Symptoms of a restriction

[Jova007200]

Before I go on, a little bit about what I've done here...

I've a water chiller system that I designed and built. Now, before you laugh, I didn't just throw the thing together. I used reasonable judgement, advice from engineers that I've worked with over the years, and as much research as I possibly could to do it as correctly as possible.

I did it legally with the appropriate certifications and reasonable knowledge. But I am by no means a experienced technician. So I'm asking for your help. I'll understand if you decline.

Ok....

I charged the system until I was satisfied with the level of superheat and subcooling stability. It is a TXV based system using R507.

Before I ran into a problem, I had the following characteristics.

Subcooling = Avg ~12F
Superheat = Avg ~10F
Condensing Temp of 100F
Discharge Temp of ~115F including heat of compression.
Suction Pressure - 15PSI to 30PSI (Stable, changing as the coolant temp around the evap dropped). 15 PSI seemed to be the ultimate minimum, as the coolant temp would reach the desired 0F at about that point.

The TXV during normal operation exhibited limited or no hunting, and pressure would remain stable.

At some point, something changed. I should mention that the system was thoroughly leak checked with dry nitrogen. It held vacuum, and I even checked it with my Halogen sniffer after charging. It was leak free, and air/moisture free (at least everything pointed in that direction).

Upon running what I thought would be the final test, I set the thermostat, and activated the unit. The unit never stabilized.

New Specs observed

Subcooling : 50F
Superheat : 20 - 35F (rapidly oscillating)
Discharge Temp : 170F and climbing
Liquid Line Temp : 70F (100 !!! Delta T)
Discharge Pressure : 320 PSI
Suction Pressure : 5-8 PSI with random hunting in that range

So, after cursing in multiple languages, it seemed obvious that I have a restriction that didn't exist before. But where?

I deactivated the temperature controls, and pumped the refrigerant to the high side. I inspected the TXV screen, it was clear. No debris.

I removed the bulb from the suction line. I activated the system again. I squeezed lightly with my palm, the valve opened. I put it in a cup of ice, it closed up.

The liquid line was a mild 70F. The discharge temp would continue to rise given the ridiculous pressure differential and the fact that nothing was getting into the condenser without a serious fight. Needless to say, I didn't want to murder the compressor (Tecumseh HG Rotary), so I shut it down after a short trouble shooting phase.

Given that the system operated properly before, I can't settle on a problem.

The High Superheat and Subcooling tell me that something is holding refrigerant in the condenser. Suction pressure is low, so immediately I think of the TXV. Though, the valve responded to test promptly. It should probably be a PZ charge, but even so it worked prior.

If the drier is mildly restricted, should I not read a temperature change across the thing? It registers none. I threw a gauge on the receiver and detected no pressure difference either. So if its restricted, it isn't severe. I checked for a temperature delta across the solenoid to see if IT had a restriction that was metering refrigerant, and detected nothing.

I'd like to think it is a defective element.... But it failed at least the palm and ice test. I wouldn't expect a plugged filter to cause a low suction pressure if it didn't cause a notable pressure drop on the other side.

What do you think? :\

[mikeref]

I would remove the TX bulb from suction line and observe the suction pressure. You didn't mention that when you removed it before. 14.7 PSI is 100 KPA so your lower pressure reading of 15 PSI when your kit was working...is rather chilly at -32*C / -25 ish *F.
No mention of Vacuum quality and now sub-cooling is 50*F/ 28*C? I'm leaning towards contamination by moisture.

[nike123]

Did you used nitrogen as protective atmosphere during system assembly (brazing)?
If not, you certainly need to change filter dryer!

If that doesn't help, than you should recover refrigerant, make vacuum again until 500 (or lower) microns, and isolate vacuum pump and check to see if vacuum level is changing up more than 100 microns per hour at first, and 1000 microns per 24 hours. If you have greater rate than 100 microns/h, vacuum further. If at the end you does not have rise more than 1000 microns per 24 hours you are done with vacuum check and you can proceed with charging fresh (verified) refrigerant.

When you say "it held vacuum" what was vacuum level expressed in microns of mercury (or Torrs or Pascals).

