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02-12-2012, 08:54 PM #1
Mixing Refrigerant on a Rack a problem?...How say you?
Alright, last week I was working on this Rack. The engineering chart mounted on the wall said it was a R-402A (HP80) suction group. However the Rack itself was labeled in several locations that it had R-408A dated as far back as 2009. The Rack design is a +15*SST per the engineering chart.
The EMS programming was setup to run as a +15*SST R-408A, which is a 44# set point.
The problem was called in as, multiple cases are freezing product. This Rack at one time was setup to float suction pressure set point...but overtime has been been disabled by circuits being setback up into EMS Full control, EPR's being stemmed back into control and T-stats being setback into control range.
After spending some time setting those temperature controls back below range and letting the case temperatures be controlled by Rack suction pressure, re-enabling floating suction set point and controlling it with my meat cases discharge air sensors. I had every case on that suction group running too cold and freezing product in short order
My suction set point had floated up 10# which made it a 54# set point or 24*SST R-408A
My Float circuit set point was 29*, and even running at max float set point 54#, my cases were running actual discharge air at 25*-26*....Now I either have the most efficient cases on the planet that can maintain a 1*-2* TD or something is not right.
I go down to the cases and start checking superheat using my R-408A PT chart and start reading superheat values that are in the negative 2*-4* range...now I know open air cases do not run 1* TD's and negative superheat values are impossible. I've come to the conclusion that whoever labeled the Rack as R-408A in 2009 was an idiot.
Go back to the machine room, re-adjust all suction group parameters to run on R-402A set points.
+15*SST 53# with a max float 63#.
Now everything starts jiving like is supposed to do. Cases are running 8*-10* TD's, superheat values are positive and the rack starts purring along, you can actually hear it run smoother.
Attached is graphs of the suction pressure and some case temperatures. Notice how much tighter the suction pressure and case temperature control is while operating under a properly operating floating suction.
But on to the original title of the post...MIXING REFRIGERANT...when does it become a problem? This rack above has a 800# Total Charge. This year it has already had 400# R-408A dumped into it due to leaks. However, the PT relationship is obviously dominate with R-402A. There are also R-507 racks out there that I know of when a guy dumped in 200# R-22 as a "tracer" that do not have any issues...maybe it matters on the smaller stuff, but when hundereds of pounds are involved. I know it's not good to do, but I call BS on it being that big of an issue. And I base this on experience...whats your experiences/opinions?
02-13-2012, 12:17 AM #2
I see where you are coming from.
First, Had an old Hussman Koolgas that was running 402a, and was low. The tech had about 150lbs of 408 on his truck and dumped it in 'to get it running'. Next day, leak was fixed, topped off with 402a, and never had a problem.
Had one a while back, the store had both 407 and 507 racks, and the drum color is similar.. and of course both are *07. 507 was accidentally put in the 407 rack, maybe 100lbs in an 800-1000 lb rack, never caused a problem.
On the 402/408 one, the main component is 22, so you technically would only be mixing whatever the other components are. Doesn't 402/408 separate components when leaking? One component leaks first?
Anyway, to the point of my reply, I've never seen it cause a problem, I guess it wouldn't until the 'wrong' refrigerant became the dominant one, but at what level would that happen?
Maybe that is a new way to do conversions.. just top off with the new gas and eventually through leaks, etc.. it will be converted. Lame, I know.There's no such thing as normal,Just different kinds of crazy..
02-13-2012, 07:51 AM #3
Seen a guy one time ... cough ... top off a Hp80 rack with some R22 during an emergency call , had leak in the sight glass. This was 2 years ago and still going strong
02-13-2012, 11:55 PM #4
I'm sure if you've been doing this a while, you've seen it or done it yourself. I have erred several time. Worst was adding 300# of 507 to a MT 134a rack that held 5-600#. I don't know of long term issues, but for the remainder of the contract, it did fine. I've added 404 to 507 racks and vice versa, whatever. Mistakes were bound to happen as much as we were working during the retrofit days. Just a couple months ago, 200# of 404 was added to an R-22 LT rack holding 1200# because they were next to it. It already has POE, so we'll see what happens.
