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paul_h
23-03-2010, 12:27 PM
I've got a ducted system here, very basic, on R22, just a fixed orifice in the condensing unit ('hp' measurements are taken after the orifice on the liquid service valve).

The issue with it is LP is very low, 100kPa, and the compressor cuts out on internal thermal overload as it was running very hot. Nothing in the liquid or suction line is icing up or even cold at all. The only thing that is cool/icy is the accumulator.
First I thought dodgey blocked 4 way valve, so I changed that, no improvement.

Then I noticed it failed to equalise the pressures on the liquid service valve and suction service valve. I thought restriction somewhere on the indoor piping. But after reclaiming that and blowing through with nitrogen it seems alright. After evac of the lines and opening up the liquid valve again, again no pressure at the suction service valve. Really weird that as soon as it's refrigerant/oil in the lines, no flow, with nitrogen good flow, so maybe moisture icing up.
Anyway after a few more cycles of nitrogen, evac running on cool and then reversing flow on heat, this lack of flow through the indoor seems to be OK now, system equalizes quickly so I thought problem fixed.

Retesting the system, LP still 100kPa, indoor unit piping not cool, liquid valve pressure reading 1400kpa.
Condenser not warm, suction line in outdoor unit around accumulator cool, compressor discharge over 100C.

I ran it on heat mode, condenser coil not cold at all, liquid valve pressure reading 1800kPa, suction at compressor is 100kpa again, frost from the orifiice to the condenser distributor like it was very short of refrigerant, compressor cutting out on internal thermal overload.

I retried on cool again, and and for a very short time the liquid valve pressure was 2000kpa (after the orifice) and there was a fair bit of heat coming of the condenser.
But then the condenser cooled down, the pressures dropped, the compressor sound changed back and it was the same as originally pressure and temp wise.

I can't seem to find what is causes this, and think maybe there's something wrong with the scroll compressor discharge, not just or as well as some phantom restriction.
There's no icy spots in the indoor pipes, originally it seems to me a discharge line restriction with is why I changed the 4 way valve, but then I had that dram with no refrigerant flow through the indoor (even though it tested OK with nitrogen), there's nothing in the indoor except the distributor, and none of them were cold. I don't believe there was another orifice because there's no check valves or anything.
Any ideas?

Brian_UK
23-03-2010, 12:36 PM
Make of unit?

Mitsi's have a strainer on the indoor unit flare connectors, sometimes block up although you may see icing there sometimes.

monkey spanners
23-03-2010, 03:22 PM
Had something similar with a r22 toshiba unit, was due to the oil going sh!tty and blocking up the strainers, old oil looked like engine oil when taking gauges off. Scrapped system as rest of it was sh!tty too.

Also had a similar thing with a Fujitsu unit and Daikin unit which i sorted by changing the strainer for a 1/4 sporlan drier just before the capiliary. Could blow through with ofn fine but as soon as you put refrigerant in it would block up.

paul_h
23-03-2010, 03:47 PM
It's another one of those carrier 38DXA136913 units that no one seems to know anything about (I posted a thread asking for diagrams for another one on this job with an electrical problem).

The thing with this unit is as I said, nothing frosty looking like a restriction anywhere, Only bit of frost is around the accumulator. The strainer/orifice/liquid line, distributor, indoor are all warm.

And there's no strainer except in the fixed orifice, and thats clear. Also the weird sometimes blocked/now clear indoor piping, also the compressor gets very hot very fast, cuts out in 5 min, way faster than a compressor running a little short or with a restriction should take to get too hot and cut out.


Could blow through with ofn fine but as soon as you put refrigerant in it would block up. Mmm, seems similar.
I have to add that this system had a bilflow drier in the 'liquid line', I removed that while testing and it didn't help.
I don't think there's anything in the indoor unit like I said as far as strainers or an orifice, just a weld in distributor.

Goober
23-03-2010, 07:29 PM
Me thinks your compressor could be short cycling inside the can....discharging straight into the can?? Would explain the overheating....mmmm but maybe not the low back pressure..would expect that to be higher..could be that it gets to a certain temperture and the crack/problem developes...accumulator frosting while nothing else is is also a bit quirky...logged with oil perhaps???..