What is the model# of TXV? Oriffice size?
What is compressor model#?

Did hunting of TXV happened after system reached its design temperature and not during pull-down!
Is the air flow at evaporator correct and checked with air flow meter?
Do you have suction accumulator?
How long was compressor oil exposed to atmosphere air (cumulative)?
Same question for filter-drier!
What is filter-dryer model#?
What oil you are using?
Did compressor used previously mineral oil and now POE?

[mikeref]

You say it is a Tecumseh HG compressor? Not a Tecumseh HGB-1000 belt drive by any chance.
More info needed as Nike ^ asked for. Send us some pictures. :)

[Jova007200]

I'm sorry, I initially gave the micron value but I edited my post and it got deleted. I evacuated to just under 300 microns. I gave it an hour and it rose only 45 Microns. Based on my experience in manufacturing, I did not consider that a bad rise.

I wasn't one of those guys that thought purging was just "the man" trying to control me during my tenure with Carrier. So, I purged while brazing. (I really did hear several guys complain that the engineers like to tell them what to do because they thought purging was unnecessary).

I took the bulb off after the trouble persisted to check to see if the valve was sticking closed due to a blown element charge. It responded to my hand and to ice. Even though the charge is a "C" charge, the system worked perfectly fine before this happened.

Now, your other questions...

"What is the model# of TXV? Oriffice size?"

Sporlan SBFSE-A-C - The Orifice is an "A" orifice. I should mention that I intend on changing the Element to a Z charge.

"What is compressor model#?"

HGA9468ZXA using PVE Oil.

Did hunting of TXV happened after system reached its design temperature and not during pull-down!

TXV Hunting happened after the restriction showed itself. It happened throughout the entire operation. It did not hunt during stable operation prior to the problem.


"Is the air flow at evaporator correct and checked with air flow meter?"

The evaporator is submerged in a Propylene Glycol solution. Its a chiller. GPM is near 4 - 5 at the lower temperatures.

"Do you have suction accumulator?"

Yes, the accumulator is attached to the compressor.

"How long was compressor oil exposed to atmosphere air (cumulative)?"

That's hard to say. I didn't expose it to air until I was ready to braze the connections, and I immediately purged with nitrogen as soon as I was able. If I had to stop assembly at any point, the compressor was isolated. What I don't know is if it was exposed to air prior to my acquisition, as it was a surplus unit.

"Same question for filter-drier!"

The filter drier was exposed to atmosphere for as long as it took to remove the packaging and install it into the line. It may have been exposed to limited atmosphere during the time it took to install the sight glass, Receiver, and solenoid valve before the TXV.

The Solenoid valve is an R30E124. Parker 3/8" port.

"What is filter-dryer model#?"

Sporlan C083-S. It is going to be replaced, and my question to you is, would it be out of the question up size to a C163 on there?

"What oil you are using?"

The compressor came with a PVE oil charge. No previous charge of any other kind.

_______________

Additional Info :

The system uses an oil separator. Initially, I had its oil drain controlled by a solenoid valve on a delay cycle that only ran once per running cycle. I decided that I botched that badly and changed to a on/off repeat delay. It also pumps down at the end of each cycle for an unloaded start via the thermostat controlled solenoid on the liquid line. Compressor is controlled by low pressure switch.

I don't think I'm leaving anything out.

[The Viking]

If there is a restriction there will be a temperature drop.

Follow the refrigerant young man, follow the refrigerant...

Start at the condenser outlet and follow the liquid line to the evaporator and then on to where your suction line gauge is connected, where does it get cold? There lies your restriction.

:cool:

[Jova007200]

If there is a restriction there will be a temperature drop.

Follow the refrigerant young man, follow the refrigerant...

Start at the condenser outlet and follow the liquid line to the evaporator and then on to where your suction line gauge is connected, where does it get cold? There lies your restriction.

:cool:

That is precisely why I am perplexed... :( I can't find a temperature change. That seems to suggest that the drier is indeed restricted. Though, would that cause the suction pressure to drop so severely? I did not read a pressure drop through the drier. Pressure was equal on either side. I even calibrated the gauge before I took the reading just to be 100% sure.

