Phase-change frustration

[gkiing]

Well after much time and effort, I finally finished my first homemade direct die (ive owned and regassed a mach II before, but nothing entirely diy). I did a triple evac; vacummed for an hour then purged with r290, vacuumed for another hour and purged with r290, then vacuumed for another hour and a bit. I static charged the system to 40psi (with r290) and switched it on. The pressures were around 10" low and 170 high. The evap wasnt cold yet so I added some more r290 bit by bit and brought the pressures up to 0psi low, 205psi high. The evap got cold after about 15 or 20 minutes, but the lowest I got was -9.2 at 14c ambient (outside here), and the cap tube and suction line were frosted about 6" up.

It sounded like there was gas hissing through the evap block, not liquid. After I turned the unit off i heard hissing in the evap, not the usual sputter. With the system off the pressures equalized at 76psi low/80psi high. the system is UNINSULATED.

my consists of:
-tecumseh aeb1380axa compressor; 1/4hp LBP (made for r12, but has POE oil in it).

-6x6x4.5" 3 pass condenser with a 60cfm fan (the condenser didnt even feel warm when the compressor was running)

-smallish filter drier

-6' 0.026" cap tube

-maze style evaporator made with a drill press, 2x2x1"

-1/4" id flexible suction line

i know it's a rant but im just frustrated that it wont work. Ive regassed 3 mach units to 404a without trouble (would 404a be better??).

[Redwolf]

Sounds like either the cap tube has something in it or it is too long. Could also possibly be restrictive evap. That 1/4" suction line isn't helping either.

[gkiing]

I would think it would get cooler than -9c, my captube or evap is probably clogged. The captube isin't too long since its frosting on the captube, if anything it could be lengthened. I'll put on a 3/8" hose and change the captube tomorrow, maybe that will help :\

Any of the resident experts care to help?

Btw redwolf, do you have any more info on your autocascade? Is it really "turn it on and run"?

[Redwolf]

Yep its plug in play :)
http://teampuss.com/forums/viewforum.php?f=46

[rhino56]

sorry to be off topic but what is team puss? that just sounds disturbing in like everyway possible. lol

[gkiing]

teampuss owns you :banana4:

haven't found an answer to my problem yet... :( :( :(

[Redwolf]

To bad I don't live closer to the border anymore

[gkiing]

well i've changed the fan for a 100cfm model and I'm going to check the captube for restrictions in the morining. Otherwise, its probably the evaporator.

Is it a possibility that no liquid was ever getting into the evap? Or is it just very restrictive and thats why its only -9c (at 0psi propane should be -42!!)

the compressor is rated for a 234 watt load at -31.6C

[chilly1]

You need 110 inches of .028 capillary tube The pressure should be aroung 2 to 4 inches ov vacume running unloaded. You need more cap tube PM me and I'll send it your way on monday...
You may have a problem with the little amount of mineral oin in the system and poe added may cause it to thicken and sluge up the evaporator.

EDIT: The condenser you have is a six pass.. if it is like those I have here.

[m0nk33y]

your capillary tubing length is should be right, there could possibly be restriction in capillary tubbing.

[chilly1]

Post the piping inlet and outlet temperatures of the condenser. And the suction line temp.

[gkiing]

I've got lots of .026 captube, but I think its a little too small for direct die. I also need a new hose because the one im using now I think leaks (it's a rubber yellow jakcet pressure control hose).

This is an r12 compressor BUT the oil has been changed to POE at the factory. It says on the label POE oil but i know that cant be right because it is an r12 compressor.

I also need to make a U bend before the suction as I realized I forgot it and don't want liquid slugging, even tho i dont think I'll get any.

Yes the condenser is a six pass its one of the ones you got from usa manufacturing.

I'll put up some pics tomorrow.
I'm going to have a fun time brazing because The unit is in a wooden case . Thing is I had the whole system working before, then I changed the cap tube and put it in the case and now everythings messed (another reason its probably the captube).