Gary
23-03-2010, 08:19 PM
I'm wondering why there is frost at the accumulator? Maybe the accumulator is dodgy or even piped backwards?

mad fridgie
23-03-2010, 08:54 PM
This is an interesting one, liquid pressure seems high if it is after the orifice, I suspect a very rare fault, a broken stem in one off your service valves, indications are the suction.If memory serves me right (and some times is does not!!!) your service pressure ports on the valves will indicate the pressure on the outdoor unit side, is it possible to install a couple of service ports by the indoor unit. If my suspsion is correct you will find that the indoor unit will be at a highish pressure.

Gary
23-03-2010, 09:34 PM
This is an interesting one, liquid pressure seems high if it is after the orifice, I suspect a very rare fault, a broken stem in one off your service valves, indications are the suction.If memory serves me right (and some times is does not!!!) your service pressure ports on the valves will indicate the pressure on the outdoor unit side, is it possible to install a couple of service ports by the indoor unit. If my suspsion is correct you will find that the indoor unit will be at a highish pressure.

That would make sense... but shouldn't the line from the service valve through the 4-way to the accumulator be frosted?

Interesting indeed. :)

Gary
23-03-2010, 09:36 PM
Thinking a piping diagram would be helpful here.

mad fridgie
23-03-2010, 09:46 PM
That would make sense... but shouldn't the line from the service valve through the 4-way to the accumulator be frosted?

Interesting indeed. :)
If it was saturated vapour (liquid hung up in indoor unit) passing through the valve, temp would drop, but when in enters the accumulator (small volume to large volume) further expansion would occur, lowering the temp further, causing the ice. Maybe??

Gary
23-03-2010, 09:53 PM
If it was saturated vapour (liquid hung up in indoor unit) passing through the valve, temp would drop, but when in enters the accumulator (small volume to large volume) further expansion would occur, lowering the temp further, causing the ice. Maybe??

Could be... I'm just taking a wild guess, but generally the problem is wherever the frost is... although your theory fits the pressures better.

al
23-03-2010, 10:07 PM
Paul, just a wild guess but is it possible the expansion device is not working, leading to liquid floodind the evaporator and boiling off in the accumulator?

Also your consistently low suction pressure, is it possible that the suction service valve is damaged (had it on an old split once long time ago,had to braze shraeder in).

From previous poor memory i think the carrier does all its expansion at the outdoor, i don't think there are strainers at the evaporator.........mmm wheat beer....

alec
The issue with it is LP is very low, 100kPa, and the compressor cuts out on internal thermal overload as it was running very hot. Nothing in the liquid or suction line is icing up or even cold at all. The only thing that is cool/icy is the accumulator.
First I thought dodgey blocked 4 way valve, so I changed that, no improvement.

Then I noticed it failed to equalise the pressures on the liquid service valve and suction service valve. I thought restriction somewhere on the indoor piping. But after reclaiming that and blowing through with nitrogen it seems alright. After evac of the lines and opening up the liquid valve again, again no pressure at the suction service valve. Really weird that as soon as it's refrigerant/oil in the lines, no flow, with nitrogen good flow, so maybe moisture icing up.
Anyway after a few more cycles of nitrogen, evac running on cool and then reversing flow on heat, this lack of flow through the indoor seems to be OK now, system equalizes quickly so I thought problem fixed.

Retesting the system, LP still 100kPa, indoor unit piping not cool, liquid valve pressure reading 1400kpa.
Condenser not warm, suction line in outdoor unit around accumulator cool, compressor discharge over 100C.

I ran it on heat mode, condenser coil not cold at all, liquid valve pressure reading 1800kPa, suction at compressor is 100kpa again, frost from the orifiice to the condenser distributor like it was very short of refrigerant, compressor cutting out on internal thermal overload.

I retried on cool again, and and for a very short time the liquid valve pressure was 2000kpa (after the orifice) and there was a fair bit of heat coming of the condenser.
But then the condenser cooled down, the pressures dropped, the compressor sound changed back and it was the same as originally pressure and temp wise.