[install monkey]

oil loggin in the evap?- if liq line appears ok with no temp drop- you did say it dropped to 15psi and it pumps down when at setpoint

[Jova007200]

oil loggin in the evap?- if liq line appears ok with no temp drop- you did say it dropped to 15psi and it pumps down when at setpoint

I actually considered that my system might have become oil logged given the way I initially had the separator drain set up. Though, I figured it would have affected the drier, or pooled in the receiver. I didn't think of the evaporator in that fashion. However, shouldn't that create less superheat rather than more?

The thing is, the evaporator behaved as normal. (At least as it can be inferred). The system pulled from 60F to -5F with relatively rapid succession. Twice as quickly if not more with the lower temp. So I've ignored the evaporator as a potential issue, mainly given the superheat.

[install monkey]

just re read the 1st post- you say water chiller- water in evap- maybe frost caused internal plates to reduce flow rate on your fridge side

[install monkey]

any anti freeeze in your water circuit, flow switch to stop fridge if pumpp fails, water strainer on the return? frost stat on water outlet?

[Jova007200]

The solution is 50/50 Propylene Glycol/Water. Hang on, though. It isn't a Plate HX.

I designed and built the evaporator using a coil in shell design.

I haven't installed a flow switch since I'm conducting controlled tests at this point. During one of these tests, the system began to behave strangely. The coolant pump is functioning normally.

[install monkey]

when you run it - de energise the solonoid on the oil sep oil return line, see if theres any change

[nike123]

The TXV during normal operation exhibited limited or no hunting,

It looks like it was at beginning of that possibility.


When you will be changing filter dryer, I would change orifice to one size smaller. Leave TXV superheat adjustment screw to factory position.

[Jova007200]

when you run it - de energise the solonoid on the oil sep oil return line, see if theres any change

The solenoid is only energized for a limited period of time, then it deactivates. The idea is to drain any oil that is inside and then close for a specific time period.

[Jova007200]

It looks like it was at beginning of that possibility.


When you will be changing filter dryer, I would change orifice to one size smaller. Leave TXV superheat adjustment screw to factory position.

The HVAC Tech I asked at work said the same thing. Though, couldn't an incorrect charge selection cause the same? Any Hunting that showed at all was originally VERY limited to the first minutes of start up.

Changing the element will require a new valve, which I'd rather avoid if possible. I am taking it that you are convinced that the F/D is the cause of the problem.

[nike123]

No, I am not, but I would like to follow symptoms. Hunting means inability of valve to adjust its capacity to capacity of system because of oversized valve or bad bulb position, or wrong element charge or all together.

If filter drier is slightly clogged as oppose to clean filter at beginning, than, i suppose, those symptoms are going to be more visible now than before.

Since you opening system, it is better to address all possible causes.

Since I am not familiar with Sporlan valves, can you present here your TXV selection data?

[Magoo]

At a guess and under sized liquid line during pull down /high load condition. High discharge temp, TXV starving and hunting. High liquid line temps.
Could be totally wrong though.

[RANGER1]

Could the system have pumped down most refrigerant into condenser & assume liquid receiver & receiver is to small or system overcharged?
Maybe try to transfer some of the refrigerant out of the system or to evaporator & suction trap or slop pot before starting again.

[nike123]

Many times after system assembly here, where our technicians not using nitrogen much often in brazing process, I was having problems with superheat and TXV functioning properly. Many times pressure drop/temperature change at filter is not observed by our tools. It doesn't mean that they are not there, they are simple not visible at our inaccurate measuring equipment.
After filter change, everything comes to normal.

I translate that as system is at near the edge before, and edge is crossed later!
After filter change, system is again near the edge, and we can expect more problems in future, but for now, it functioning properly.

Sometimes good for pocket and sometimes bad for reputation.;);)

Triple check your TXV selection and correct everything which is wrong. It will cost you less in future. And, since this is your system, it is in your best interest to change valve to correct bulb charge and correct size of orifice/capacity.
If it is oversized, and you have small restriction, Magoo-s scenario is very likely!

Another question! Why you selected R507 and not R404A as refrigerant, since TXV is made for R404A?
As I read Sporlan literature, there is another TXV for R507, the BFPE one!

