Cascade HX temps gone south..

[C-BuZz]

Hi,

Well I finished my cascade & it was running beautifully for 6hrs straight. Then HX temps died completely. I can barely get low side past 0psig regardless of charge. Keeps pulling a vacuume..

Things i've tried.
Replaced Filter/drier/captube/compressor... Still the same :(

I've now got a 1.5hp rotary on the first stage but its doing exactly the same thing as the last 1Hp roatry..

The only thing I havent replaced is the HX.

Which leads me to beleive there is a blockage somewhere in the HX..

I was getting -50c HX out before running for 6hrs straight, now I cant even get -10c / 0psig.

Can I see a show of hands who thinks my HX is blocked? Or as to the reason why my HX temps took a nose dive?

Any input much appreciated.

Thanks

C-BuZz

[Gray Mole]

Strange problem, but there's a few things that could cause it.

A blockage could be an issue, whether junk in the system getting into your captube/tev or moisture yeah.

The placement of the filter shouldn't be an issue in the 'warm' side of the cascade so filter freezing shouldn't be it either.

If your Low stage is too heavily charged or it's blocking up on the discharge side, then the high pressure can cause a high load and that can hit your HX hard if it's going beyond what your captube/tev is tuned for.

So if you could post ALL of your temps and pressures in the system, both Low and High stages, low and high pressures, and discharge, return, and evap temps all 'round, maybe there's something we could spot to help you find the problem.

Cheers

Gray

[C-BuZz]

Strange problem, but there's a few things that could cause it.

A blockage could be an issue, whether junk in the system getting into your captube/tev or moisture yeah.

The placement of the filter shouldn't be an issue in the 'warm' side of the cascade so filter freezing shouldn't be it either.

If your Low stage is too heavily charged or it's blocking up on the discharge side, then the high pressure can cause a high load and that can hit your HX hard if it's going beyond what your captube/tev is tuned for.

So if you could post ALL of your temps and pressures in the system, both Low and High stages, low and high pressures, and discharge, return, and evap temps all 'round, maybe there's something we could spot to help you find the problem.

Cheers

Gray


Thanks for your input.

The system was running fine for 6hrs & to suddenly loose temps like that has got me totally baffled & I have changed everything but the HX, & I really dont want to do that as it's all foamed & boxed so i'll have to start from scratch.

Before the problem occured pressures where fine. High 130psig, low side 15hg. Was holding load extremely well to.

Now I can pump the high side up to 200psig & the low side still pulls a vaccume of 10hg. It does still freeze back to the compressor but only when I pump way to much refrigerant into it. Temps are -10c/-15c HX out @ 200psig. Temps are the same @ 130psig/150psig/180psig/200psig...

Before they where -50c/130psig/15hg.

Second stage is not even running.

C-BuZz

[Gray Mole]

If that's the case then yeah, got to be some kind of blockage.

It's pretty rare you'd have enough junk in your HX to block things up, but have you purged while assembling the High stage?

It's not likely that there's enough to completely block the HX itself, but the captube or TEV valve is a distinct possiblity.

Also, what are you using to vacuum the system? Proper pump, or 2 compressors or something?

Is it a cap cascade or do you have a TEV? (sorry if I missed it if you already said) and have you tried replacing it?

I'm sure you'll find it, but both cap and TEV can be sensitive to junk it the system, and cap can be really sensitive to moisture as well.

Gray

[C-BuZz]

I think moisture could cause symptoms like this, however, if there was moisture in the system, why did it run for such a long time without any issues?

Low side pressures are acting quite eratic & not normal.. after a tripple evac when I first charge the system with a basic static charge of 50psig before switching it on. Normally low side pulls straight down to 30hg. But it only pulls to 20hg. Then I proceed to fill through the low side all the way to 200psig high & the low side does not go above 10hg.

When adding R290 I see the needle jumping quite eratically for a few seconds then it stabelises @ 10HG.

Thx

C-BuZz

[Gray Mole]

Ah cool, if you've gotten some erratic results as you charge with more 290, then I'd say it's disturbing the blockage momentarily.

When you add more gas to the stage and the discharge pressure increases, the suction pressure should always follow that and increase.

If it's not it quite definitely a partial blockage especially if you've already changed the compressor to test for it.

Like I said, it's very rare that with the size of the tubes in a HX that you could have enough junk to start blocking it up, but it's possible if not purging while brazing.

Moisure usually only get's the captube blocked, and normally it only get's you after it's been running. If it's happening even from the start after it's warmed up again, I'd say something's in your cap or HX blocking it.