I can't seem to find what is causes this, and think maybe there's something wrong with the scroll compressor discharge, not just or as well as some phantom restriction.
There's no icy spots in the indoor pipes, originally it seems to me a discharge line restriction with is why I changed the 4 way valve, but then I had that dram with no refrigerant flow through the indoor (even though it tested OK with nitrogen), there's nothing in the indoor except the distributor, and none of them were cold. I don't believe there was another orifice because there's no check valves or anything.
Any ideas?[/QUOTE]

paul_h
24-03-2010, 02:22 AM
I think the frost on the accumulator is just because there's a small amount of refrigerant in there after charging, and as the compressor is sucking OK, that small amount evaporating is leaving frost.
The accumulator isn't heavily frosted up, just a little bit there.
So the concensus here doesn't seem to think that there could possiby be anything wrong with the compressor discharge as it gets so hot pretty quick?
In regards to the service valves, they do seem to work OK, ie I have been closing and opening them to blew through the indoor pipes. And it wouldn't explain the problem equilising or being able to blow through the indoor would it?
Maybe it closes OK but doesn't open, might start with the suction service valve then, cheaper than a compressor.

mad fridgie
24-03-2010, 02:26 AM
I think the frost on the accumulator is just because there's a small amount of refrigerant in there after charging, and as the compressor is sucking OK, that small amount evaporating is leaving frost.
The accumulator isn't heavily frosted up, just a little bit there.

In regards to the service valves, they do seem to work OK, ie I have been closing and opening them to blew through the indoor pipes.

So the concensus here doesn't seem to think that there could possiby be anything wrong with the compressor discharge?
I think I may have explained the wrong way, the seat has come off the valve stem, it will close, but when open it just bobs about (some flow through it)

mad fridgie
24-03-2010, 02:33 AM
The high discharge is a symptom of your low suction pressure, and would be expected, especially with R22

paul_h
24-03-2010, 04:27 AM
Yeah, I follow. Worth trying first I agree.
In regards to high discharge/compressor temp, yes I've come across many systems short of refrigerant or with a restriction that cuts out on compressor overload eventually.
But this system cuts out in a few minutes, which is strange.

Also the other thing, if it was the suction service valve, wouldn't running it on heat mode have normal operation, the the discharge gas would be pushing it open and getting past it OK?
I'll try replacing the valve first, I'm just thinking out loud.

install monkey
25-03-2010, 10:55 PM
was the 4 way valve kept cold when brazing?try unplugging the coil when energised to prove changeover. could be discharge gas going straight back into the suction line.

nike123
26-03-2010, 11:01 AM
Paul, did you checked air flow in indoor unit?

Temprite
26-03-2010, 11:07 AM
G'day Paul.

Have you reclaimed the whole charge and checked with the weight specified on the system?

Sound like moisture to me blocking up expansion device and/or strainers.

When you have the system off for a period moisture thaws out and proper flow returns to the low side, then when you turn the system on again flow is there for a short time until it blocks again and accumulator frosts because gas is boiling off inside it.

Running like this will overload the compressor quickly.

I would reclaim and weigh the charge and compare it with weight on label, pressure test for a couple of days and if it drops find and repair leak. Check at the bottom of the evap near drain pan or anywhere moisture could be taken in. Then remove the strainers and replace with new ones or bi flo dryers. Make sure you give it a really good vac preferably with a micron guage attached.

Has any one added gas to the system lately because of a gas leak?

Had a system about 6 months ago doing the same thing, it had a leak on the indoor header and had taken moisture in there.

Good luck.

paul_h
29-03-2010, 03:08 AM
No, it's charged right and not a leak.
History of the unit is it stopped working a while ago, someone came and said Short of refrig and added 1kg R22.
Still wasn't working so I was called. I reclaimed and found the unit 1kg overcharged. So no leaks in the system or chances of moisture especially now as I have vacced out a few times
I've reclaimed evacuated and recharged by weight, and re-evacuated a couple of times after blowing nitrogen through.

Airflow is good, and the suction would be cold and low pressure anyway, not warm and low pressure.

Gary
29-03-2010, 07:14 AM
Hmmm... an interesting problem.

On fixed orifice reverse cycle machines, the fixed orifices have a built in check valve which allows full flow in one mode and orifice flow in the other mode.


