walk in freezer icing after expansion valve

[Tommy knocker]

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.

I understand and if this were a mechanical failure or unit would not run, start, or pump then some diagnosis could be done prior to pulling charge. But in this case it does start, run, and pump and is having a lack of cooling issue. Therefore system data is needed to trace problem to its source. Charge must be corrected to ensure accurate data.

[air1]

Malcor,
Could fractionation be a possible problem?

[malcor]

I understand and if this were a mechanical failure or unit would not run, start, or pump then some diagnosis could be done prior to pulling charge. But in this case it does start, run, and pump and is having a lack of cooling issue. Therefore system data is needed to trace problem to its source. Charge must be corrected to ensure accurate data.

First of all, the OP stated that the owner said that there were 'a possibility of mixed refrigerant' in the system. No other information in regard to that was given by the OP.

So there may or may not be an issue of refrigerant contamination.

However, there is valid system data that could be measured to substantiate the claim of refrigerant contamination being the cause of the problem.

That data is:

Suction Pressure
Discharge Pressure
Temperature at the TXV sensor

The expected refrigerant is known, R404a.

Knowing how a TXV works, I could determine if the problem was due to refrigerant contamination, and so should you.

[malcor]

Malcor,
Could fractionation be a possible problem?

In my experience with R404a I would say a definate no.

However, fractionation would be highly possible if the refrigerant was contaminated with say R407c, R410a or even any other refrigerant I suppose.

To rule fractionation out as the cause it would be a simple matter of measuring the suction pressure and temperature at the TXV sensor on this particular system. If contamination were the case I would expect the refrigerant to be contaminated with R410a.

The symptoms and measurements provided by the OP don't point to it in my opinion.

[Tommy knocker]

First of all, the OP stated that the owner said that there were 'a possibility of mixed refrigerant' in the system. No other information in regard to that was given by the OP.

So there may or may not be an issue of refrigerant contamination.

However, there is valid system data that could be measured to substantiate the claim of refrigerant contamination being the cause of the problem.

That data is:

Suction Pressure
Discharge Pressure
Temperature at the TXV sensor

The expected refrigerant is known, R404a.

Knowing how a TXV works, I could determine if the problem was due to refrigerant contamination, and so should you.

Relax Mal. Not trying to prove your wrong here. My point is in this situation the proper thing to do is pull the charge, since there is a concern of a mix. It's a variable that can and should be taken out of the equation.

[malcor]

Relax Mal. Not trying to prove your wrong here. My point is in this situation the proper thing to do is pull the charge, since there is a concern of a mix. It's a variable that can and should be taken out of the equation.

I'm not saying that by replacing the refrigerant it is the wrong thing to do either.

The reason why I joined in this discussion was because I was questioning the method of diagnosis. I don't visit this site much and the idea of changing parts without diagnosis was surprising and foreign to me. But I suppose you guys in the USA do things a little different to here. Not that it's a bad thing, just different. Much like the language, we say prawn you say shrimp!

All good and understood.

[cavalieri85]

Is fractionation as prevalent as we have been told. I know it is a real andnit fors happen but I don't know that I have ever seen a unit fail because of it.

[markettech]

First of all, the OP stated that the owner said that there were 'a possibility of mixed refrigerant' in the system. No other information in regard to that was given by the OP.

So there may or may not be an issue of refrigerant contamination.

However, there is valid system data that could be measured to substantiate the claim of refrigerant contamination being the cause of the problem.

That data is:

Suction Pressure
Discharge Pressure
Temperature at the TXV sensor

The expected refrigerant is known, R404a.

Knowing how a TXV works, I could determine if the problem was due to refrigerant contamination, and so should you.

I know how a TXV works.

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.

I also know a low temp TXV is not adjusted to achieve 0F superheat at the outlet of the coil before the valve starts throttling closed.

What blows my mind here is how you've dismissed the possibility of mixed refrigerant in the system based on nothing more than wild assumptions...with virtually zero quantifiable data to back it up.

You know how a TXV works - and with this knowledge are able to definitively determine whether or not a system is contaminated with mixed refrigerant?

Obviously I've got a lot to learn, since I don't assume the TXV is set to 0F superheat. I don't assume an evap suction outlet temperature to be 'X' based on a suction pressure reading assumed to be taken at the coil so as eliminate the possibility of a pressure drop. I gather quantifiable data and compare it to established, known values.

Someday, however - I hope to learn how evap pressure + an unknown spring pressure = contaminated refrigerant relative to an unknown push rod position.....as apparently everyone should.