[chilly1]

You may have inadvertantly pinched the end of teh cap tube during assemby. Is your cap tube wrapped around teh suction line. this will give you better temps than inside .

[gkiing]

Yes the cap tube is wrapped around the suction line, I couldn't do it inside the suction because of the 90degree bend on one end.

[rhino56]

teampuss owns you :banana4:

haven't found an answer to my problem yet... :( :( :(
like what does that name mean though?
P.U.S.S
i know what my mind says it means, but im hoping its something like

people under stressful situations or posting up stupid stuff
sorry i cant help with the topic though. :toast:

[tictac]

Yes the cap tube is wrapped around the suction line, I couldn't do it inside the suction because of the 90degree bend on one end.

How aboout 2 Cap tube to that evaporator head.... :toast:

[gkiing]

what would be the benefit of 2 cap tubes? Either way I'll have to re-braze the evap block, unless im sure that the blockage isint at the entrance of teh captube to the evap (i think it may have melted shut).

[gkiing]

Well, heres a little update:

I disconnected the evap and captube from the system and flushed it with some dry n2 at 250psi, whatever was blocking it must have gotten jostled out because around 225psi the nitrogen started hissing out the captube. I reconnected the captube, evap, suction line and charged it to about a 2" vacuum on the low side, and ~200psig on the high side. With the evap uninsulated and nothing on it it got to -43.5C, and there was frost 6" up the cap tube and all the way back on the suction line to about 4" from the compressor.

Is it normal to have frost all the way back to the compressor? I know that the frost on my captube means that I should lengthen it a bit, but I think it will be ok after I put it on a heatload. The first pull down of the unit took about 5 mins, I turned it off and the presures equalized at 92PSIG. I started it up again and it only took 30s to get to -43.5c.

What are some common pressures for the system to be at when its off and equalized? I know that my machII was around 80psi.

I know that someone said that prommys operate best at 4" of mercury on the low side, should I let some gas out of my system? It's at around 2" now.

[chilly1]

The frost is normal for an unloaded system. Charge to 4" and take teh temperatures and pressures and post them...

[gkiing]

What temperatures should I take? I'll let some gas out so it's 4"low. I think I may get colder temps once i insulate it tomorrow.

[tictac]

what is ambient temp there ?

[gkiing]

well, when I was charging it I believe it was around 18C (i was outside). The temps may go up a bit when I bring it inside, but I'll try to tune it when its around room temp (22c) outside.. I don't really want to charge with propane indoors, ive had a previous bad experience that resulted in r414b in my face (lucky I was wearing a plastic face shield, but my whole basement had to be aired out for ages to get it out)

The problem I have is when disconnecting the gauges somer refrigerant always escapes, is there any way to avoid this?

[gkiing]

I think i've got a leak. When I checked it last night it was at 92psi off, and this morning its at 65. I checked all the brazed points for leaks with soap and water and couldn't find any, so it must be in one of the connections with the hose and flare washer. Is it possible it's the rubber hose itself?

[chilly1]

Shouldn't be a leak in the hose.. But maybe...

[chilly1]

Remove the insulation pressurize it and put it under water. Was the unit recently run when you got the 95 psi? It may be the refrigerant is mixing with the oil this will lower the pressure in teh system as the oil dissolves into the oil. when the oil is warm it will hold less...

[gkiing]

I let all the propane out of it, vacuumed it, and put in 110psi of propane. After about 5 mins my gauges read around 103psi, then after another ten around 100psi. I can't find the leak, and ive looked EVERYWHERE. I'm going to get a buddy of mine to put some dryn2 in it and see if I can find it then.

[chilly1]

Well the propand will mix verty well with the oil. Enough to drop 30 or 40 psi. Make sure tyou evac well before adding nitrogen as the propane in teh oil will mess with the proessures let it stand at 150psi for a 24 hour period it should change less than 10 psi.

[chilly1]

Remember to remove your guages and put a cap onit being careful not to lose much nitrogen.

[gkiing]

ok, will do. I just dissassembled the wooden case it was in so I can check the brazing joins more carefully, even though I really doubt thats the cause of the leak.