Not fully blocking, as then you'd be pulling full compressor vacuum, but a partial blockage yeah.

If you could, pull out the gas, disconnect the HX, and blast it out with a gallo gun or high pressure nitrogen to see if you get a pile of black junk out of it. Do it in reverse from the way it's piped into the system 'backwards pressure' which should force anything out if it's stuck in there.

Cheers

Gray

[C-BuZz]

If that's the case then yeah, got to be some kind of blockage.

It's pretty rare you'd have enough junk in your HX to block things up, but have you purged while assembling the High stage?

It's not likely that there's enough to completely block the HX itself, but the captube or TEV valve is a distinct possiblity.

Also, what are you using to vacuum the system? Proper pump, or 2 compressors or something?

Is it a cap cascade or do you have a TEV? (sorry if I missed it if you already said) and have you tried replacing it?

I'm sure you'll find it, but both cap and TEV can be sensitive to junk it the system, and cap can be really sensitive to moisture as well.

Gray

I can purge through the high side with R290 & it flows freely out of the low side like there is no blockage at all :confused: Almost with no restriction whatsoever which makes it all the more frustrating.

If there was moisture in the system, there would have to be a lot of it.. What would be the best way to check this?

Using 3M of .031mm captube.

[Gray Mole]

Oh yeah, and after you blast out the HX in reverse I'd still recommend you replace the captube again.

However, personally I think that's far too long a captube for your system.

Even on my small cascade (1/2HP High, 1/3HP Low stage compressors) I used 5.5' of .031" captube to make sure I had the capacity on the High stage.

3m of .031" only gives around 200w of natural capacity and if you have rotaries and all that in there, you may struggle to get it to hold the load of the system when running with a load on the Low stage.

That's totally up to you for later on, but it's what I normally do.

The REALLY weak link if you don't purge while brazing is going to be between the filter and the captube. If you don't purge specifically on that point, you'll have crud right there where it's going to do the most harm. Blocking a filter with junk in the system can happen if you don't purge but it's not as common, but it doesn't take much stuff to block the captube entrance so a little more care in that spot while brazing is absolutely critical.

Cheers

Gray

[C-BuZz]

Ah cool, if you've gotten some erratic results as you charge with more 290, then I'd say it's disturbing the blockage momentarily.

When you add more gas to the stage and the discharge pressure increases, the suction pressure should always follow that and increase.

If it's not it quite definitely a partial blockage especially if you've already changed the compressor to test for it.


Its definately not following the high side pressures like it should.

Before I was able to charge to 130psig/15hg no problems. If it added more refrigerant the low side would increase as expected, & more freezback to the compressor.

Now I can charge all the way up to 200psig & low side remains at around 10hg give or take. It does freezback to the compressor but NOT all the way like it should (& did before). The freezback does not change no matter how much refrigerant I add, wich would certianly indicate a blockage in the HX somewhere as i've already replaced the captube & filter.

I didnt purge while brazing unfortunately.

THx for the captube tip. I'll shorten it. But I must say it was doing a fine job of holding the load of my 146 @ 2.78Ghz/1.75v core temps where -35c LOADED.


C-BuZz

[jinu117]

Cap tubing seems to be blocked from all sympton as Gray mentioned. I suggest just replacing it since it only is going to hx and is easier than changing evap one.

[C-BuZz]

Cap tubing seems to be blocked from all sympton as Gray mentioned. I suggest just replacing it since it only is going to hx and is easier than changing evap one.

Hi jinu117,

I just replaced the entire captube (brand new captube) including the filter :confused:

Still exhibiting the same symptoms.

The only thing I havent replaced in stage 1 is the HX.

C-BuZz

[Gray Mole]

yeah I've been noticing some are having decent results with longer captube on cascades, but I definitely noticed on my Rotary cascade that captube just wasn't cutting it on load, and I ended up switching to TEV to get high capacity with the extra heat from the rotary compressors.

Ah well, backflushing the HX may just get the stuff out for you and worth a try before replacing it :)

Gray

[jinu117]

Wierd....? Maybe there is residue of unwanted stuff floating around blocking the cap tube...? If there is enough crud in HX, I could see how that might be the case.
I second Gray's suggestion :)

[C-BuZz]

yeah I've been noticing some are having decent results with longer captube on cascades, but I definitely noticed on my Rotary cascade that captube just wasn't cutting it on load, and I ended up switching to TEV to get high capacity with the extra heat from the rotary compressors.