If it were me, I'd be checking my LL drier, TXV inlet screen, look into the possibility of a condenser flooding valve issue....and whatever else I could think of, before haphazardly horking around with the TXV adjustment stem just for drill.


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

[2sac]

I know how a TXV works.



I also know a low temp TXV is not adjusted to achieve 0F superheat at the outlet of the coil before the valve starts throttling closed.

What blows my mind here is how you've dismissed the possibility of mixed refrigerant in the system based on nothing more than wild assumptions...with virtually zero quantifiable data to back it up.

You know how a TXV works - and with this knowledge are able to definitively determine whether or not a system is contaminated with mixed refrigerant?

Obviously I've got a lot to learn, since I don't assume the TXV is set to 0F superheat. I don't assume an evap suction outlet temperature to be 'X' based on a suction pressure reading assumed to be taken at the coil so as eliminate the possibility of a pressure drop. I gather quantifiable data and compare it to established, known values.

Someday, however - I hope to learn how evap pressure + an unknown spring pressure = contaminated refrigerant relative to an unknown push rod position.....as apparently everyone should.

If it were me, I'd be checking my LL drier, TXV inlet screen, look into the possibility of a condenser flooding valve issue....and whatever else I could think of, before haphazardly horking around with the TXV adjustment stem just for drill.


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

I agree. If there is an inclination, especially from the equipment owner, the charge is messed up, put new gas in it and remove the doubt from the equasion.

Here's the thing. In the restaurant business, most of your owners and managers who have been in the business for awhile, know what's involved in refrigeration repairs. This is why the tech not only needs to have a knowledge of his craft, but also of customer relations. The second I hear "Well, maybe this is wrong", I know someone else f'ed with it. They called me now because the guy who f'ed with it is no longer around for whatever reasons. Of course they want to save money and you will hear about it, over and over. If you fix it right they will call you back. To play guessing games with the customers money is setting yourself up to lose the customer. Be honest with them up front.

[jpsmith1cm]

Here's the thing. In the restaurant business, most of your owners and managers who have been in the business for awhile, know what's involved in refrigeration repairs. This is why the tech not only needs to have a knowledge of his craft, but also of customer relations. The second I hear "Well, maybe this is wrong", I know someone else f'ed with it. They called me now because the guy who f'ed with it is no longer around for whatever reasons. Of course they want to save money and you will hear about it, over and over. If you fix it right they will call you back. To play guessing games with the customers money is setting yourself up to lose the customer. Be honest with them up front.

There's a lot of wisdom right there.

Listen to the customer and they'll often tell you what's wrong.

[jpsmith1cm]

In my experience with R404a I would say a definate no.

However, fractionation would be highly possible if the refrigerant was contaminated with say R407c, R410a or even any other refrigerant I suppose.

To rule fractionation out as the cause it would be a simple matter of measuring the suction pressure and temperature at the TXV sensor on this particular system. If contamination were the case I would expect the refrigerant to be contaminated with R410a.

The symptoms and measurements provided by the OP don't point to it in my opinion.

How would you say that R410a can fractionate with a 0.3 degree glide yet say that 404a cannot with a 1.1 degree glide?

Either refrigerant CAN fractionate, but it isn't likely for either to do so in actual use.

[barbar]

I think if R410a is the contaminant then the mixture (If R404a was the primary) my fractionate more than say if R22 was the containment, due the bigger difference in pressure at a fixed temp.
A frosted/frozen expansion valve and distribution legs, is not at all uncommon, especially on electric defrost on pump down systems, and coil sensed defrost termination. If no pump down, less likely seen as refrigeration vapour will move back to the valve when being heat in the coil.

[ryan1088]

How would you say that R410a can fractionate with a 0.3 degree glide yet say that 404a cannot with a 1.1 degree glide?

^^^

[malcor]

I know how a TXV works.

I also know a low temp TXV is not adjusted to achieve 0F superheat at the outlet of the coil before the valve starts throttling closed.

You should re-read what I wrote. I wrote about -40’F, about being the operative word. I intentionally wrote about because the actual set value of the particular TXV's superheat is unknown.

What blows my mind here is how you've dismissed the possibility of mixed refrigerant in the system based on nothing more than wild assumptions...with virtually zero quantifiable data to back it up.

You know how a TXV works - and with this knowledge are able to definitively determine whether or not a system is contaminated with mixed refrigerant?

You misinterpreted what I wrote. I didn’t dismiss the possibility of there being refrigerant contamination. I clearly stated in a few posts back... “So we can rule out refrigerant contamination for now.”

