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tjcsf07
03-19-2016, 07:14 PM
All,

I am looking for some help working on a small walk-in freezer. It's somewhat of a bastardized set up with a trenton Teha-025 (404a) condenser mounted outdoor on the roof (roughly 10' above the box) and a russel ae26-92 two fan evaporator, electric defrost.

Let me start by saying my experience with refrigeration is limited to what I learned at the voc-tec in high school. I did stay in the field long enough to get a technicians license in MA, but for the most part I only worked on comfort cooling equipment.

These days I am a project manager for a decent sized mechanical contractor so I do not break out the tools very often anymore.

The equipment in question was existing in a space that that a friend of mine acquired to expand his restaurant business into, there is no service history available for the walk in freezer.

We powered on the freezer when he moved into the space last summer and the box pulled right down to temp and pumped itself down. Other than a quick check of the coils to see if we needed to clean anything up, I did not observe the operation of the freezer for more than an hour or so or however long it took to pull down.

The first cool night that fall, I was called to check out the box as it had gone warm for a few hours. I stopped by after work and observed bubbles in the sight glass (it was still cool out)...blocking off the condenser with cardboard cleared the glass and the box quickly pulled down.

A few days later I had some time to investigate what was happening with the machine. With the cardboard still on the condenser, the head pressure was keeping within a few #'s of the 210# the headmaster is supposed to be maintaining.

I took the cardboard off and weighed in enough refrigerant to clear the sight glass (ended up being just under 2lbs). I didn't record any other data at that time but the box maintained temperature from that point in the fall all the way through the winter (through a cold snap with some -5 ambient temperatures) until just the other day.

Now the box will not maintain temperature and I am experiencing flood back to the compressor. Head pressure sits right at 200# and suction at 40-45# - with a 40 degree box temperature I was expecting the elevated suction pressure. Here is the odd part, the evaporator has no frost on it at all but the suction line frosts all the way back to the compressor starting just past the txv equalizer line. Just prior to the equalizer connection the evaporator temperature was about 30 degrees.

Suspecting i had inadvertanly overcharged the unit in the fall, I pumped it down and torched the reciever...I found the charge to be roughly 75 percent of the reciever. (Reciever capacity is 16lbs).

Out of frustration, I recovered the entire charge (13lbs) and started weighing in virgin 404a until the sight glass cleared. Still I ended up with a 40 degree evaporator, and low superheat at the compressor (less than 10 degrees). As much as i didnt want to fool with adjusting the TXV, I had begun to suspect it was flooding to the point that all of my refrigerant is boiling in the suction line instead of the evaporator. Perhaps a bad sensing element?

Increasing the superheat adjustment of the valve (yes the bulb is properly secured and insulated) did not have any effect on suction superheat at the compressor, however going to the other extreme of adjustment on the txv resulting in the four distributer lines staring to frost and the the first few return bends of the evaporator coil were beginning to show frost...but then the compressor started to get slugged with liquid.

Because I have more money than brains, I decided to replace the TXV, even though I had not completely proved that it was the culprit.

The new valve had no effect on the trouble.

Today I spent some more time troubleshooting. I recovered the full charge. This time I weighed in only 6 lbs and started adding slowly while watching superheat at the compressor. Still I am getting only 10-12degrees SH at the compressor and very little if any cooling out of the evaporator.

At this point the only thing that is clear to me is that the evaporator is not absorbing heat, which is resulting in the flooding and low compressor SH.

Is the evaporator oil logged or something?

Any thoughts are welcome.

http://images.tapatalk-cdn.com/16/03/19/0c8c2831c5bc48d3353eac251d3e3629.jpg

http://images.tapatalk-cdn.com/16/03/19/389055aa6c437d2b45c2d49a3940a83d.jpg

http://images.tapatalk-cdn.com/16/03/19/ba91ad0e40f2530650f2ffdbaf1c6f73.jpg

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TechmanTerry
03-19-2016, 07:41 PM
Project Manager these days? And you're in the trenches?

kamersoutdoor
03-19-2016, 07:42 PM
Are you checking superheat readings at the evap outlet?
You'll need to start there!

kamersoutdoor
03-19-2016, 07:46 PM
Check at the outlet of the evap before the suction line heat exchanger (subcooler)
My guess is pretty close to zero.... crank the puppy in

tjcsf07
03-19-2016, 07:51 PM
Techman- I am just trying to help out a friend

Kamers- agreed. getting the superheat in order at the evaporator outlet is the goal, however I am clearly not even in the ballpark (see photo).

The dissertation I wrote probably didn't explain very well, but adjusting the txv didn't really get me too far....cranking it way in and I'm still only boiling in the suction line....back it out two turns or so past the middle and I get some boiling in the evaporator but then i start slugging


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VTP99
03-19-2016, 08:09 PM
What do you mean you start "slugging" ? At 1* superheat you shouldn't be.

TechmanTerry
03-19-2016, 08:11 PM
OK Brother, put the TXV SH stem "dead center". TENDERLY, LOVINGLY,PROPERLY.