Ah well, backflushing the HX may just get the stuff out for you and worth a try before replacing it :)

Gray

Hey thx for the heads up. Going to replace the HX tomorrow & see how I go.

The system held an awesome load & that's just straight R290 in both stages. I didnt even get the chance to add CO2 to the second stage before the temps died on the first stage.

Here is the bad boy around 90% complete. System now has 1.5hp rotary compressor on stage 1.

And as you can see, i've already boxed/sealed the HX, so i'll have to start from scratch :(
C-BuZz

[johann]

I agree with Gray, 3m 0.031 is a bit too long

I use 2.6-2.75 on normal singles and the heatload on this is more than that. I would use 2.5m at most.

Cascade looks great!

[C-BuZz]

I agree with Gray, 3m 0.031 is a bit too long

I use 2.6-2.75 on normal singles and the heatload on this is more than that. I would use 2.5m at most.

Cascade looks great!

thx, i'll start with 2.7m & adjust if needed.

C-BuZz

[wdrzal]

post a pic and did you use ,purge gas,vacuum pump.

i/m not clear on this point did the second compressor do the same from the start or after it ran awhile. did you every run very high pressures?

on the removed compressor did you check for a burn out,acidic oil or compression, failed valves.


my intial guess is partial blockage water or dirt.

probably not hx but dont rip it out you can flow gas thru to test it.

[C-BuZz]

post a pic and did you use ,purge gas,vacuum pump.

i/m not clear on this point did the second compressor do the same from the start or after it ran awhile. did you every run very high pressures?

on the removed compressor did you check for a burn out,acidic oil or compression, failed valves.


my intial guess is partial blockage water or dirt.

probably not hx but dont rip it out you can flow gas thru to test it.

Hi Wdrzal,

I didnt purge HX while assembling unfortunately. The second compressor did exactly the same thing from the second I switched it on. Pulled a 20HG vacuume where it should have been easily pulling 30hg vacuume, as there was hardly any refrigerant in the system, just a basic static charge of 50psig. THe second compressor oil seems cler & fine. Pressures never exceeded 200psig high side.

Edit: I can purge through the high side & gas comes out the low side as if there is no blockage at all... It freely flows from high to low unrestricted (or so it appears)..

When I static charge after an evac through the high side, the low side pressures increase almost instantly...

C-BuZz

[_HL4E_HalfLife_]

I see one thing no one here has mentioned as of yet :eek:

Has ur thermometer probe come loose or has moved from where it should be to get a proper temp reading?

[jinu117]

I see one thing no one here has mentioned as of yet :eek:

Has ur thermometer probe come loose or has moved from where it should be to get a proper temp reading?


Errr.. PT? :)
20hg vacuum.... isn't what you will see on most working system.

[kayl]

I see one thing no one here has mentioned as of yet :eek:
Has ur thermometer probe come loose or has moved from where it should be to get a proper temp reading?

i mentioned tht when he first had the problem, along with a long list of other things. THis is a tough one, hope you sort it soon cbuzz.
Last time we spoke almost another -100c member before the problem arose hey.
Ya get it sorted soon I hope.:toast:

[C-BuZz]

Errr.. PT? :)
20hg vacuum.... isn't what you will see on most working system.

I've now replaced the entire first stage, including the condenser as I cracked it heh.. & didnt want any possible flaws in the system.

Edit, Yes I purged everythign this time while assembling! When I purged the HX, heaps of black soot flew out :)

C-BuZz

[jinu117]

I've now replaced the entire first stage, including the condenser as I cracked it heh.. & didnt want any possible flaws in the system.

Edit, Yes I purged everythign this time while assembling! When I purged the HX, heaps of black soot flew out :)

C-BuZz

Ah.... so you were keep blocking cap tubing over and over -_-;
Good luck man :)

[wdrzal]

If you built that rig without a using a purge gas you minds well scrap it. your problems will be never ending. Even if you install filter they will block evently,especially if you use refrigerants that are solvent in nature.

you can buy flush and install liquid line and suction line filters but you'll never get it clean totally.

[C-BuZz]

If you built that rig without a using a purge gas you minds well scrap it. your problems will be never ending. Even if you install filter they will block evently,especially if you use refrigerants that are solvent in nature.

you can buy flush and install liquid line and suction line filters but you'll never get it clean totally.

Noted & Thx to all who helped troubleshoot.

System is now up & running fine. Pressures are back to normal 130psig/15hg -50c HX out :)

C-BuZz

[kayl]

well done.:toast:
propane runs low with big condenser hey.