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Thread: frost top construction ???
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28-06-2003, 10:00 AM #151
Additional information:
My current job at this company is Systems / Oprerations Manager.
I am responsible for the computers, software & hardware, the operating systems for the company, inventory, the production workers (40), electrical trouble shooter, and blablabla. My degree is is Business Administration. You are prob. wondering - Why the @&*% are you working on something you don't know the first thing about??? We have gone thru three(3) Ref. Companies plus the original designers. There was no one left! I worked with the last guy for 2 days in Feb. on another unit - I saw a lot of guessing on his part - things you do not do in electrical / electronic trouble shooting, and we were paying $100.00 per hour.
So you see, this forum has been a tremendous help to me. You have cleared up so many issues.
Thank all who have participated so very much,
Tom
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28-06-2003, 07:10 PM #152
Tom
What refrigerant are you using R404a??
20 psig OUTLET pressure on the evaporator would be a saturation pressure of about -26.4 deg C (about -15 deg F) if your temperature at outlet is -4 deg F your superheat is about 11 deg F, or near enough to start with.
Regards. Andy
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28-06-2003, 10:18 PM #153
Tom Richardson,
In re: to superheat, read this:
http://www.hvacwebtech.com/trouble.htm
or this:
http://www.refimax.com/docs/therm_exp_valve.htm
Measure your suction line temperature exiting the evaporator (or cold plate).
Measure your suction pressure.
Refer to the "satuaration" temperature of your pressure reading on your pressure/temperature chart.
Subtract your saturation temperature of the refrigerant pressure (chart temperature reading) from your suction line temperature and the result is the superheat (the degrees above the boiling point that the refrigerant is at as it leaves the heat exchange device, evaporator or cold plate).
For medium temp, typically you want to be at about 7-9degrees, but in your close-coupled system a little bit more is not bad. You can adjust the responsiveness of your cold control scenario by relocated the cold control sensing location. For more positive reaction (defrost) you would locate the sensing location closer to the inlet of the evaporator.Last edited by herefishy; 28-06-2003 at 10:20 PM.
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28-06-2003, 10:24 PM #154Originally posted by Tom Richardson
*With the temps I am trying for, is R404a the correct refrigerant??
I.E., don't waste your time thinking about it. Actually, medium temp R-404A applications are becoming more common.
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29-06-2003, 08:48 PM #155
Tom, you need to go to my website and purchase the "TECH Method Lesson Series: ACR Trouble Shooting". It will help you a lot, although you also need hands on experience to go with it.
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29-06-2003, 09:01 PM #156Keep in mind EPR is set to 60psi which converts to ~25° F for evap coil. Can not acheive 24° setting, 25° is tough. Can I?
If you find that the new control settings DO NOT get you where you want to go, I am going to tell you to move the EPR to the common suction line and adjust it to control the frost top temperature.
If you find that the new control settings DO get you where you want to go, I am going to tell you to move the EPR to the common suction line and adjust it to control the frost top temperature.
And either way, I will keep telling you to adjust the TXV superheat.Last edited by Gary; 29-06-2003 at 09:24 PM.
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29-06-2003, 09:19 PM #157
If you want to do the whole thing in steps, here is the first step:
1. Move the EPR to the common suction line and adjust it to control the frost top temperature.
2. Adjust the TXV superheat.
3. Adjust the cold control.
4. After each step, give us a full set of pressure and temperature measurements all over the system, so we can see what it is doing. We can't see the system from here. We can only see your description of it and the temperature measurements you report to us.
You are trying to do step number 3 before you do steps 1 and 2. That is not the right way to do things. The sequence is important.Last edited by Gary; 29-06-2003 at 09:27 PM.
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29-06-2003, 11:19 PM #158
This certainly is not the first one of this type of box to be introduced. I've worked on this design from at least three other manufacturers.
All that I have seen thus far have the EPR controlling the fan coil, while letting the ice rail run wild.
It's the crappiest way to refrigerate that I have seen yet.
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30-06-2003, 10:55 AM #159
Mr Condenseddave,
Where have you seen a unit like I have described?
Who makes it?
What is a better way?
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Mr Gary,
You say move the EPR to a 'common line' with both evap & frost top, same line ??
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Sunday, The unit ran very well with temp setting of 26°F. and 34°F. for the air out temp. The frost top temp floated about 6°F., but this was not a problem, the media being tested kept at a controlled 33° to 36°. No Ice accumulated on evap coil!!!
The air out measurement is for reference, this is how 'they have always' measured the performance of an air over model.
Thanks guys,
Tom
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30-06-2003, 11:07 AM #160You say move the EPR to a 'common line' with both evap & frost top, same line ??
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30-06-2003, 11:44 AM #161
Gary,
What psi setting on EPR ??
Can EPR physically be located @ the compressor area???
What will take place when the evap cycles off??
Tom
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30-06-2003, 11:59 AM #162What psi setting on EPR ??