Picture of evaporator and details of bulb location and equalizer line would be of help here.
Check equalizer line for temperature change.

I calculated little and appears that more problems with that system design are disclosing.
That Sporlan valve is for capacities in range 1/2 to 1 TR. (1,8-3,5 kW)
That compressor has displacement of 16 cc which translates to about 1kW cooling capacity at evaporation of 15psi (-31°C) and condensation of 100°F (37°C) for R507.
Therefore, at these working temperatures TXV is over-dimensioned and not in control.
Also operating range of that compressor is as Tecumseh is stating "Commercial Back Pressure". I believe that operating range at -31°C is defined as Low Back Pressure and out of that compressor working range.
I cannot find anywhere in specifications for that compressor evaporating temperatures lower than 0°F.

[Jova007200]

The TXV Charge Selection was a misnomer, but considering that initially the machine worked as expected, I didn't immediately consider it a problem. Since then, I'll admit that that was an error on my part and I'm going to change at least the element. I came here because I wasn't sure if that would be enough, but I didn't want to replace the whole valve if unnecessary.

The bulb is at the evaporator outlet at 2 o'clock on a horizontal span of tubing.

I understand that my system isn't designed perfectly, and I know I made some errors. However, should it not have misbehaved completely from the start?

That said ; this is what I'm going to do:

1. Change txv size & element (1 orifice size down and charge for 507)
2. Replace filter drier and sight glass. (Is upsizing the F/D a problem?)

As for the compressor, I bought what I could get my hands on that fit the application as closely as possible. I can always alter the application of that, but it seems that the TXV problem is a must change.

[nike123]

The bulb is at the evaporator outlet at 2 o'clock on a horizontal span of tubing.

Is bulb placed before equalization line connection at least 10 cm from joint?


I understand that my system isn't designed perfectly, and I know I made some errors. However, should it not have misbehaved completely from the start?

As I said earlier, maybe slight filter drier restriction has been sufficient that system goes over the edge of visibility!


That said ; this is what I'm going to do:

1. Change txv size & element (1 orifice size down and charge for 507).


I would use charge with MOP!


2. Replace filter drier and sight glass. (Is upsizing the F/D a problem?

Nope, but make it easily demountable (flaring connections)! Later, when everything is sorted, you can change it to solder type.


As for the compressor, I bought what I could get my hands on that fit the application as closely as possible. I can always alter the application of that, but it seems that the TXV problem is a must change.

I don't see how can you alter the application, if you need 0°F glycol solution temperature. Than -20°F of evaporation is must!

You can only alter compressor to proper type for that purpose, or change purpose of system.

That compressor will overheat at that low evaporation temperature, since its motor is too powerful for that application range, and only cooling that compressor gets is from suction gases which are, at that evaporation temperature, not dense enough (small mass flow).

You will probably need liquid injection if you try to keep that compressor at that evaporation temperatures.

[Jova007200]

I don't see how can you alter the application, if you need 0°F glycol solution temperature. Than -20°F of evaporation is must!

You can only alter compressor to proper type for that purpose, or change purpose of system.

That compressor will overheat at that low evaporation temperature, since its motor is too powerful for that application range, and only cooling that compressor gets is from suction gases which are, at that evaporation temperature, not dense enough (small mass flow).

You will probably need liquid injection if you try to keep that compressor at that evaporation temperatures.

The application desired a 0F temperature, if I change that to desire a higher temperature, I don't see how that is any different than "purpose." We're talking about the same thing there.

The compressor shell temperature during normal operation was not high. I kept an eye on it for that same reason that you are describing. I bought the compressor and then eventually realized that I had a problem. I didn't record it, so my memory wouldn't be reliable.

I am considering the compressor change as you have suggested.

Still, if the system was "on the edge" as you describe, how could it have possibly controlled the system with acceptable Superheat, Subcooling, and Discharge temepratures? (et al)

It would seem to me that there should have been SOME type of symptom of a problem. The TXV wasn't hunting after what I would expect for an immediate start up before the sight glass clears and the receiver fills up sufficiently.