If you re-read what I wrote, I was saying that contamination of the refrigerant would not likely be the cause of the particular problem. As in the particular problem that the OP posted about. You have misinterpreted what I have written as a general blanket statement regarding refrigerant contamination. That’s not the case at all and if I were to make such a ludicrous blanket statement then my mind would have to be equally blown too.

Let me make it a little clearer.

The OP stated that the system was running with a suction pressure of between 3 to 5psi. Frost only forming after the TXV to the evap. Discharge air temp from the FDC was about 10 to 15’F, which is not really a proper indication of the overall evaporator temperature but gives a rough indication. Also, the box temperature was abnormally warm, hence the reason why they were called out in the first place I imagine.

In order for the suction pressure to be so low there would be two likely possibilities, given the data, observations and actions taken by the OP. Either the temperature at the TXV sensor was cold enough to cause the TXV to throttle back so much or the TXV had issues and was starving the evaporator. Considering the box temperature was abnormally warm it is reasonable to presume that the evaporator temperature was likewise abnormally warm for the given suction pressure. Otherwise, it would have been doing a better job of cooling the box.

Now even if there were refrigerant contamination, the temperature at the TXV sensor would still need to be cold enough to make it throttle to cause a suction pressure of 3 to 5psi. In fact, it wouldn’t matter what refrigerant was in the system, the temperature at the sensor would still need to be corresponding cold for the TXV to throttle to cause such a low suction pressure. Otherwise, the TXV would have issues/be faulty.

That was my reasoning for measuring the temperature at the TXV sensor, to determine if the TXV was working correctly or not for the given suction pressure.

If it were me, I'd be checking my LL drier, TXV inlet screen, look into the possibility of a condenser flooding valve issue....and whatever else I could think of, before haphazardly horking around with the TXV adjustment stem just for drill.

The measurements and observations given by the OP didn’t point to there being irregularities with those. And as far as the TXV strainer, that is a part of the TXV and is why I said ‘TXV issues’.

I gave my systematic reasoning leading up to checking the TXV. I don’t haphazardly hork around and am not sure what I wrote to give you that impression.

Also, I didn’t second guess the abilities or aptitude of the OP in providing his observations and intentional omissions, even wrote “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.”

[malcor]

I agree. If there is an inclination, especially from the equipment owner, the charge is messed up, put new gas in it and remove the doubt from the equasion.

Here's the thing. In the restaurant business, most of your owners and managers who have been in the business for awhile, know what's involved in refrigeration repairs. This is why the tech not only needs to have a knowledge of his craft, but also of customer relations. The second I hear "Well, maybe this is wrong", I know someone else f'ed with it. They called me now because the guy who f'ed with it is no longer around for whatever reasons. Of course they want to save money and you will hear about it, over and over. If you fix it right they will call you back. To play guessing games with the customers money is setting yourself up to lose the customer. Be honest with them up front.

I agree with you.

I just said that if a customer told me that they thought that ‘such and such’ was wrong with their equipment that I would verify their claim.

Almost on a daily basis I get told what is wrong with a system on arrival to a job, ranging from kitchen staff to building engineers. I am used to sifting through the information and verifying any valid concerns. I just don’t outright take their word for it blindly. That would be irresponsible and unprofessional on my part, after all they are paying me to diagnose and repair their equipment. They don’t call me so they can tell me how to repair their equipment.

[malcor]

How would you say that R410a can fractionate with a 0.3 degree glide yet say that 404a cannot with a 1.1 degree glide?

Either refrigerant CAN fractionate, but it isn't likely for either to do so in actual use.

You misunderstood what I wrote.

I stated that if R404a were contaminated with R410a or R407c (or any other refrigerant) that it would be highly possible. That is because there would be a lot of uncertainty where blends were mixed, resulting in a new unknown refrigerant type. I never compared R410a to R404a and am not sure why you thought I did either.

[Bobbycold]

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...

With a screen name like NAVY06, I'm guessing he started working refrigeration the same place I started, the Navy and then the Coast Guard. They were funny about that stuff. It didn't take a lot for someone up the chain to decide that since there is a blended refrigerant that the next step (it may be the first step for a compressor has no power at contactor, if the Cheif Engineer was a fine arts major) is to reclaim the charge, weight the bottle and PT it to insure the blend is correct. Over time since retiring from the service, PTing the reclaimed gas is not my first step for troubleshooting, though in most cases I still reclaim critical charges that are low charge and refill by weight whenever the charge is suspected of being low. If NAVY06 stays at it, he will get past those extremely excessive, and unproductive things we all had to do in the service. Let me tell you a story from back when I was active duty. The Coast Guard had a Modspace trailer, and the authorized PM's included a weekly check of the suction pressure. It doesn't matter to the service that every time you put the gage set on it you take two 6 foot hoses of gas out of the system, someone had a bright idea, and I must obey. I requested the short hose and single suction gage, but it never appeared. After about a month and a half of faithfully preforming my duties, as you can guess, the suction pressure was below the very ridged standard set out in the same instruction that required gages on a perfectly fine operating unit. One unit had such a requirement for an ice machine, but after talking to the chief, it was felt that we could skip that. I have no doubt that NAVY06 probably did this awhile with the Navy, and will likely break the bad service methods as time continues.