Can EPR physically be located @ the compressor area???
What will take place when the evap cycles off??Last edited by Gary; 30-06-2003 at 12:13 PM.
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30-06-2003, 07:06 PM #163
Hi Gary,
I'm am trying not to confuse the issue as much as possible (so I'm trying to keep my mouth shut when someone hits a good point, and something is being accomplished )
But, I might make the observation, that I believe that Tom Richardson stated that he was looking for a 30F cold plate temp.
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30-06-2003, 07:57 PM #164
I know just what you mean, Herefishy. It would be very easy to jump ahead and throw in a lot of things that we can see coming. But Tom is new to this and we need to do it a step at a time, in a logical sequence.
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01-07-2003, 12:14 AM #165
Note: In order to work correctly, we have to hold the frost top to 20°F. to 25°F., mistake on my part.
NEW BUG:
Changed the EPR to common suction. Everything worked fine for 3 hours, held temps, everything 'appeared' fine.
Then we opened the unit to check for ice. one of the 4 fans had quit working - there was ICE. We repaired the fan & decided to turn the fan speed up to 70% to defrost the coil faster. Wo and behold, I could never get the suction pressure below 65psi, and the frost top begain thawing. Turned the fans back to their 60% and the pressure started comming down! WHAT HAPPENDED??
WHAT TO DO NOW?
HELP!
TomLast edited by Tom Richardson; 01-07-2003 at 12:27 AM.
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01-07-2003, 03:10 AM #166
Leave the fans at 60%.
Does the frost top temperature get to where you want it now?
What was the EPR setting when everything was working fine and the frost top temperature was where you wanted it?Last edited by Gary; 01-07-2003 at 03:14 AM.
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01-07-2003, 06:24 AM #167Originally posted by Tom Richardson
Mr Condenseddave,
Where have you seen a unit like I have described?
Who makes it?
What is a better way?
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I may be wrong, but I believe Hussmann made these for a period, also, possibly in Brantford or Gloversville? Dan?
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01-07-2003, 06:32 AM #168
What are the following?
Evap air in:
Evap air out:
Pressure:
Suction line temp @ coil outlet (near TXV bulb):
Frost top temp:
Pressure:
Suction line temp @ coil outlet (near TXV bulb):
Low side pressure @ compressor:
Suction line temp @ compressor:
Cond air in temp:
Cond air out temp:
High side pressure:
Liquid line temp @ cond outlet:
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01-07-2003, 06:32 AM #169
Oh, yeah, no "Mr.", just Dave is fine. I'm not even related to anyone living who is a "Mr."
I'll call a friend int he morning who still services wawa to see if he can remember the mfg, or look at one in the next few days.
They're using 22, with an EPR on the blower coil, and a pressure control to cycle the compressor. The "Ice Rail", as I've always been led to call them, run in the neighborhood of +10 degrees F.
The name "Bloomington" rings a bell.
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01-07-2003, 02:52 PM #170
Tom Richardson, I am interested in the superheat conditions relating to the coil icing. Instead of using temperature/pressure superhaet reading method, apply a temp sensor at the TEV outlet, and another at the evap coil outlet (line temp before and after evaporator coil). What is the difference in temperature in and out.
If your icing condition is not smooth and even (like you would want to skat on it), you are not properly feeding your coil.
Do you still have the cold control at the improper cut-in setting of 34F ?
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01-07-2003, 03:50 PM #171
Now that the EPR is in the common suction line and controlling the frost top temperature, there should be a lot less confusion. Being controlled by the EPR, the frost top is no longer a problem area, we know exactly what the low end SST is for both coils, and the EPR compensates for the oversized compressor so we can set that issue aside for the moment.
We can now focus on the air coil without all of the side issues to confuse things.
As soon as we get a full set of pressure and temperature readings from Tom, we will know exactly where we stand and what we need to do next.Last edited by Gary; 01-07-2003 at 03:58 PM.
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12-07-2003, 01:32 AM #172
Gee willickers....
We haven't heard from Tom Richardson in awhile...
Did we scare him off ?
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12-07-2003, 01:59 AM #173
Good question. I sent him an e-mail a few weeks ago offering to stop by and take a look at his prototype because I was scheduled to be in town this week. He never replied. Maybe his bosses didn't like the idea. The offer is still open, Tom. Apparently I am permitted to remain at home for another week.
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18-08-2003, 09:26 AM #174
Apparently Mr. Richardson either figured it all out or gave up on us.
It's a shame. We were just starting to get somewhere. With the EPR controlling the frost top, we could tell what SST is needed. With the fan speed control at 60%, we can see that the evaporator is oversized. Once we get that sorted out, we can tell by the pressure entering the compressor exactly what size compressor is needed.Last edited by Gary; 18-08-2003 at 11:16 AM.
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18-08-2003, 04:12 PM #175
Maybe they didn't realize that this had been done already.
He seemed sort of surprised that this was not an original idea...
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