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I have mostly been working on residential air conditioning. Due to a shortage of techs here in my town I have found myself making the transition into walk-in refrigerators and freezers. I am not really too concerned about the electrical as I am the refrigerant charging.
I know superheat and subcooling. Do most of these walk-ins come with TXV's? If so, will I use 10 - 15 degree subcooling on walk-ins as I have in the past with comfort cooling?
Will I be using superheat? What are the biggest differences from walk-ins and comfort cooling with regard to refrigerant charging?
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All walk-in system use TEVs for refrigerant metering with the exception of some proprietary systems like Heatcraft's Beacon system that use electric expansion valves. They also generally have receivers except for Russell's High Sierra system.
The basic difference between walk-ins and typical split A/C systems then is that A/C systems are critically charged whereas refrigeration systems are not. For that reason they are not charged in the same manner.
You already know that on an A/C system with a cap tube you're essentially charging by suction superheat and on a system with a TEV by liquid subcooling. This is done because the amount of refrigerant in the system will cause these values to change. When you hit your mark, you're done.
On a refrigeration system you basically charge to a full column of liquid by clearing the sightglass. If the system includes some form of condenser flooding control like a Headmaster, you must then add more refrigerant to account for the amount of refrigerant that gets stacked up in the condenser in cold weather.
It's always best to follow the manufacturers' recommendations when installing any system. Heatcraft has what is probably the best manual out there for commercial walk-ins. Read it, study it and understand it. You'll be far ahead of those who don't.
Heatcraft Installation and Operating Manual
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dear, ice meister,not too break your bubble but i think you are miss informed,refrigeration systems are also critically charged as well,as for a/c systems, have have yet to see one with a cap tube.could be wrong mind you, butttttttttttttttt.
if at first you dont succeed,then skydiving is not for you
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Just changed a 2 horse cast iron body on a walk in cooler,3 phase,changed out filter dryer,contactor,fixed freon leaks,new condensor fan moter,added 1 oz.of acid away just incase,system didnt seem to be cooling that well,pressures was 18 and 175,so i came back about 4 hrs later and checked walkin temp it was at 40,so i played with charge somewhat,took superheat after adding a little 409 and suction stayed about 18 and line temp was around 34,16 degree superheat then i checked subcooling,pressure at 185 and line temp at 110.Had about 22 degree of subcooling,so letting it sit over night to see how it looks in the morning,ya i think the charge is somewhat pretty critical in refrigeration but hard to go from one to another.
There are three signs of old age.
The first is your loss of memory,
the other two I forget.
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critical - a minor difference in charge volume has a major impact on performance.
I haven't seen a TXV/RCVR/Sg unit that required a critical charge yet. I have seen small appliance size restaurant equipment that did require a critical charge, but it had a cap tube.
You can overcharge a TXV and it'll be just fine as long as the head pressure remains nearly constant. Thus it is not a critical charge.
The basic concepts of charge apply in the same manner and to the same degree regardless of application. Gas is gas man.
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Originally posted by len
dear, ice meister,not too break your bubble but i think you are miss informed,refrigeration systems are also critically charged as well,as for a/c systems, have have yet to see one with a cap tube.could be wrong mind you, butttttttttttttttt.
Len.....The subject concerned the difference between A/C and walk-in system charging. I didn't want to confuse the issue with self-contained wannabe refrigeration systems like those in True and Beverage Air reach-ins.
As for A/C system and cap tubes, I should have said fixed metering type systems instead of cap tubes.....it would have been clearer and a little more up-to-date. Many split A/C systems had capillary tube feeds before most manufacturers switched over to flow check pistons type feed.
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Originally posted by hillbilly tech
Just changed a 2 horse cast iron body on a walk in cooler,3 phase,changed out filter dryer,contactor,fixed freon leaks,new condensor fan moter,added 1 oz.of acid away just incase,system didnt seem to be cooling that well,pressures was 18 and 175,so i came back about 4 hrs later and checked walkin temp it was at 40,so i played with charge somewhat,took superheat after adding a little 409 and suction stayed about 18 and line temp was around 34,16 degree superheat then i checked subcooling,pressure at 185 and line temp at 110.Had about 22 degree of subcooling,so letting it sit over night to see how it looks in the morning,ya i think the charge is somewhat pretty critical in refrigeration but hard to go from one to another.
Hill, did you liquid charged it? at 18psi suction the evaporator should be near 20 degrees.
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i stand to be corrected
if at first you dont succeed,then skydiving is not for you
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Hvacpope,ya i liquid charged it on the high side,vacumm sucked most of the freon in,added a little later on the low side,i know its a no no but what else do ya do,anyway box is running good and cold now,but i will be keepen a eye on it,pass by there everyday.
There are three signs of old age.
The first is your loss of memory,
the other two I forget.
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well.
let me see here.
40 degree coil with a 15 degree TD is 55 degree discharge air, at design load. sounds like refrigeration to me.
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Ice, you said it is charged to a full column of liquid by clearing the sightglass. I have never charged to a sightglass and am sure it is not difficult. I just need a little guidance. Do I just add refrigerant till I start to see the liquid in the sightglass? Where do I stop charging, when liquid is present at the bottom, center, or all the way at the top of the sightglass?
Also, if I wanted to charge by superheat would that be acceptable also? If so, is between 20 - 30 degrees a correct superheat?
Would I completely leave out subcooling?
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The biggest difference with a txv system I see would be the presence of a receiver to store excess liquid. Superheat is set at the evaporator outlet, not the compressor. The goal is a clear glass, plus the needs of any low ambient device.
Superheat in boxes, cooler 8-12 degrees freezer 4-6 degrees.
I feel installing any walk-in without a in line heat exchanger is foolish.
This will flash any returning liquid in the suction line and sub cool and insure a full Colum of liquid at the txv.
A Diamond is just a piece of coal, that made good under pressure!
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Do not charge by sub-cooling. Add refrigerant until you can see it flowing through the sight glass. Keep adding refrigerant until the sight glass clears. Let the system run for a few minutes to make sure the sight glass stays clear. Add more if necessary. At this point add flooding charge if you have a flooding control valve.
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a little help on determining the flood charge that should be added after a full sight glass on systems with a headmaster control would be greatly appreciated.Also wouldn't adding more charge change my sub-cooling? Is 15-20 F about normal sub-cool for a txv?
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http://www.sporlan.com/90-30-1.pdf
Or just charge it on the coldest day of the year.
[Edited by stat on 06-23-2006 at 12:06 AM]
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I've often thought about adding the above statement to 90-30-1.
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In any case, if they don't gas it to specs, they are sure to be there on the coldest day of the year.
A Diamond is just a piece of coal, that made good under pressure!
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They only refrigerant you can clear a sight glass on are R22, r12, 502.
12, 502 are out dated and very seldom you find r22 in a walkin, you do see them but not often
All blends should never have a clear sight glass, you charge 80 to 85 % of your existing charge when converting to a blend.
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Originally posted by t&mechanical
They only refrigerant you can clear a sight glass on are R22, r12, 502.
12, 502 are out dated and very seldom you find r22 in a walkin, you do see them but not often
All blends should never have a clear sight glass, you charge 80 to 85 % of your existing charge when converting to a blend.
FALSE!!!!! If you have a receiver, full column of juice.
On critically charged units with s/g's you will see bubbles.