I'm wondering what would happen if the outdoor check stuck in the closed position, allowing flow only through the orifice.

The liquid flow would then be through both orifices in series, making for some very strange pressures.

The problem with this theory is that the system should function normally in the heat mode. Its hard to imagine that both check valves could be stuck at the same time... but I suppose that's possible.

Hmmm...

Temprite
29-03-2010, 11:09 AM
I retried on cool again, and and for a very short time the liquid valve pressure was 2000kpa (after the orifice) and there was a fair bit of heat coming of the condenser.
But then the condenser cooled down, the pressures dropped, the compressor sound changed back and it was the same as originally pressure and temp wise.

The fact that the system runs ok when you start up after evacuatting the lines then fails after some time, still sounds like moisture to me.

I dont know the full history of this unit but is it possible that system has ingested moisture and oil now has a high water content. I have evacuatted systems before that have taken in large amounts of moisture and recharged only to find that they get a blockage again. Once I removed the compressor and drained the oil and tried again they would start operating correctly.

If you evacuatte with a micron guage you will be able to tell if you have moisture or not.

Cheers

paul_h
29-03-2010, 03:58 PM
Yeah I agree, it could be the indoor blocking up due to moisture. It was my second guess after what I have seen and reported.
Problem: The orifice is in the outdoor and it's a large fixed orifice, and there's 1500kPa pressure in the line after the orifice, also nothing in the indoor or 'liquid' line is cool like there's a restriction, same for the evap. I even cut out the drier thinking that may be it.
The other thing is when I was just purging through the indoor circuit using the schrader access ports on the service valves (with the valves wound in closed), I got a blockage, even though the lines were evaced and cleared with nitrogen, and it was a nice warm day and I'd been there for hours. Makes moisture less likely, but something physical/solid blocking the indoor circuit. As the unit had no frosting while running at the indoor, and there's no mysterious kinks, or strainers/orifices, valves etc, I guess the SSV is the only thing I can suspect based on some other members past experience. If it isn't that, then its heaps of moisture in the system and probably not economical to repair right?

It's definitely a hard call to make, I was 100% convinced about moisture when I was there and exhausted that possibility to my mind after spending so much time there, which is why I came on here to seek opinions on whether it could be something else. There's no physical restriction on the indoor when not using the suction valve (ie disconnecting the flare), but there definitely is a restriction when connected.
But there's no orifice or anything in the indoor, so no reason why it would be blocked up with moisture, considering the system had a drier (which is rare for a split, and even they don't block up 99.99% as the temps are usually above 0C).
I'm going to try the SSV and let you know how it goes.

brunstar
29-03-2010, 10:40 PM
paul, it sounds like a blocked expansion valve on the indoor unit.
If it is an old one you will find it may have an externally equalised expansion valve.
The bulb on this may be faulty which is not allowing the refrigerant to be metered into the indoor unit.
If you measure across this then you should see the temp drop there.
The other thing it could be is a capillary blocked on the outdoor unit at the end of the condenser coil..

al
29-03-2010, 11:19 PM
Is there a distributor fiited internally? Could some of the tubes be blocked?

Alec

oldesky
30-03-2010, 12:26 AM
Paul
Some of those orifice assemblies have an orifice that moves back and forth inside the tube depending on the refrigerant flow. You may have one that is sticking. I would suggest you removed it and install a biflow TX valve with a pressure limiting power element. Parker make a biflow TXV that I have used in the past to replace thermo electric valves in A/C units and I found them to work well.

tradybrad
30-03-2010, 10:56 AM
has system got bi flow liquid line filter drier in condenser most carriers do maybe partially blocked have had this issue with carriers same model

Levi
30-03-2010, 11:13 AM
Have you checked the current load on the compressor starting and running. Seems to me that you have an old compressor and it has finally given it up.

paul_h
30-03-2010, 07:19 PM
Hmmm... an interesting problem.

On fixed orifice reverse cycle machines, the fixed orifices have a built in check valve which allows full flow in one mode and orifice flow in the other mode.


I'm wondering what would happen if the outdoor check stuck in the closed position, allowing flow only through the orifice.

