View Full Version : Help! Not enough pressure too much vacuum
hey, I am in the process of chargin my dd system with r507. I static charged it to 30psi then let it run. The pressure wont go above 175psi (not enough to condense my r507) and the low side is about 5psi.... is this because there is too much charge? When I let some out the pressure went down :(
craig588
08-05-2004, 07:18 PM
Maybe you need a little more?
Is the compressor strong enough?
Is it leak free?
Its a 1/4hp low temp r22 compressor. It was leak tested with nitrogen @ 230+ psi. Iam thinking about adding more but why is there no vacuum on the low side?
craig588
08-05-2004, 07:33 PM
I have no idea, the only phase change systems I have built have just been made through experimentation, I don't quite know all of the theories behind it. I was just guessing in the previous post hoping it might have given you an idea.
I added more and the pressure went up to 175 and the low side is 10psi :( . Btw I let out some earlier and the pressure went to 150~
i think the pressure has more to do with temp of room
or if the cap tube is too restrictive may increase it.
also with out a load the discharge pressure will increase.
eg for me
using r290 on a 16c day discharge will be 150PSIG then on a 24c room temp pressure increases to 175PSIG (low about 6PSIG)
but what pressures you should have with r507 i cant say sorry
sorry kayl, I tried r290 also and nothing will create lower temps for me..... For r507 you need to be @ 180psi with 80f ambient to condense. I wasnt hitting that. With r290 I hit 150psi (no matter how much I put in :( ) and no cold temps either. This is bad. Any ideas anyone????
could a lack of oil be the problem??? Also with r290 why wasnt I getting anything cold at 150psi???
Redwolf
08-05-2004, 10:55 PM
507 problem....
With 80F ambient your condensing pressure will be more around 225 - 250psig.
Sounds like either your flooding, ie captube isn't restictive enough
or leaky discharge valves.
Whats your system temps/pressures when it gets to the lowest it can go?
Everything stays about the same evap was 72f when ambient is 75~ . Condensor does not go above ambient but about 1inch of discharge from is hot. Why can my compressor do 175 psi+?????
(its not a r507 b/c the compressor should be able to handle 250psi easily. btw 80f on the pt is 180psi ;) . )
cap tube is 12ft~ of .028.
this is realy disapointing.... before I was able to get 225psi and a 7-hg vacuum. (something around there)
Epsilon
08-06-2004, 01:33 AM
captube seems a bit long
10ft is enough
Gary Lloyd
08-06-2004, 03:22 AM
Quit trying to achieve what you imagine to be the right high side pressure. It is whatever it is, according to load, room temp, condenser sizing and airflow, and has little to do with refrigerant charge. You cannot charge a system by high side pressure.
Charge it until the suction line is frosted and the compressor is warm. If the bottom of the compressor is cold, you have too much refrigerant. This will get it in the ballpark.
gary its not that, its the fact that no matter how much I put it it wont go over 175psi which isnt enough to condense. The pressure stays at around 150 on the high side and the added refrigeratn only affects the low side. so id have 150/40.
no matter how much gas I put in there no frost shows up :(
pythagoras
08-06-2004, 09:06 AM
Have you got this sorted yet JSU? Unless you have a leak the pressure must increase as you add more refrigerant. Have you noticed the pressure dropping with the unit switched off?
Regards
John.
oc_nightmare
08-06-2004, 09:50 AM
that's happening to me too. dont matter the gas charge i put in the system when i turn the compressor on the discharge line doesnt get hot and the succion remains at the temp it was b4... when i switch the compressor off the system pressure remains in vacuum like if it had nothing in it.
the system was leak tested at 240psi for 12h and no leak was found.... where the hell is the gas goin?:mad:
pythagoras
08-06-2004, 10:09 AM
Sounds like the same thing that happens to a car when the piston rings start to go and you lose compression:mad:
Regards
John.
HawainPanda
08-06-2004, 12:09 PM
how can u know if ur compressors faulty?
HawainPanda
08-06-2004, 12:10 PM
i mean even if u do hear it running, how do u know its actually compressing how much its supposed to?
hatemi
08-06-2004, 12:17 PM
From the preasures...Just like in car engines you have to test the preasures...In engine you put the gauge in place of spark plug and in compressors in high/low side...
Pcice, I guess we have the same problem :( this compressor is new. o well :( I guess I have to order 4 compressors now. 3x 1/2hp roatries, 1 for vacuum pump 1 for this project (want to finish it) and 1 for a cascade when I finish this system (I got payed today and think iam gong for cascade.) and one 3/4hp rotarie for the cascade........
btw how much heat do you need to damage a compressor? I was brazing a joint and the torch was hitting the top of the compressor for a little while. When I sotpped brazing the compressor was prolly about 300f on that spot (I had a fan blowing on the ompressor while doing this if i recall correctly)
r404a@80f@180psi will condense, it's been happening on my test rig. I suggest you 'upgrade' to 404a (Better for environment too ^^)
Redwolf
08-06-2004, 03:39 PM
404A is an HFC just like 507.
Best way to find out is to use OEM data chart. You match up X low pressure, X high pressure, with X amp draw.
The other way is to run the compressor with only your gauges on it. So no piping to the condensor, evap, etc. Run it for a few secs and record the pressures.