[chilly1]

Does the performance drop?

[gkiing]

Im not sure.. I didn't start it up after the static pressure had dropped. Should I try that first? I could give it a quick suck and charge.

[chilly1]

Did you take the static pressure before running it the first time and not running it the second time? I would run it and get a set of readings before recharge.

[gkiing]

I took the static pressure after it had been run the second time and hit -43.5, and after the system had equalized. I'm going to take the whole thing apart tomorrow and put it in a better case, I've had it with it right now and I can't find the leak. I'm going to have to get a stainless hose, I'm almost positive that my leak is through the rubber in the hose (its going down around 1psi an hour).

The last thing I did was vacuum the unit to 29" mercury, leave my gauges closed and connected, and now the pressure a few horus later is around 25" of mercury. I think im just going to redesign the whole system and get rid of those damned flare connections.

[Redwolf]

You can always braze the flare connections... if the tubing is metal.

[gkiing]

It's a rubber hose :\ I'm going to call the home depot and see if they carry S.S hose.

[chilly1]

hey have plastic coated stainless hose.

[gkiing]

I hope so, but I'm in canada so the home depot might be different :\

[chilly1]

I think the gas lines used on a gas water heater are the same there. I have seen some canadian equipment and I remember a stainless gas pipe.

[JSU]

i though that home depot was only in the us. go figure......

[Redwolf]

Canadian Tire :) Use to live in WhiteRock/Surrey

[gkiing]

Already been there, they don't have s.s hose..

[gkiing]

I'm having it tested with dry N2 to check if its got a leak, we put 150psig in it and couldn't hear any leaks or find them with soap and water, so wish me luck that it's still at that in 24 hours. If it is, im going to have to have a little celebration. That leak (or not?) has been driving me insane, i'm hoping it was just the propane being absorbed by the POE oil..

[m0nk33y]

yea i had a similiar problem with my system, the system was charged with r-290 and it would keep on losing pressure... i checked for leaks and didn't find any

[gkiing]

Did you system performace decrease at all? I think that this oil just sucks up the propane, and I know propane is usually used for oil return because its so miscible with the oil and helps carry it.

It's currently holding 150psi.. keeping my fingres crossed :banana:

[m0nk33y]

wouldn't it be better to pull a vacuum so the oil can't absorb??? you are testing for leaks? not pressurizing?

[gkiing]

I'm testing for leaks right now with the dry nitrogen. I've had the system up and running before but I never checked it for leaks so I thought I should to be sure, and then I checked with propane and found a phantom leak that I cant find, so now im using nitrogen to be sure. I will charge with probably 10psi of propane and the rest r22 when im done. I have to let it sit for 24hrs to be sure that theres no leaks.

[m0nk33y]

oil will absorb some nitrogen

[gkiing]

Nitrogen is imiscible (will not mix) with POE oil.

[m0nk33y]

well i seen halloween use nitrogen in his cascade to test, and the oil would absorb it. Pressure drop

[chilly1]

Actually only a few psi will get absorbed...

[gkiing]

So nitrogen is miscible in oil?

[m0nk33y]

better to pull vacuum, nothing gets absorb.. if you plan to test for leaks

[gkiing]

Well, it wouldn't hold a vacuum, but I suspect that the refrigerant that had been absorbed by the oil was coming back out of the oil in the vacuum and making it rise. It has been at around 148psi with dry nitrogen for nearly 24hours now (from 150), so I suspect that it has no leaks. If it did im sure the pressure would have dropped.

[chilly1]

So nitrogen is miscible in oil?
Basically it isn't. a little may be absorbed but not really.

[gkiing]

When I filled it the pressure was 150psi and then in the night it got cooler and it went to 147psi. Now I brought the unit back in because it was raining outside and it's at about 151psi. It hasn't leaked over 48hours, so It must have been the propane being absorbed in the oil, that oil just sucks it up.

[chilly1]

Yes. Propane is very misicible with all the oils we use in refrigeration this is what makes it so good to use as an oil carrying agent in cascades.