That's kind of why I'm still partly scratching my head. I measured all of the same parameters before the problem arose. System run time was 12 hours and we're talking about a hunting time of less than 1% of that (at least that which was recordable). Is it really that much of a night and day scenario?

___________

That said, if I want to maintain low temp, what are some of the things I can do assuming I don't change the compressor.

You mentioned liquid injection, are there other things I can do? How about limiting superheat to a slightly lower level the promote a bit more mass flow?

I'm open to suggestion.

[Jova007200]

Update : Today, I went out to check the system. Last time I worked with it I recovered the refrigerant. Then I vacuumed (not full vac).

It has been in this state for an entire week. I checked the gauge, and it was at 1800 Microns and stable, so I don't need any more insults to my brazing technique... :p

HAH! hehehe.... I'm sorry, I just get really insulted when people suggest I might have had a leak. This is something I did for years and leaking is something that my joints did NOT do. No one could call my joints ugly either inside or out. I always purge. :)

[Gary]

Sounds like non-condensables (air/nitrogen) to me.

Possibly there is a section of the system that is not being evacuated. During operation, a valve opens allowing air to flow from that isolated section into the rest of the system.

The alternative would be a gross overcharge... which can in fact cause hunting, but would tend towards low superheat not high.

[Jova007200]

Sounds like non-condensables (air/nitrogen) to me.

Possibly there is a section of the system that is not being evacuated. During operation, a valve opens allowing air to flow from that isolated section into the rest of the system.

The alternative would be a gross overcharge... which can in fact cause hunting, but would tend towards low superheat not high.

I ruled out the latter because of high superheat. I didn't add any charge when the problem began given that subcooling climbed as it did.

Though, as far as air in the system, I'm not sure where it could be getting in if that is indeed the problem.

I evacuate from the low side and the high side. There is one space that is isolated by a solenoid valve and two check valves on either side of the compressor. I open that solenoid when I evacuate the unit. I also take the vacuum reading from a port on the discharge line that has access to the compressor's discharge port. That is the same run of tubing that is isolated by check valves and the solenoid valve. When the solenoid opens, it has access to the suction line via the oil separator drain port.

The discharge line access near the condenser is after the check valve. I would expect that to prevent that from sealing.

So, if it is indeed air, and there are no leaks. Where does the air come from?

- Discharge line Port - Access to condenser, liquid line, receiver to solenoid valve
- Suction Line Port - Access to solenoid valve, txv, evaporator, suction line, discharge line, and compressor

The latter two via the sep drain solenoid valve.

[Gary]

When you recovered the refrigerant, did the pressure and temperature correspond?

[Jova007200]

When you recovered the refrigerant, did the pressure and temperature correspond?

I didn't take note. I'd have to go back and check the cylinder. I'm not in the same place as it is right now, and it will be some time before I can check.

Lets assume air got into the system. And also, it is known that there are no leaks.

Where would the air come from?


All components are accessed during vacuum.
Compressor is accessed via Discharge Line
Check valve in suction line for pump down
Check valve down stream from oil separator
Vacuum port accessed on both sides of the discharge check valve by means of the open solenoid valve at separator drain
Second solenoid valve can be opened for full system access by both vacuum ports


So the compressor is the only spot that doesn't have direct access to both sides for evacuation. Would the accumulator be isolated from the vacuum?

As I understand these types of rotary compressors, the vanes only seal effectively during operation, and will allow system equalization once the compressor shuts off (hence the need for a check valve for a pump down cycle.

I'm listing as much detail as I can think of, because I'm not convinced that air is in the system. But I do agree that the symptoms do seem to be there.

The question is, should it not have behaved in this manner immediately upon start? I ran the system for a cumulative of 12-18 hours, maybe more, prior to any problems at all.

[Gary]

Missing from your data are the entering and leaving air/water temperatures.

Another reason for high superheat might be unusually heavy load... something that might reveal itself in the missing data.

[Gary]

New Specs observed

Subcooling : 50F
Superheat : 20 - 35F (rapidly oscillating)
Discharge Temp : 170F and climbing
Liquid Line Temp : 70F (100 !!! Delta T)
Discharge Pressure : 320 PSI
Suction Pressure : 5-8 PSI with random hunting in that range


Exactly what delta-T are you referring to?

