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There are too many different opinions on proper charging methods for coolers and freezers. I have heard 20 degree superheat at the compressor, clear sight glass, I've even heard someone say you can go as low as 5 degree superheat at the compressor for freezers. I want to be the best Service tech I can be and do it the right way. Can some of you guys tell me the proper way to charge for both TXV and cap tube systems for freezers and coolers. I am very interested in learning correct way.
Our copeland rep demands 20 degrees at the compressor, no matter what the application. Be kind to your compressors.
Still, you come on a box thats run with 5 degrees and has been so for years - why change it? Personally, I shoot for
20 when I do adjust it.
Compressor superheat & liquid subcooling with clean coils will confirm a proper charge all day every day. Superheat is different with every compressor, although, in my opinion, if it's a txv system, you can run it down to 5F as long as the compressor sees 100% vapour, your laughung. Even if the slight chance of liquid at the compressor, it's so hot inside there, it'll boil off as soon as it passes the valve. Look for 10F to 20F subcooling.
You are talking about two differant things. On a txv system you Charge the system to a clear sight glass. When the sight glass is clear under the heavyest load there is enough refrigerant in there. The Superheat is the setting on the TXV and has nothing to do with the charge. If the compressor is real close to the coil, say a on top of the walk in or at the refrigerator, then yes I would say that 20 degrees of superheat at the compressor is a good spot. If the compressor is in the mechanical room 200 feet away from the refer case then 20 degrees means you are refrigerating the ground if the pipe is in the ground, or you are refrigerating the overhead space above the ceiling. Set the superheat at the fixture where the bulb for the TXV is located, not at some arbitrary point on the suction pipe.
If it is a cap tube system you need to have the fixture down to temp before you can chewck superheat at the outlet of the coil. This means adding refrigerant slowly and measureing the temp of the fixture and the superheat on the suction (usually where it exits the cabinet. If at all possible see if the unit tag specifies the charge weight, weigh the charge in and then you are set to go.
Copelands are rated to a suction gas temperature of 65 degrees. About the only application where this is high is for low temp R-22Quote:
Originally posted by gbfromsd
Our copeland rep demands 20 degrees at the compressor, no matter what the application. Be kind to your compressors.
Still, you come on a box thats run with 5 degrees and has been so for years - why change it? Personally, I shoot for
20 when I do adjust it.
Lets assume that all valves are ajusted at the fixture as referdude has correctly stated. We also assume the compressor(s) are functioning normally.
If this is the case, and you are having superheat problems at the compressor. Check the insulation on your lines.
Even though ther is alot of science to this job, it's an art to do this job.
You find that each service call may, at the surface, to be the same but its not. Almost as if if unit that you work on has its own personality. Wear and tear to the comperessor is different effecting its effiency. location in the unit is different, next to the grill, outside, it's all each different.
Ask yourself, "do I fell good about this charge?"
The anwser is with in yourself Grasshopper.
'The road to enlitenment is long and difficult,, make sure to have pluty of beer and porn for the trip.'
20 degrees at the compressor, that's all they ask.
I've talked to two different Copeland reps. They give training classes at our local distributors. The gist of the class on compressor failures is: It's not our compressors, it's your systems They analyze failures and
the vast majority fail from floodback, burnout - you know the story.
Although you might look for 5 degrees of S/H at the TXV bulb, Copeland wants 20 at the compressor suction. In
practice - I find this to be satisfactory.