BALloyd
03-19-2016, 08:12 PM
I'll bet you have an internal high to low leak on the subcooler.

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tjcsf07
03-19-2016, 08:21 PM
Techman- the photos were taken after I put the valve back in the mid range...within a quarter turn.

BALloyd- can you help me understand your thought process on the failed subcooler?

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BALloyd
03-19-2016, 08:24 PM
Liquid refrigerant is leaking from liquid line directly into suction line post evaporator, sending liquid back to compressor.

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BBeerme
03-19-2016, 08:33 PM
40-45# suction with 404a puts the evap at 5-10*F. Do you have airflow through the evap? I've seen evaps frozen in the middle, so you couldn't easily tell just by looking.



All,

I am looking for some help working on a small walk-in freezer. It's somewhat of a bastardized set up with a trenton Teha-025 (404a) condenser mounted outdoor on the roof (roughly 10' above the box) and a russel ae26-92 two fan evaporator, electric defrost.

Let me start by saying my experience with refrigeration is limited to what I learned at the voc-tec in high school. I did stay in the field long enough to get a technicians license in MA, but for the most part I only worked on comfort cooling equipment.

These days I am a project manager for a decent sized mechanical contractor so I do not break out the tools very often anymore.

The equipment in question was existing in a space that that a friend of mine acquired to expand his restaurant business into, there is no service history available for the walk in freezer.

We powered on the freezer when he moved into the space last summer and the box pulled right down to temp and pumped itself down. Other than a quick check of the coils to see if we needed to clean anything up, I did not observe the operation of the freezer for more than an hour or so or however long it took to pull down.

The first cool night that fall, I was called to check out the box as it had gone warm for a few hours. I stopped by after work and observed bubbles in the sight glass (it was still cool out)...blocking off the condenser with cardboard cleared the glass and the box quickly pulled down.

A few days later I had some time to investigate what was happening with the machine. With the cardboard still on the condenser, the head pressure was keeping within a few #'s of the 210# the headmaster is supposed to be maintaining.

I took the cardboard off and weighed in enough refrigerant to clear the sight glass (ended up being just under 2lbs). I didn't record any other data at that time but the box maintained temperature from that point in the fall all the way through the winter (through a cold snap with some -5 ambient temperatures) until just the other day.

Now the box will not maintain temperature and I am experiencing flood back to the compressor. Head pressure sits right at 200# and suction at 40-45# - with a 40 degree box temperature I was expecting the elevated suction pressure. Here is the odd part, the evaporator has no frost on it at all but the suction line frosts all the way back to the compressor starting just past the txv equalizer line. Just prior to the equalizer connection the evaporator temperature was about 30 degrees.

Suspecting i had inadvertanly overcharged the unit in the fall, I pumped it down and torched the reciever...I found the charge to be roughly 75 percent of the reciever. (Reciever capacity is 16lbs).

Out of frustration, I recovered the entire charge (13lbs) and started weighing in virgin 404a until the sight glass cleared. Still I ended up with a 40 degree evaporator, and low superheat at the compressor (less than 10 degrees). As much as i didnt want to fool with adjusting the TXV, I had begun to suspect it was flooding to the point that all of my refrigerant is boiling in the suction line instead of the evaporator. Perhaps a bad sensing element?

Increasing the superheat adjustment of the valve (yes the bulb is properly secured and insulated) did not have any effect on suction superheat at the compressor, however going to the other extreme of adjustment on the txv resulting in the four distributer lines staring to frost and the the first few return bends of the evaporator coil were beginning to show frost...but then the compressor started to get slugged with liquid.

Because I have more money than brains, I decided to replace the TXV, even though I had not completely proved that it was the culprit.

The new valve had no effect on the trouble.

Today I spent some more time troubleshooting. I recovered the full charge. This time I weighed in only 6 lbs and started adding slowly while watching superheat at the compressor. Still I am getting only 10-12degrees SH at the compressor and very little if any cooling out of the evaporator.

At this point the only thing that is clear to me is that the evaporator is not absorbing heat, which is resulting in the flooding and low compressor SH.

Is the evaporator oil logged or something?

Any thoughts are welcome.

tjcsf07
03-19-2016, 08:35 PM
Liquid refrigerant is leaking from liquid line directly into suction line post evaporator, sending liquid back to compressor.

Sent from my SM-N910W8 using Tapatalk
That could explain why I have to wind the TXV all the way open to get any appreciable cooling out of the evap. And why the new TXV reacted exactly the same as the one it replaced.

Seems to me I could just bypass the liquid line across the subcooler then and pinch off/braze the inlet & outlet.

I did notice before I added the flooding charge back in the fall that the gas was really screaming through the evaporator.....so maybe that "wore out" the subcooler?

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VTP99
03-19-2016, 08:35 PM
Close the LLSV, after it pumps down if your suction starts to rise good chance BALloyd has it right.

TechmanTerry
03-19-2016, 08:50 PM
Stuck WIDE open TXV, no guts in TXV?