320 psi translates to about 120F. With 90F air entering the condenser this would be about right, but with 50F entering air it would be very high. We need the entering and leaving air temps.

[Gary]

Why does this system have an oil separator? Seems like an unnecessary complication, especially for an unproven system. Perfect the design then add the separator if and only if it is absolutely necessary.

Exactly where is the separator injecting the oil? On a rotary compressor, the crankcase is on the high side. That's why the bottom of the compressor runs hot.

[mikeref]

QUOTE: At some point, something changed.

Quote: I removed the bulb from the suction line. I activated the system again. I squeezed lightly with my palm, the valve opened. I put it in a cup of ice, it closed up.
---------------
Nice to see the Jedi Master has returned.:)

(Pause)...Taking a different approach to the 2 quotes i brought here.
Could OP elaborate on the second Quote. "The valve opened." Did the suction pressure return to 15 PSI or higher? (As this is your base line for previous tests.)
If not, then it could be the result of your valve element losing pressure. This is a long shot but still worth considering.

[nike123]

I was having similar situation last spring in Libya when I, and my younger Italian colleague where commissioning provision cold-rooms at oil rig. We used nitrogen during brazing and all other steps by the book. One (of 5) circuits has developed restriction at filter drier which was not measurable and noticeable with regular tools we have there. After some discussion and measuring, I proposed to change filter drier since that is about 2 min. of work (flared joints). My colleague has having doubts. But after filter change everything was back in normal operation. No more high superheat and subcooling!

If you use new or used components, that doesn't mean that they are clean inside and POE oil is very effective detergent. After some time, all residual dirt and moisture finish its trip through system, and ends up where it is belongs. In Filter-drier!

Therefore, I would, without much over-thinking (maybe 30 sec maximum), after system assembly, and system is developed restriction or even look-like restriction, change that filter drier, no matter what!

And, if I doing that for myself, I would change it after 2-3 days even without that symptoms, just to lower possible moisture content in system below 10 ppm. It helps in system longevity.

That system is not domestic fridge with critical charge of 40g of refrigerant, and I don't see necessity to place there brazed filter drier (if it is).

Z=x+4y
X is solved (no more uknown)!;)
Lets move to Y!:D

[mikeref]

Sometimes the drier is defective before delivery. A C-032...is basically a small fecker for pilot duties, or small commercial work and is good for limited liquid flow like capillary systems. Up sizing to an 052 or a 082 1/4 inch drier won't be a problem on your TX valve system.

[Gary]

Nice to see the Jedi Master has returned. :)


Nice to be back. Had some health problems last year... but have since recovered. :)

[Gary]

Sometimes the drier is defective before delivery. A C-032...is basically a small fecker for pilot duties, or small commercial work and is good for limited liquid flow like capillary systems. Up sizing to an 052 or a 082 1/4 inch drier won't be a problem on your TX valve system.

Also, ideally the drier should be mounted vertical with the flow downward. This helps ensure liquid at it's outlet.

[Jova007200]

Exactly what delta-T are you referring to?

320 psi translates to about 120F. With 90F air entering the condenser this would be about right, but with 50F entering air it would be very high. We need the entering and leaving air temps.

Well, I probably wasn't using the lingo exactly.... I was referring to the temperature from the discharge peak to the condenser outlet.

The discharge gas was superheated significantly given the high differential and already high superheat hitting the suction inlet. The discharge line kept heating and it was at 170F when it cut off. The liquid line just prior to that event was at 70F. That was what I meant when I said delta T.

Condenser Water Inlet : 80F
Condenser Water Outlet : 87-88F

I'd take another reading, but as it sits without refrigerant........... I'd be more comfortable with its accuracy if I could.

* * * *

The Coolant delta T from chiller inlet to outlet is roughly 8F average through the range. It is as high as 10F when the reservoir temperature is above 60F and as low as 5F when the reservoir temp reaches single digits.

Ex. When the Coolant Inlet is 11F, the outlet is between 5 - 6F.

I'll admit, these values are not from the problematic operation.