The liquid flow would then be through both orifices in series, making for some very strange pressures.

The problem with this theory is that the system should function normally in the heat mode. Its hard to imagine that both check valves could be stuck at the same time... but I suppose that's possible.

Hmmm...
This system only has the one orifice in the outdoor.
As it's a simple bidirectional orifice , no check valves and nothing in the indoor needed or used unlike a TXV system that only works in one direction.
Unfortunately no diagrams or anything available ( I asked before for another unit because I had no luck). One company controls carrier/toshiba/brivis down here, and they make a lot of money by denying anyone information, and selling parts at huge mark up, and I couldn't find anything matching on overseas model numbers/types.


Is there a distributor fiited internally? Could some of the tubes be blocked?

AlecThere is a dizzy, none of them were cold or frosty at all.


has system got bi flow liquid line filter drier in condenser most carriers do maybe partially blocked have had this issue with carriers same model The drier was external, ansd I removed that, still the same. Don't forget, that I had 1500kPa pressure leaving the outdoor unit, it just wasn't coming back.

Have you checked the current load on the compressor starting and running. Seems to me that you have an old compressor and it has finally given it up.I had low suction pressure though. Maybe something might be wrong with it, but there seems to be something else wrong too.
I've written off many compressors with high suction pressures and cutting out on over load, and maybe there is something wrong with the compressor. But I'd like to see high suction pressure and overload before I write off the compressor. I've replaced a few burnt out compressors, only for the new compressor to have high temps and low pressures because there is a restriction or something that caused the original compressor burn out. Bad enough to quote, do the replacement then say there's more problems after a burn out. at least this time the compressor is still running so I can diagnose the restriction/cause of very soon compressor failure part before I replace the compressor if need be.
One of the worst parts about a job for me is if you do a comp replacement, or a leak repair (proven a leak because you weighed what you reclaimed), and after recharging, the system is still stuffed due to a restriction somewhere. I real sinking feeling and the worst thing ever IMHO. Lots of wasted time and refrigerant, and you've got to explain yourself how it's not your fault :(

al
30-03-2010, 09:52 PM
Paul

You're down to process of elimination, being self employed myself you've got to justify your time and genarally that's by charging the customer, difficult to do unless they trust you to sort it.

Cutting the orifice out and shoving nitro down the suction will prove suction line and distributor are clear, gives a chance to physically check the orifice too, although i'm not familiar with them, more a txv man meself...

sedgy
30-03-2010, 10:12 PM
faulty compressor releaf valve?

Gary
31-03-2010, 06:11 AM
This system only has the one orifice in the outdoor.
As it's a simple bidirectional orifice , no check valves and nothing in the indoor needed or used unlike a TXV system that only works in one direction.


Hmmm... failure to equalize would indicate a liquid line restriction.

The liquid access port being after the orifice in cooling mode, I would expect the gauge to read lowside pressure. That pressure being unusually low with proper charge would indicate liquid line restriction.

In heating mode, with the gauge port before the orifice, the gauge access should read high side pressure. If there were a restriction after this point, the suction line gauge would read unusually low and the liquid gauge would read near indoor ambient. Again, indicating a liquid line restriction.

The only devices in the liquid line are the drier, the orifice and the liquid shutoff valve. The drier was removed with no improvement... so that leaves the shutoff valve and the orifice.

Still... I would expect frost at the point of restriction.

Temprite
31-03-2010, 10:59 AM
Retesting the system, LP still 100kPa, indoor unit piping not cool, liquid valve pressure reading 1400kpa.
Condenser not warm, suction line in outdoor unit around accumulator cool, compressor discharge over 100C.