Would a leaking subcooler backfeed into the evap enough to frost the bottom of the evap? Or is it 50/50, partially feeding thru evap? A couple of digital thermometers would confirm,yes?

tjcsf07
03-19-2016, 08:54 PM
40-45# suction with 404a puts the evap at 5-10*F. Do you have airflow through the evap? I've seen evaps frozen in the middle, so you couldn't easily tell just by looking.
Bbeerme...I think this is what I was getting most stuck on also....my gauges were telling me I had a frosty coil but I had barely refrigerant feeding into it. I put my pipe clamp on all of the return bends, felt the coil up and down there was no part of it that was below 40. But right at the outlet it had a very definitive frost line.

I may be a PM / office dweeb, but I had (or thought i had) a pretty solid understanding of basic refrigeration going into this one...[emoji53]

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tjcsf07
03-19-2016, 09:11 PM
Close the LLSV, after it pumps down if your suction starts to rise good chance BALloyd has it right.
Thank you for the insight.

The only time I have pumped this one down with my gauges on it was via the king valve...the pressure only crept up once and then it held there for a good long while....so I can assume relatively tight compressor valves.

But by pumping it down via the LLSV, I will keep the liquid pressure on the subcooler and and it should show up on my low side gauge pretty clearly.

You da man!

Probably would have taken me weeks to come up with that thought.

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Mike19
03-19-2016, 09:15 PM
I'll bet you have an internal high to low leak on the subcooler.

Sent from my SM-N910W8 using Tapatalk

+1

That is my first thought also

yaytech
03-19-2016, 09:15 PM
check suction line temp in and out of heat exchanger...

tjcsf07
03-19-2016, 09:39 PM
+1

That is my first thought also
Clearly I came to the right place with my question.

Actually, I think I recall reading about someone on here discovering this happening to a system they were working on a while back....

I will do the pump down test and let you guys know what I find.



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TechmanTerry
03-19-2016, 09:43 PM
VTP99, Good call.Makes sense.

Galt
03-19-2016, 09:53 PM
After you remove it let us know the results

VTP99
03-19-2016, 10:03 PM
I believe the credit is do to BALloyd ;)

tjcsf07
03-19-2016, 10:05 PM
After you remove it let us know the results
Should the pump down test point me in that direction, do I really need to remove it? My first thought is to just bypass it then pinch off the inlet and outlet and braze it shut.

Does anyone think a subcooler on such a small unit is even necessary in the northeast?

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VTP99
03-19-2016, 10:16 PM
Does anyone think a subcooler on such a small unit is even necessary in the northeast?

If the liquid line passes thru a hot attic where it could flash, then yes. Otherwise your bypass would be fine. I don't see to many HX'ers on w/i freezers in NE Ohio.

lytning
03-20-2016, 06:42 AM
I have got rid of a few.

Should the pump down test point me in that direction, do I really need to remove it? My first thought is to just bypass it then pinch off the inlet and outlet and braze it shut.

Does anyone think a subcooler on such a small unit is even necessary in the northeast?

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Rhinohead
03-20-2016, 11:46 AM
How many fans? Rotation correct ?

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TechmanTerry
03-20-2016, 12:21 PM
Did you look for the "round orifice disk" in the copper feeding into the distributor, ? Can you test for pressure in the TXV "equalizer" line on the TXV body, at that 1/4 SAE nut? What does the "frost pattern" look like on the other end of the evap coil?

tjcsf07
03-20-2016, 12:33 PM
I believe the credit is do to BALloyd ;)
Thank you Gentlemen.

BALloyd was right on the money.

http://images.tapatalk-cdn.com/16/03/20/500809eecedb6115c99ea938ac29e752.jpg

http://images.tapatalk-cdn.com/16/03/20/5bc8490401a64961ce897836c678fc3e.jpg

http://images.tapatalk-cdn.com/16/03/20/f9d381e548f0710f6a0bcf2a19590912.jpg

http://images.tapatalk-cdn.com/16/03/20/c49ea73e43d96877b0860494e6bfd4a5.jpg

Thanks again for the help, I can go back to my desk now and let you guys have all the fun ones to fix.

[emoji481] [emoji481]

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VTP99
03-20-2016, 12:40 PM
Thanks for the followup and a job well done .

tjcsf07
03-20-2016, 12:40 PM
I had meant to comment on the picture of the manifold....when trying to pump down via LLSV, it was bypassing so quickly could only get it to pull down to about 10# suction.

The picture was taken about 10s after I threw the disconnect...it must have been decent sized rupture inside that HX

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TechmanTerry
03-20-2016, 12:48 PM
Congrats! As usual ,I learned something.

BALloyd
03-20-2016, 01:00 PM
Your welcome. Glad you got it fixed.

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lytning
03-20-2016, 01:08 PM
Don't forget to replace end cover on TXV.

tjcsf07
03-21-2016, 08:17 AM
Don't forget to replace end cover on TXV.

I had intentionally put my wrenches in my back pocket so I would not forget to go back into the box and button up the TXV.

Sure enough, I packed up all of my tools hopped in my truck and was about to head home when I felt the wrenches in my pocket and remembered that I still needed to put the stem cap on.