The most negative things I've seen is from:
Introduction of three 60 bottles of nitrogen into an already charged Protocol. The plate condenser wasn't doing squat.
Water being intentionally injected into a system. That guy was always plotting something.
Don't get me wrong, there are instances just completely goofed and charged the wrong type of gas from EMPTY, of course that'll show up quick.
Or like in the OP's example, the rack gets labeled from a GUESS and it continues from there.
02-14-2012, 06:34 PM #5
You asked "how say you" and I say don't do it! That being said I remember an incident about 12 years ago where I did it with major consequences.
It was not a Rack but a pretty big single something like 72' of dairy cases. It was an R-12 that was converted to MP-39. I didnt have enough gas on the truck to fill it so I was robbing gas out another system and hooked up to the wrong liquid line...ops!!
Head pressure went ski hi and it didnt work at all. Had to dump the entire charge and start over. Ever since then I have been very careful to make sure I'm charging with the correct R.
I have seen an old co-worker put 60lbs of 22 in a 402 rack with no ill results. So short story long I have no clue lol. I just try not to do it.
02-14-2012, 06:58 PM #6
I don't know that I've ever mixed refrigerants.
Not in any serious amount, anyway. A little bit from my hoses doesn't count on a system holding 1000#....
I've seen a couple of systems with mixed or wrong gas in them.
High head was the most common symptom.
02-14-2012, 10:53 PM #7
I don't believe I've ever added the wrong refrigerant. (at least on purpose)
And I know I've worked on a slew of equipment that is mixed with no ill results.
The only times I've seen issues is with air or nitrogen in the system.
for the most part, I guess when you start having gasses that just don't act like refrigerant is when the problems occur.
02-15-2012, 10:07 PM #8
I've never seen it be a problem
I think the only time you'll have an issue is if you have to be somewhere else and or it's Friday night
I'd be curious if you recovered some into a tank and did the PT test after a day of EQ time to see how close to what gas you have.
That graph should be the proof for all the "float haters"
02-15-2012, 10:22 PM #9
02-16-2012, 09:00 AM #10
R-404A: R-125 (44%), R-143A (52%). R-134A (4%)
R-507: R-125 (50%), R-143A (50%)
Genetron, who developed R-507, used to say that you could mix R-404A and R-507 without any problems. They are close in their chemical makeup.
Of course, DuPont had the lion's share of the market compared to R-507, and they never endorsed this.
02-16-2012, 10:22 PM #11
02-17-2012, 10:02 AM #12
It's not so much about whether blending refrigerants will allow a system to work adequately (although blending refrigerants that chemically have little in common with each other can have detrimental results).
It's more about not having any definitive pressure/temperature relationship that you can use to set anything that requires a precise pressure setting.
02-17-2012, 04:23 PM #13Regular Guest
- Join Date
- Feb 2012
Mixing refrigerants is never a good practice, but it some times happens.
That being said, checking the txv's on evap. coils connected to the rack in question is a way that I have determined the refrigerant in the system when the rack labeling is in question. My concern for mixing gas is not so much product integrity/case teperatures, or suction pressures as graphed above through the Einstien controller because the alarm perameters tripping will let you know real quick if temps are out of line too much,,not to mention that pesky market manager breathing down your neck about decreased shelf life of his product.
My concern is increased compression ratios, increased runtime on the compressors due to possible decreased BTU's per pound pumped of the new refrigerant feild blended, and long term system damage.
Something else to confirm besides the temps and pressures, gas defrost must have adiquate heat to defrost the coils by the end of the failsafe time limits set in the defrost perameters.. Nothing worse than washing all the cases out on a rack. Additional, as we all should know, what works in the winter or mild temps may not hold true in the summer months..
My recommendation is to go back and correct the issue when the opportunity comes available.
More food for thought, many times remodels in stores take place by department, so some of the medium temp cases on the rack may be more efficient than the older cases, so unless you look at all the system temperatures you dont really know that its all "OK".