There is reason to suspect that there may be a seperated blend, but I don't think it would be my next check. If the blend seperated, I doubt it was from use. Most likely the owner charged as a gas.

[markettech]

You should re-read what I wrote. I wrote about -40’F, about being the operative word. I intentionally wrote about because the actual set value of the particular TXV's superheat is unknown.





You misinterpreted what I wrote. I didn’t dismiss the possibility of there being refrigerant contamination. I clearly stated in a few posts back... “So we can rule out refrigerant contamination for now.”

If you re-read what I wrote, I was saying that contamination of the refrigerant would not likely be the cause of the particular problem. As in the particular problem that the OP posted about. You have misinterpreted what I have written as a general blanket statement regarding refrigerant contamination. That’s not the case at all and if I were to make such a ludicrous blanket statement then my mind would have to be equally blown too.

Let me make it a little clearer.

The OP stated that the system was running with a suction pressure of between 3 to 5psi. Frost only forming after the TXV to the evap. Discharge air temp from the FDC was about 10 to 15’F, which is not really a proper indication of the overall evaporator temperature but gives a rough indication. Also, the box temperature was abnormally warm, hence the reason why they were called out in the first place I imagine.

In order for the suction pressure to be so low there would be two likely possibilities, given the data, observations and actions taken by the OP. Either the temperature at the TXV sensor was cold enough to cause the TXV to throttle back so much or the TXV had issues and was starving the evaporator. Considering the box temperature was abnormally warm it is reasonable to presume that the evaporator temperature was likewise abnormally warm for the given suction pressure. Otherwise, it would have been doing a better job of cooling the box.

Now even if there were refrigerant contamination, the temperature at the TXV sensor would still need to be cold enough to make it throttle to cause a suction pressure of 3 to 5psi. In fact, it wouldn’t matter what refrigerant was in the system, the temperature at the sensor would still need to be corresponding cold for the TXV to throttle to cause such a low suction pressure. Otherwise, the TXV would have issues/be faulty.

That was my reasoning for measuring the temperature at the TXV sensor, to determine if the TXV was working correctly or not for the given suction pressure.





The measurements and observations given by the OP didn’t point to there being irregularities with those. And as far as the TXV strainer, that is a part of the TXV and is why I said ‘TXV issues’.

I gave my systematic reasoning leading up to checking the TXV. I don’t haphazardly hork around and am not sure what I wrote to give you that impression.

Also, I didn’t second guess the abilities or aptitude of the OP in providing his observations and intentional omissions, even wrote “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 honestly could care less why you purposely entered a certain word or made a specific statement.

That said, I am rather curious as to the purpose of your condescending attitude earlier in this thread...which was apparently directed at individuals who responded to the OP prior to you. Regardless of the reason, hopefully it fulfilled whatever emotional need you had at the time.

[malcor]

After noticing hostility towards me I started reading around the other topics here. I have come to realise that people who are learning the trade are encouraged to ‘get their post count up’ with posts that have technical content. Now that I realise that, I can see that my first post in this topic (#9) was uncalled for and out of line. It was a misunderstanding on my part and showed poor judgment.

It wasn’t my intention to offend anyone and I certainly didn’t want to discourage anyone from participating here, especially someone who is here specifically to increase their knowledge. I made a error in judgement and I apologise for any offence that I may have caused Navy06 and to anyone else that I may have offended too.

[malcor]

I honestly could care less why you purposely entered a certain word or made a specific statement.

That said, I am rather curious as to the purpose of your condescending attitude earlier in this thread...which was apparently directed at individuals who responded to the OP prior to you. Regardless of the reason, hopefully it fulfilled whatever emotional need you had at the time.

The problem with typing here on the forums is that you don’t get the visual and tonal cues that you get from a normal face to face conversation. I'm not a condescending person at all and I really meant no offence. Perhaps it’s my writing style or the way I expressed what I was trying to say, that gave that impression. I actually came to this web site with the mindset of having a technical rumble in the dirt with my peers. I didn’t come here to offend anyone or to make trouble. And that’s the truth.