walk in freezer icing after expansion valve

[indoorairpro]

When I arrived discharge temp from evap was about 10 degrees.
everthing after expansion valve frosted over.
Sight glass was not clear
outside ambient temp about 20 degrees
only one condensor fan running due to ambient temp
cond labeled R404A but there is possibility of mixed refrigerants according to owner
low psi 3 lb high around 150 and sub cooling to low to read accurately.
Since I knew siht glass should be flooded wspecially with such low ambient temps I added some 404a.
low only rose to about 5 lbs high rose to about 250 and sub cooling also went up to about 15 degrees
Discharge temp in box droped to about 10 degrees and sight glass was still bubbling although not as much.

At this point something happened between my boss and owner I guess about price so I was asked to pack up and leave but was wondering what you veterens would have done next and if you had to guess what would you think the problem was.

Also did put into defrost and defrost cyle was working although there did not seem to be any type of pumpdown. Condensor just turned off when t went into defrost.

Thaks in advance for your response

[2sac]

Wht shouldn't a freezer ice up after the valve? Sounds like you have other issues. We need more info before proceeding.

[indoorairpro]

Understood but I was not there long enough to collect any other data and generally dont spend much time working on freezers. I would expect some frost after expansion valve but is solid ice normal? wouldnt defrost cycle knock that down?

again was not looking for an answer just some general opinions. More interested in why high side was high but still had bubbles in sight glass. If expansion valves was closeing for any reason plugged, broken overcharged whatever , would that not cause sight glass to clear even faster as liquid backed up to condensor?

[KB Cool]

Your low side pressure too low for a freezer running 404a. Is your dryer before or after sg?

[jpsmith1cm]

Sight glass was not clear

You need to remedy this first.

[bunny]

low psi 3 lb high around 150 and sub cooling to low to read accurately.

Seriously????

I would love to hear an explanation on the sub cooling being too low to measure accurately.

[cavalieri85]

Step1 if mixture of refrigerants is suspected than before anything else recover, change drier, evacuate and recharge.

[Navy06]

If I was told there may be mixed gas in system I would have pulled the charge and also changed out FD on system. also after the txv there could be moisture in the system causing the ice up on the lines. next step would have been to do an efficiency test on the comp.

[malcor]

If I was told there may be mixed gas in system I would have pulled the charge and also changed out FD on system. also after the txv there could be moisture in the system causing the ice up on the lines. next step would have been to do an efficiency test on the comp.

I'm curious, do you actually repair commercial refrigeration equipment?

Don't mean to be rude but your recommendations, and a couple of others, really has me wondering...

[indy2000]

txv and feeds freezing..........is normal in LT.

Some of our bigger MT evaps even show frosting at times...dew and freezing point.

I think when you mentioned subcool is too low to measure, you meant there was NO subcooling, as you indicated the sight glass was flashing.

As mentioned you need to establish solid liquid to txv, and then measure SH from the evap.

From there you can make other judgement calls..........but seeing you got called off, its obvious the customer is looking for cheap and dirty fix.

Look at the TXV label to see what possible refrigerant is in the system.

[cavalieri85]

It doesn't matter what the system is doing as long as he has a zcontaminated system with mix of refigerants this unit won't work

[malcor]

It doesn't matter what the system is doing as long as he has a zcontaminated system with mix of refigerants this unit won't work

Customers can sometimes provide useful information or clues. In this example the customer said that there was a possibility of mixed refrigerant. That information may or may not be helpful, depending on what information they are basing that assessment on.

At what point would you step back from changing parts and actually diagnose the fault?

[cavalieri85]

Well with an erratic system and only having limited info given to me at this point. Eliminating any possibility of mixed gases seems a good option. Of course looking at my superheat subcool comp amps and performance of system are a prerequisite to my suggestion. I am confused about what you are suggesting. Of course I would diagnose the unit!! Usually when a customer says this may have happened means it definitely did

[ryan1088]

Well with an erratic system and only having limited info given to me at this point. Eliminating any possibility of mixed gases seems a good option. Of course looking at my superheat subcool comp amps and performance of system are a prerequisite to my suggestion. I am confused about what you are suggesting. Of course I would diagnose the unit!! Usually when a customer says this may have happened means it definitely did

One would have to at least inquire further how he knows the refrigerant is mixed?

[malcor]

Well with an erratic system and only having limited info given to me at this point. Eliminating any possibility of mixed gases seems a good option. Of course looking at my superheat subcool comp amps and performance of system are a prerequisite to my suggestion.

You are right in the limited amount of information. One of the most useful tools you possess is your powers of observation, and that is something that can’t be substituted for in a remote diagnosis.

I am confused about what you are suggesting. Of course I would diagnose the unit!! Usually when a customer says this may have happened means it definitely did

I suppose everyone has a different method of diagnosis. Okay, I’ll play this game. Lets diagnose this system for fun!

First of all, customers can provide useful information. However, they also have a propensity to volunteer misleading and useless information too. I personally don’t place the importance any relevant information from a customer above my own judgment.

One of the standard questions that I usually ask is ‘when they noticed the fault occur’ (in this instance, the temperature becoming warmer). The answer is often relevant later in the diagnosis. Eg. if the fault turns out to be a leak, the size of the leak can be approximated by the duration and intensity of the symptoms.

