best way to check superheat

[pelican]

super heat is only posible when there is no liguid present other wise you have a saturated gas ie liquid and vapor present which would be the temperature on your p/t chart.so the liquid has to be boiled off before the vapor can be super heated.hope this helps.

[jpsmith1cm]

Most compressors are not capable of pumping liquid is doesn't compress it hydraulics in the pump and destroyes the pump.
Hermetic compressors are cooled by suction gas.

BINGO! There should NEVER be liquid refrigerant in the compressor. If there is, you have a major problem. Even less so an air cooled compressor. The refrigerant gas runs directly into the cylinder rather than passing over the windings first. A refrigerant cooled compressor can forgive an occasional dribble of liquid back the suction line, an air cooled will make quick scrap if you allow liquid in.

If you have even 1 degree of superheat, by definition, you cannot have liquid present in the line. I have gotten into heated debates with people over this, usually people who didn't study hard enough in tech school. Several seasoned techs that work for my company believe that there should not be ice on suction lines, EVEN ON FROZEN FOOD!!! I have talked myself blue in the face trying to explain that to manage that on a -23F rack, keeping the lines ice free requires 55 degrees of superheat to the compressor. Do the math. You can have lines at -3 degrees and still have 20 degrees superheat at the compressor which is the manufacturer's recommended minimum superheat. If you've got a -3 degree line, you WILL have ice buildup on that line.

That is where your compressor cooling comes from, not liquid, but superheated vapor that is still cooler than the motor windings.

[BamaCool]

Yes that is correct even though the compressor is air cooled the the compressor still needs a small amount of liquid coming back to cool the windings. Someone please correct me if you feel im wrong....

I was going to, everybody else beat me to it! Suction line+liquid=forked compressor! Even though scrolls can handle some, not a good thing to have!

[stanbyyourword]

schreader core remover tool with inline thermometer " kit ", as accurate as you will ever get regards stan

[beachtech]

The compressor needs that liquid to keep it cool.

maybe we should start at, what is the definition of superheat?

anyone here wanna take a stab at it?

i am pretty sure the word liquid is nowhere in that def.

[beachtech]

schreader core remover tool with inline thermometer " kit ", as accurate as you will ever get regards stan

yellow jacket makes the kit i have

[btcstudenthvacr]

maybe we should start at, what is the definition of superheat?

anyone here wanna take a stab at it?


i am pretty sure the word liquid is nowhere in that def.

Superheat is the sensible heat added to the refrigerant vapor after the change of state has take place. Off the top of my head. Had a test of evaporators today got an A...Half was hands on and half was mental and paper...

[stomper56]

Well to have superheat by definition you cant have liquid only superheated vapor.
If there was no superheat then there is liquid ie in the saturated state and you will have what i like to call a "DCP" dead compressor pumping because its only a matter of time
Its the superheated vapor that cools the motor windings and removes the heat of compression at the same time.

[btcstudenthvacr]

Well to have superheat by definition you cant have liquid only superheated vapor.
If there was no superheat then there is liquid ie in the saturated state and you will have what i like to call a "DCP" dead compressor pumping because its only a matter of time
Its the superheated vapor that cools the motor windings and removes the heat of compression at the same time.

What I already said

[stomper56]

What I already said

So whats your point, this isn't a competition i posted it for others so they might understand it better

[RAbubaker]

Here is the key factor that most of us out in the field take superheat, which is to verify the charge on a system. Especially on a older system that may have lost some of it's capacity. Taking your temp reading at the evaporator on the suction line & the other is 6" to 8" from the compressor. I have tried both & have not gotten good readings, even on a new system. Have any of you had better lucky? If you have, then where did you take your temp at?