I agree with Gary. If there is only one orifice and it is in the outdoor unit and you are on cooling I cant see how you are getting a liquid line pressure reading that high as it is after the orifice and should be lower. Unless there is another device in the indoor.

philjd26
04-04-2010, 12:35 AM
paul,
that suction accumulator sounds as if it has something in there. i would braze srader valves on the inlet and out let just to confirm nothing is causing a resistriction.

rgrds phil

lawrence1
04-04-2010, 01:27 AM
I think Temprite is correct and that there is an indoor orifice blocked.
LJ

gman082
05-04-2010, 12:42 AM
Unless there is another device in the indoor.
Now we're on the right track....:D

paul_h
11-04-2010, 02:39 PM
There's definitely a restriction on the indoor, whether it's a problem or whether it's by design I don't know. The outdoor unit has no check valve or piping bypassing the outdoor flare orifice, and there's no flare orifice that I can see on the indoor (I have seen systems with two orifices, check valves etc before and other systems etc). The indoor on this unit just has a distributor with 4 x 1/8" capillaries off it)
Nitrogen flows freely through the indoor circuit, but when you use refrigerant it keeps a lower pressure, like it's just expanded and cooled.

edit: BTW as soon as power is applied to the unit, the RV solenoid kicks in and the pressures equalise. I don't know if this means anything, it could be because it's wired like many USA units, activate 4 way valve to cool, unlike the standard activate 4 way valve to heat here and europe. But I'm not 100% sure what it could mean as far as compressor valve or 4 way valve blockage; and pipework restriction for it to so quickly equalise on 4 way valve operation, but fail to equalise between the liquid valve and suction valve with the system switched off.

The compressor is cactus IMHO, I found out the HP switch is on a schraeder, so I put a HP gauge on there, and it's the same pressure as the liquid line after the orifice, 1200kPa for both on my last visit, as it was cooler than the previous time I was there and the liquid line was 1500kPa. Also it sounds pretty sick to my ears, and like I said, it gets really hot really quick. I know it's normal for the liquid line pressure from an outdoor tx/orifice system to be higher than SP, most ducted small units I have worked on have had between 700-1000kPa on the liquid line from the outdoor after the TXV depending on HP, SP and ambient, when the suction pressure was 350-500kPa. But the liqid line was never close to the discharge pressure.
BTW
Nothing was wrong with the suction service valve.
So... :eek:

edit: Also there is a schraeder between the accumulator and compressor, and it reads the same suction pressure as the suction service valve before the accumulator.

late edit: Also a little bit of oil came out when blowing through the evap, it wasn't really thick/dark etc like Monkey spanners experienced.
Extensive reno have been carried out since this a/c was installed owners suggest a massive job would be required to replace the a/c (steep shingled two story house in one of the cities old 1940s areas

Gary
11-04-2010, 03:22 PM
On reverse cycle machines, the orifice and check valve are often combined into one device.

Gary
11-04-2010, 03:30 PM
edit: BTW as soon as power is applied to the unit, the RV solenoid kicks in and the pressures equalise. I don't know if this means anything, it could be because it's wired like many USA units, activate 4 way valve to cool, unlike the standard activate 4 way valve to heat here and europe.

The assumption is that if the RV coil fails it is better to overheat your house than to freeze/burst your water pipes. Of course, this assumes you have indoor plumbing. :D

Gary
11-04-2010, 03:42 PM
There's definitely a restriction on the indoor, whether it's a problem or whether it's by design I don't know. The outdoor unit has no check valve or piping bypassing the outdoor flare orifice, and there's no flare orifice that I can see on the indoor (I have seen systems with two orifices, check valves etc before and other systems etc). The indoor on this unit just has a distributor with 4 x 1/8" capillaries off it)


Keep looking... there is an indoor orifice/check valve somewhere in that liquid line. It was probably hidden during the reno.

paul_h
11-04-2010, 05:10 PM
How does a check valve work without bypass piping around it?
If you have a metering device restriction(cap, TXV orifice), and a parallel check valve around it, then direction flow determines whether the flow goes though the restriction, or bypasses it via a check valve.
No parallel piping around the restriction (orifice, capillary, TXV), then check valves (even if inbuilt to an orifice) are impossible?
There's no parallel piping for a check valve to be fitted to, therefore only one path, always through the outdoor orifice?

edit: obviously to me this system has more than one problem, so I'm open to new ideas.
But how can a system which never has parallel piping across a ref flow control device, ever have check valves and more than the one ref flow control device if it's a simple bi-flow orifice?

Condenser goes straight out through the orifice, no bypass pipeline around the orifice. To me that means no check valve, as it has to be parallel around the outdoor orifice doesn't it?