If a customer said that they thought there were a possibility of mixed/contaminated refrigerant then I would have immediately asked them to elaborate on it. Sometimes answers can be surprising... “Three years ago it had a gas leak and the guy who came out was trying to figure out what gas it took. So he may have put the wrong gas in, but it’s been working good since he fixed it until the other day”

It would be unwise to dismiss the customers claim so we’ll entertain the possibility of there being contamination of the refrigerant. According to the OP the system is performing as follows: (I'm including metric because that's what I am most familiar with)

Refrigerant: R404a
Evap. Discharge Temp: 10’F (-12.2’C)
Suction pressure: 3psi (21kPa)
Discharge Pressure: 150psi (1034kPa)
SST: -44.6’F (-42.6’C)
SDT: 70.1’F (21.2’C)
Outside Air Temp: 20’F (-6.7’C)

Observations: Frosting/ice between TXV and evap. Refrigerant bubbling through sight glass.

Action taken: Initiated defrost cycle. Added refrigerant R404a to system.

Resultant change to system operation:

Evap. Discharge Temp: 15’F (-26.1’C)
Suction pressure: 5psi (34kPa)
Discharge Pressure: 250psi (1724kPa)
SST: -40.3’F (-40.2C)
SDT: 103.8’F (39.9’C)
Refrigerant still bubbling through sight glass but not as much.

From the above, it should be clear that the evaporator is starving of refrigerant. The bubbles through the sight glass are likely a result of the lack of load on the system and the resulting lower volume of the refrigerant due to the outside ambient conditions. It was most likely a little undercharged as well.

We can rule out the system being low on refrigerant at this point. If it were low on refrigerant then the sight glass would have to be just about empty of liquid for the suction pressure to be at 5psi with the TXV wide open with a discharge pressure of 250psi.

Okay, so let’s entertain the claim of refrigerant contamination...

What would the TXV do if R134a, R22 or even both were mixed with R404a?

At a suction pressure of 5psi the temperature at the TXV sensor would have to be about -40’F for it to be throttling back. The saturated temperature of R134a at 5psi is -3.5’F and R22 is -30’F. It would have to have a mix of R410a (-50.3’F) before the TXV would throttle back and in that case the evap discharge temp would be lower than measured not to mention the discharge pressure.

So if there were significant refrigerant contamination then the symptoms presented would be different. The refrigerant would be flooding back to the compressor and the suction pressure would be much higher. There may still be contamination of the refrigerant but it would not be the cause of the current failure condition.

So we can rule out refrigerant contamination for now.

What else?

Clearly there must be an issue with the TXV. At this point I would have measured the superheat (which would no doubt be very high) and adjusted the TXV to confirm that the problem is with it. The power element is probably losing its charge so would require a new TXV.

If the superheat measurement was okay then the problem would most likely be with the CPRV. However, considering the symptoms I would say the fault was with the TXV.

[cavalieri85]

Malcor
With all that said and the data given i would have to say I would agree with you. But am curious about a few other ideas. What is the placement of the txv sensing bulb. How is it strapped did the guy that installed it zip tie it to the bottom of the suction line? What type of valve is it? Pressure limiting maybe? Does this unit have a CPR? Is the coil clean or filthy? Could something like hp 80 be in the unit? Is there a fan cycle control? Is it working? I live in south Florida so diagnosing units that operate in a cold climate is a foreign idea to me. It was 87 degrees here yesterday. We have 2 seasons hot and hotter and humid.

[malcor]

But am curious about a few other ideas. What is the placement of the txv sensing bulb. How is it strapped did the guy that installed it zip tie it to the bottom of the suction line? What type of valve is it? Pressure limiting maybe? Does this unit have a CPR? Is the coil clean or filthy? Could something like hp 80 be in the unit? Is there a fan cycle control? Is it working?

I agree with you on all of the above. We can only go by what information the OP provides us, which in his view would be all the relevant information pertaining to the fault. Any other system attributes would be considered as being normal to them and not worth mentioning. Assuming anything more about the system on our part will just make the diagnosis less accurate.

Also, we should assume that the system was working and then there was a breakdown situation. If it were a chronic fault then the OP surely would have mentioned it…

I live in south Florida so diagnosing units that operate in a cold climate is a foreign idea to me. It was 87 degrees here yesterday. We have 2 seasons hot and hotter and humid.

I live in Sydney, Australia. Today it was about 86'F and in winter 41'F would be considered extremely cold! However, I work on systems that use chilled water in a building for cooling condensers, so am familiar with the effect of over condensation of refrigerant.

[ryan1088]

Malcor
With all that said and the data given i would have to say I would agree with you. But am curious about a few other ideas. What is the placement of the txv sensing bulb. How is it strapped did the guy that installed it zip tie it to the bottom of the suction line? What type of valve is it? Pressure limiting maybe? Does this unit have a CPR? Is the coil clean or filthy? Could something like hp 80 be in the unit? Is there a fan cycle control? Is it working? I live in south Florida so diagnosing units that operate in a cold climate is a foreign idea to me. It was 87 degrees here yesterday. We have 2 seasons hot and hotter and humid.

I hate you right now, just sayin'. I'd love to be down there with that!

[Tommy knocker]

Have to pull charge and replace drier evacuate and charge with correct refrigerant before any diagnostics can be attempted. No data can be trusted at this point and is therefore useless. Right now we don't know what the SST, SCT are.

[malcor]

Have to pull charge and replace drier evacuate and charge with correct refrigerant before any diagnostics can be attempted. No data can be trusted at this point and is therefore useless. Right now we don't know what the SST, SCT are.

I disagree. Even mixed/contaminated refrigerant can be diagnosed.

If you have a proper understanding of the fundamentals of refrigeration and how the various components function then you can diagnose without first changing parts. The diagnosis may require stages where parts are changed but not where parts are changed prior to making a diagnosis.

Eg. Diagnose faulty/locked compressor. Install new compressor. Run system then identify cause of compressor failure - improperly secured TXV sensor.