* * * *

As far as dirty components, I would not be surprised if this was merely a result of start up grime plugging the Drier..... Some of the crap I've seen in manufacturing..... "World Class" manufacturers too...

* * * *

I added an oil separator after somebody made the suggestion. I guess his reasoning was that it would improve efficiency. I didn't have any real reason to doubt his advice.

Shall I just remove it? Would certainly have no problem with that. Plus, I think I can find a use for that valve as it is.

[install monkey]

a heavy wallet can affect circulation to the legs!;)
good to see ya gary

Nice to be back. Had some health problems last year... but have since recovered. :)

[Gary]

If the condenser inlet water is 80F, then how can the liquid line temp be lower than 80F?

[Gary]

a heavy wallet can affect circulation to the legs!;)
good to see ya gary

A plugged artery can affect the circulation even more.

[Jova007200]

If the condenser inlet water is 80F, then how can the liquid line temp be lower than 80F?

I don't know. Doesn't make sense does it. Magic! :)

And I've just embarrassed myself... It happens. Thanks for catching it.....

I posted the normal system range, because I edited my post to add it after I read through and the last numbers I focused on were the Cooler values under normal conditions. So I posted from memory while I was thinking of that and somehow it just felt "right."

Obviously, that's physically impossible. The inlet temperature to the condenser wasn't taken. The outlet was taken, and it was near the same temperature as the refrigerant.

[Gary]

When I make mistakes I blame it on the meds. :)

[nike123]

...........................:o

[Gary]

With a counterflow or crossflow condenser, we might expect a small temperature difference between the entering water and the leaving refrigerant. If there were an insulative coating between them (oil logged?) interfering with the heat transfer, that temperature difference might be greater... giving us an important clue.

[Jova007200]

There wasn't any indication that there was a great temperature difference at the water inlet. Although, the palm test doesn't exactly apply. I didn't take a direct reading, but the temperature difference was not thought to be substantial given the temperature of the leaving water and the filter drier (which registered with the same temp reading as the outlet just behind it).

I know that isn't exactly the scientific approach....

[Gary]

We can't see it from here. In an online venue, all we can go by are the description and the numbers. The more data the better.

[Gary]

Low side:

Evap water in
Evap water out
Suction line temp
Saturated suction temp/pressure

High side:

Cond water in
Cond water out
Liquid line temp
Saturated cond temp/pressure

[Magoo]

Hi Gary,

good to see you back on the forum.

[Jova007200]

Low side:

Evap water in
Evap water out
Suction line temp : -8 (approx)
Saturated suction temp/pressure : -35

High side:

Cond water in : Unsure (I don't trust my memory quite enough)
Cond water out : 70F (approx)
Liquid line temp : 69 - 70F
Saturated cond temp/pressure : 120/315



I added what I could. I don't have the cooler inlet/outlet temps, though the progression from 60F to 0F was markedly faster for the glycol coolant.

[Jova007200]

I should mention that suction line temp varied given the hunting that was occurring at this point. -8 is probably a fair minimum temp.

[Jova007200]

o.O suction pressure approximated near 7PSI avg.... its getting later, I'm omitting things.... eck...

[Gary]

Additional Info :

The system uses an oil separator. Initially, I had its oil drain controlled by a solenoid valve on a delay cycle that only ran once per running cycle. I decided that I botched that badly and changed to a on/off repeat delay. It also pumps down at the end of each cycle for an unloaded start via the thermostat controlled solenoid on the liquid line. Compressor is controlled by low pressure switch.


Why is there a solenoid in the oil return line? I'm wondering if that might cause the separator to act as a condenser/receiver, storing liquid refrigerant... to be unleashed on the system periodically, overfilling and possibly oil logging the condenser? The hunting might be oil working its way through the orifice in short spurts.

[Jova007200]

Why is there a solenoid in the oil return line? I'm wondering if that might cause the separator to act as a condenser/receiver, storing liquid refrigerant... to be unleashed on the system periodically, overfilling and possibly oil logging the condenser? The hunting might be oil working its way through the orifice in short spurts.