Gary
11-04-2010, 05:23 PM
How does a check valve work without bypass piping around it?
If you have a metering device restriction(cap, TXV orifice), and a parallel check valve around it, then direction flow determines whether the flow goes though the restriction, or bypasses it via a check valve.
No parallel piping around the restriction (orifice, capillary, TXV), then check valves (even if inbuilt to an orifice) are impossible?
There's no parallel piping for a check valve to be fitted to, therefore only one path, always through the outdoor orifice?

edit: obviously to me this system has more than one problem, so I'm open to new ideas.
But how can a system which never has parallel piping across a ref flow control device, ever have check valves and more than the one ref flow control device if it's a simple bi-flow orifice?

Condenser goes straight out through the orifice, no bypass pipeline around the orifice. To me that means no check valve, as it has to be parallel around the outdoor orifice doesn't it?

The orifice plate/piston is spring loaded. In one direction the liquid flows through the orifice. In the other direction the orifice is pushed out of the way to allow full flow.

daneel
13-04-2010, 01:36 AM
There's definitely a restriction on the indoor, whether it's a problem or whether it's by design I don't know. The outdoor unit has no check valve or piping bypassing the outdoor flare orifice, and there's no flare orifice that I can see on the indoor (I have seen systems with two orifices, check valves etc before and other systems etc). The indoor on this unit just has a distributor with 4 x 1/8" capillaries off it)
Nitrogen flows freely through the indoor circuit, but when you use refrigerant it keeps a lower pressure, like it's just expanded and cooled.

Hello, you have what is known as a piston accurator for the indoor expansion device. It is a small bullet shape with an orifice. there are no check valves involved per se. In the AC mode, the bullet shaped nose fits in a pocket and refrigerant is metered through it. In the heating mode, the refrigerant moves the bullet back to a stop and the liquid moves around it back to the outdoor unit. Most indoor coils come with 1 or 2 of these bullets depending on which condensing unit you're going to use. It's in the indoor unit prior to the distributer. There should be flare nut or other mechanical fitting so the correct orifice can be installed in the field.

When you flow nitrogen through it is the reversing valve also energized? If not, you're bypassing the indoor expansion device and you will get a good flow. Also check the distributer tubes by temperature to make sure one of them isn't feeding properly.




edit: BTW as soon as power is applied to the unit, the RV solenoid kicks in and the pressures equalise. I don't know if this means anything, it could be because it's wired like many USA units, activate 4 way valve to cool, unlike the standard activate 4 way valve to heat here and europe. But I'm not 100% sure what it could mean as far as compressor valve or 4 way valve blockage; and pipework restriction for it to so quickly equalise on 4 way valve operation, but fail to equalise between the liquid valve and suction valve with the system switched off.


Most USA units energize the rev valve for cooling mode. When de-energized, pressures quickly equalize. If still energized after thermostat is satisfied, pressures will not quickly equalize.




The compressor is cactus IMHO, I found out the HP switch is on a schraeder, so I put a HP gauge on there, and it's the same pressure as the liquid line after the orifice, 1200kPa for both on my last visit, as it was cooler than the previous time I was there and the liquid line was 1500kPa. Also it sounds pretty sick to my ears, and like I said, it gets really hot really quick. I know it's normal for the liquid line pressure from an outdoor tx/orifice system to be higher than SP, most ducted small units I have worked on have had between 700-1000kPa on the liquid line from the outdoor after the TXV depending on HP, SP and ambient, when the suction pressure was 350-500kPa. But the liqid line was never close to the discharge pressure.


Pressure drop through coils varies. With such a low suction pressure as you're having it prolly would'nt take too much time to overheat it, specially if its a scroll with no suction liquid injection.

philjd26
13-04-2010, 05:13 PM
im thinking the pour point of something in that pipe work is dropping the pressure( hydrolic oil), at this stage moisture content has got to be eliminated as the compressor windings would have been knackered due to the reaction moisture/refrigerant,if there was that amount!!!

unless some little roasty has being geeing around with the inserts/phails of the tev's...wrong size/refrigerant type....

i dont know, let me know what the out come of this one is..

rgrds phil