This isn't the best method and can ruin your compressor if ran to long this way.
um r404 is r507 with some r134a in it..... UPGRADING wont work b/c I think the compressor is shot so I cant use anything. O well have to get another compressor.
runmc
08-06-2004, 04:15 PM
OCN - If the low side and high side doesn't start equalizing upon shutoff, I would suggest you have a restriction in the system somewhere. (it could be moisture)
You will need to do a good triple evac to remove any moisture, possibly replace the filter/drier.
yeah I knonw that... they do equalize..... + if there was a block the low side would read its full potential which obviosly isnt happening :(
LardArse
08-06-2004, 07:24 PM
Cap tube is way too short?
Or it sounds like the discharge line is entering from the bottom and the liquid line coming from the top, giving you problems with condensing the refrigerant.
cap tube is 12ft of .028, the discharge is on the top and liquid is on the bottom.
here is a pic of a system i put together in like 30mins
http://img60.exs.cx/img60/2695/DVC00066.jpg
Ok, I took out the old oil and it was a dark yellow with ALOT of black in it. I could not see the bottom of the pump. I put 2oz of vacuum pump oil in there took it out and then added the rest of the vacuum pump oil.... Now it runs REALY well. I took off the rest of the system and put a schrader ont he discharge and suction nothing else. (redwolf recommended it) and now its pulling a realy good vacuum and the pressure shot upto 250 realy quickly (i opened the high side valve b4 it got too high). Do you guys think it would perform the same with the old oil? If so that would mean the problem is witht he rest of the system.... any ideas????
Originally posted by JSU
now its pulling a realy good vacuum and the pressure shot upto 250 realy quickly (i opened the high side valve b4 it got too
are you using the second compressor to pump the system full of air?
nope, just this compressor by itself
Redwolf
08-08-2004, 10:43 AM
Moonshine
iim not firmiliar with tht expression :(
HawainPanda
08-09-2004, 10:13 AM
did u put the compressor back in ur setup? so still no frost? play with the captube lengh
so its working all ok now?
time to insulate and put it on the mobo
Gary Lloyd
08-11-2004, 03:49 AM
Originally posted by pythagoras
Unless you have a leak the pressure must increase as you add more refrigerant.
Not true. Nice theory, but it doesn't work that way.
Gary Lloyd
08-11-2004, 03:54 AM
Originally posted by JSU
gary its not that, its the fact that no matter how much I put it it wont go over 175psi which isnt enough to condense. The pressure stays at around 150 on the high side and the added refrigeratn only affects the low side. so id have 150/40.
(
You are not listening. It is not about high side pressure. High side pressure has nothing to do with charging the system. The pressure will indicate a few degrees above room temperature and it will stay right there unless/until you grossly overcharge the system, filling the condenser with liquid. If this happens, you have waaaaaaaaaayyyyyyyyy too much refrigerant.
Your problem can be easily solved with a small piece of duck tape. Tape over the face of the guage, so that you can no longer see it. Then charge the system according to low side pressure and frost line.
LardArse
08-11-2004, 04:08 AM
Heh thats true, 175 PSI is your condensing pressure, determined by your condensor temperature.
I thought you had it fixed with your oil change? I see frost in the pic whats the problem?
Gary Lloyd
08-11-2004, 04:20 AM
Originally posted by oc_nightmare
that's happening to me too. dont matter the gas charge i put in the system when i turn the compressor on the discharge line doesnt get hot and the succion remains at the temp it was b4... when i switch the compressor off the system pressure remains in vacuum like if it had nothing in it.
the system was leak tested at 240psi for 12h and no leak was found.... where the hell is the gas goin?:mad:
Your cap tube is plugged. The gas is going to the high side and staying there, because it can't get through the cap tube to the low side. Since the low side isn't getting any refrigerant, it goes into a vacuum and stays there.
oc_nightmare
08-11-2004, 08:16 AM
ty gary:)
going to try fixing it tomorrow;)
Originally posted by Gary Lloyd
You are not listening. It is not about high side pressure. High side pressure has nothing to do with charging the system. The pressure will indicate a few degrees above room temperature and it will stay right there unless/until you grossly overcharge the system, filling the condenser with liquid. If this happens, you have waaaaaaaaaayyyyyyyyy too much refrigerant.
Your problem can be easily solved with a small piece of duck tape. Tape over the face of the guage, so that you can no longer see it. Then charge the system according to low side pressure and frost line.
I tried all differant amounts of refrigerant and nothing happened. Even without looking at my guage it just wouldnt get cold no matter what. Btw I couldnt realy grossly overcharge b/c I was using a little 2pound refrigerant container which has been used a few times b4 so iam ussing there isnt a whole lot left.
The frost is another system. The bigger compressor behind it is the one iam having problems with....
Gary Lloyd
08-12-2004, 02:18 AM
What refrigerant are you using?
What is the low side pressure?
What is the temperature of the suction line a few inches from the compressor?
Iam using r404a with alittle propane. when trying to handle the 12v load with a 1ohm resistor the low side pressure was about 35psi and the whole suction line was frosted unitl about 1 inch form the compressor.
Gary Lloyd
08-12-2004, 11:40 AM
Turn off the heat load.
Remove refrigerant until the frost is at least 6 inches from the compressor.
vBulletin® v3.7.0, Copyright ©2000-2008, Jelsoft Enterprises Ltd.