigerant to evap temp, but how much? Five degrees worth of the specific heat of the refrigerant?

No matter where the liquid comes from - if the pressure drop is the same - the flow will be the same.

If refrigerant will migrate through the cap tube from a receiver - why wouldn't migrate from a condenser?

And even beyond the above - I am sure I have installed a receiver condensing unit onto a cap tube system when that was all that was available. And no negative incident resulted.

[jinu117]

The only negative effect would have been higher static pressure in the scenario. Work harder you compressor!
Somethingto worry about without receiver is critical charge. Once you start charging too much, you effectively start to reduce condensing surface area.
Maybe it's time you put receiver in system if you expect varying capacity need and temperature.
One thing that helps is to faciliate some SLHX functionality to reduce this problem to give more consistent operation.

I do use cap tubing ALL the time as I have consumer geared product I produce here on my side and using cap tubing right unfortunately has been something of an art. You can't have moisture in it, any change in sizing will mean you are back to scratch, etc. (but the size of these systems don't leave me much option but to cap tube it...)
Just stick to TXV if you can help it (just because I use it doesn't mean I like it)

[rowen]

The cap tube meters the liquid and it needs to be liquid. The compressor provides the pressure to keep the liquid present at the entrance of the captube and if you have mixed vapor/liquid then it ain't gonna work. Thats it in a nut shell. Old school refrigeration on flash gas.

Ray..............................

[cjcargo]

when putting a condensing unit on a cap tube with a reciever must you remove the reciever for it to work right. or doesnt it matter. thanks for the replies

Must be removed. The unit may work for awhile, but useually causes the compressor to overheat. I've read that If the reciever is used on cap tube systems it has to be relocated between the compressor and condenser. I can't find any information on why this may be nessesary.

[jinu117]

It's actually quite simple.
The space in receiver plays huge role for cap tubing system.
The receiver adds additional amount of refrigerant required for cap tubing to have enough liquid to operate.
In critically charged system (which cap tubing is), this surmounts not critically charged system.
Since the condensing unit's operating condition changes (as well as evaporator) what will happen is varying amount of liquid residing in receiver which might starve cap tube at a time, or overflood it and compressor can be hurting not receiving enough cooling from returning gas/working too hard with way overcharged system.
Too big of filter/drier on highside can also cause similar problem.

[PaysonHVAC]

Yikes. Is this going to be one of those things that everyone has a different opinion on?

However after reading this I think I may remove the receiver the next time I get a new condenser for a cap tube reach in.


I just started a new job and am doing low temp again. I installed two condenser sections in two McCall reach in coolers that someone else ordered the parts for before i started.

They both came with RECEIVERS. And that's what i installed.

The only good news, is one of them McCall units had a TXV

But the one with the cap tube was a real biatch to adjust the charge. But I was back there towday, two days later to work on something else and it's holding temp juct fine.
But if I ever open that system for another repair, I'll bypass that receiver. Heck. It caused me to add another Lb of R134a that i therwise would not have needed.



Oh, here's the new unit with the receiver.

[air2spare]

Get rid of the R 134-A
Seriously, I junk the stuff all the time.
Industry standard, what a load....

...the 134a in your vehicle?

[Poodle Head Mikey]

It started because I let the dealer do a 12-to-134 conversion on a 1993 Dodge. They then put ten or twelve compressors on it in two months and it never did cool as well.

I went to 414 and it's been fine ever since.

[n8ies]

[QUOTE=lugnut;1521040]Very interesting thread. This "receiver" scenario can be seen if you have a situation like I currently have.

I believe this oversized drier is a mistake and I believe it is behaving as a 5 cubic inch receiver. The net effect of this reciever on this cap system is too 'gain' heat (reduce subcooling) in the receiver, thus the net effect is to starve the evaporator. Hence a slightly low suction pressure.

Just point the outlet of the drier down, lower than the inlet and the "receiver effect" will go away. Otherwise you have to add enough refrigerant to fill the drier to the point where there will be a liquid seal at the outlet before proper operation is realized.

tom

[sumdumguy]

so then would'nt there be a mathamatical equation as to the length and id for the flash obtained. if you wanted to install say a looped coil to chill@ tail gating party