lennyb,
From reading your last couple of posts, I think that you are having some difficulty understanding superheat.
On the low temp stuff that I work on, a suction line of -10 to -15 at the evaporator isn't abnormal at all.
Any freezer at -10 no matter which refrigerant is gonna have a vapor line temp at the TXV bulb of 10° or less. Other wise the freezer wouldn't be able to be at -10.
lennyb,
From reading your last couple of posts, I think that you are having some difficulty understanding superheat.
On the low temp stuff that I work on, a suction line of -10 to -15 at the evaporator isn't abnormal at all.
Evap is Baily M# BF200B-1
TXV is a SBF5E-A-Z
Compressor is a Copland
EAVA1-021E-TAC-800
208V 3HP. 60HZ
I opened up TXV and SH is jumping around at 10 to 30, noticed right side fan is only running about 1/2 speed.
Plan is to change Fan motor then watch and adjust SH, if its still jumping around I will change TXV
Changed both fan motors and returned TXV back to center, de-iced both side of evap coil. Box got down to 16 Deg. and SH was still 50 Deg.
My question is that I'm going by simple math equations. when my gauge temp says a neg temp it gets added to the suction line temp not subtracted correct?
Another question.
When working with refridgerants that im not used to working with how do I determine what is or would be a good running Temp/PSIG for the application.
Such as
409a Freezer
414b Freezer
414b cooler
404a Freezer
404a cooler
Don't think about the pressure so much. Its always the saturation temp that counts.
Weather 404a, 409a, or 414b, a -10 freezer means you'll have a saturation temp of minus 20 or lower when the freezer is at or near -10.
Get some P/T charts.
And in your post, you said you have a 16* box. since your suction line temperature at the coil isn't going to be above your box temperature. And you said you have 50* superheat, at best you have a Suction line temp at 16* and a SST of -34* for 50* superheat.
If the valve is frosting over its restricted. Clean the strainer if it has one, or replace the valve. Some valves can be torn apart and cleaned, I prefer to replace them. You want to see 6-10 deg superheat at the bulb as someone already posted.
I disagree about just looking at the valve being iced over indicating a problem. If the line temperature is below freezing, what's going to happen? Even with a properly operating valve??
The poster stated the evap was iced. After he thawed the ice, the suction pressure & box temp are dropping as they should but his discharge is still hanging tight at 175. He needs to properly charge the unit, and now that he has adj the txv, he may need to re-adj the SH once box temps are near spec. In addition, he needs to test and confirm his defrost cycle is set and working correctly or possibly an abundance of humid air leaking into the box due to either improper use, no door strips, etc. And I am assuming he knows how to take an accurate temp reading at the outlet of the evap under the conditions.
Just curious this is kinda on topic. when you are doing calculations on walk-in coolers/freezers i usually get my Sh by the inlet of the compressor would that be good place to grab it or is it always "better" to grab it at a few inches downstream from the evap a little bit past the bulb.
The reason i do it at the compressor is because its a lot easier and i dont have to take off the cover for it its right at the valves. Just wanting your opinion? thx
(total superheat compared to superheat of the evaporator only)
Last edited by akelesis; 08-20-2012 at 06:55 AM. Reason: re-worded some things (-:
Get er Done!
Do what has to be done
when it has to be done
as well as it has to be done
And doing it all the time.