Just following manufacturer EBs. The receiver doesn't have a float valve or any type of release within. Oil return could be controlled through a capillary line or a solenoid valve. I chose the solenoid option. The solenoid port is 3/32.

I was considering the possibility that the original relay setting (one on/off cycle) may have allowed too much oil to collect in the separator, causing it to blow out into the system. It would only open during start up, and never again until the next start up. (I know, stupid) The cycle was changed [prior to the problem showing up] to a repeat on/off cycle.

The separator temperature during operation was consistently above the saturation temp. The check valve down stream protected it from back flow upon deactivation. The solenoid valve has always opened at start-up for a few seconds as well, regardless of the cycle chosen.

The hunting was cyclical. It did not appear to be very random. I really felt that it was responding to the bulb conditions.

That said, I did not insulate the separator to protect from off cycle condensing. I considered the check valve and limited amount of refrigerant in that part of the system to be insufficient to cause a problem. I asked an HVAC engineer friend of mine at work if he thought it would be necessary, and he suggested that it was not given the application. So I didn't. Whether or not that was an error on my part is beyond me.


Would you recommend just removing the separator from the equation to negate the possibility you are suggesting?

[Gary]

Yes... I would remove the oil separator. It is highly unlikely that this system would need an oil separator.

[Jova007200]

Agreed.

So, this is what I'm going to do.


Change the TXV Element
Remove Oil Separator
Change Filter Drier


As far as other components, I'm going to hold off on that for now. Given that the TXV can be isolated I'm going to hold off on that for now.

Is this a fair assessment at this point?

[Gary]

Just following manufacturer EBs. The receiver doesn't have a float valve or any type of release within. Oil return could be controlled through a capillary line or a solenoid valve. I chose the solenoid option.

I've never dealt with a separator that didn't have a float. Must be something new. Seems like it could condense liquid refrigerant... and the oil would float on top of that liquid.

[Gary]

Agreed.

So, this is what I'm going to do.


Change the TXV Element
Remove Oil Separator
Change Filter Drier


As far as other components, I'm going to hold off on that for now. Given that the TXV can be isolated I'm going to hold off on that for now.

Is this a fair assessment at this point?

Sounds like a plan. :)

You might also want to check the pressure/temperature correlation of the recovered refrigerant... just in case.

[Jova007200]

I've never dealt with a separator that didn't have a float. Must be something new. Seems like it could condense liquid refrigerant... and the oil would float on top of that liquid.

Perhaps it should have been a clue when I couldn't find a separator that was properly sized that HAD a float. :)

Thanks for all of the advice. :)

[Gary]

You are quite welcome. When you get it going be sure to gather a full set of data so we can evaluate and fine tune the system. You might also find the following link helpful:

http://www.refrigeration-engineer.com/forums/showthread.php?19701-Refrigeration-101&p=151598#post151598

[Jova007200]

I'll surely do that.

One thing, though. It was suggested that I get an element with a MOP charge. I cannot find any 507 elements with such a charge; only for 404a.

Am I missing something?

[Gary]

The purpose of the MOP charge is to protect the compressor from overloading when subjected to heavy loads. Will this system be subjected to heavy loads?

R507 and R404a are very similar. Essentially if you take R507 and add a small amount of R134a, you have R404a.

[Jova007200]

Indeed. I just wasn't sure if it would be an issue if I had to go with a 404a with a MOP Charge if needed.

The most that I would expect the load on the coolant to be is around 1200 Watts. Average load would likely be much less, with a practical maximum of about 1kw.

[Gary]

If the compressor isn't straining (high amps, kicking out on overload, etc.) during pulldown from room temperature, then I wouldn't bother with the MOP charge. Pulldown is the heaviest load, but the loading is limited by orifice size and surplus charge.

Actually, I have yet to see any evidence of a TXV problem.

[Jova007200]

I came to a similar conclusion after the TXV bulb responded to my hand and to a cup of ice. Though, would it be prudent to change to a Z charge given that the C only really controls SH reliably down to -10F or so.

Or is that really not a big deal?

[Gary]

Are you planning on running your glycol down below -10F?

[Jova007200]

Not likely.

So I'll interpret that as a negative regarding the need for a Z charge.