target superheat

[mark beiser]

If the unit has a charging chart I use it.

Unless it is a Rheem/Ruud system, and the indoor temp isn't near the normal "comfort" level, or near 50% RH.

[beenthere]

You use the return WB for determining SH.
Don't take return and supply and mix them together.

[aintitfun]

You use the return WB for determining SH.
Don't take return and supply and mix them together.

I have been using return wb only, I know others that do the "mix", which I didnt think was right, thanks for the reply.

[emcoasthvacr]

Most of the TXV systems use subcooling.

With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.

[aintitfun]

Most of the TXV systems use subcooling.

With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.

The charts only provide the pressure and temp at a glance, they do not explain anything about the operation, I didnt see you mention anything about wet bulb temp,

[mknox]

i realize that if there is a chart in/on the odu its best to use it; but i see alot of units with only subcooling charts on them. if its got a txv, no good. our company will work on anything so i dont have charts from every manufacturer. i ve found a good deal of difference between manufacturers, unit size, and especially freon type. i guess what im really looking for is how everyone feels about the formula i posted originally{ wb x 3 - oat divided by 2 = target superheat }. is it universal?, does it work for all refrigerants? all replies welcome.

[beenthere]

It will work on any fixed metering device A/C.

[mikelcs]

Most of the TXV systems use subcooling.

With fixed bore metering, your superheat will usually be between 10 & 20 -- decreasing with higher ambient.

Amatures use charts -- if your a skilled tech, you shouldn't need a chart.

I'm an engineer & tech and do 5 to 10 calls a day and never needed a chart -- you either understand air conditioning, or you don't.

say what!! If you understand A/C- you should know that readings and formulas are critical. I have been blessed over the years to work with some of the best in this business. They understand air conditioning- and they all use charts and meters. Anyone who thinks that they know enough to get by with the hail mary method is not helping anyone out. Return air wet bulb will not only help you calculate target superheat, but proper airflow as well- IF YOU USE THE CHART!

[aintitfun]

i realize that if there is a chart in/on the odu its best to use it; but i see alot of units with only subcooling charts on them. if its got a txv, no good. our company will work on anything so i dont have charts from every manufacturer. i ve found a good deal of difference between manufacturers, unit size, and especially freon type. i guess what im really looking for is how everyone feels about the formula i posted originally{ wb x 3 - oat divided by 2 = target superheat }. is it universal?, does it work for all refrigerants? all replies welcome.

The differences you are seeing are between manufacturers, and SEER ratings in the case of Subcooling. R22 and R410A , you are not going to have different requirements just because of the refrigerant used, you may because of equipment efficiency. But that formula works for both refrigerants, difference is, you will probably not see too many 410A systems without a TXV, so you will most likely be using subcooling.

[mikelcs]

so ive seen a number of target superheat charts around but am wondering a calculation ive recently stumbled upon. wet bulb times 3,minus 80, minus outdoor ambient temp.. just wondering if most use a standard chart, try and go by what is on/in the odu, or mabey this calculation? any input is welcome...

eg. 100* O.A.T., 68*wb R.A.T
68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
same conditions w/ the chart I use says target is 12*
What does everyone else's chart say?

[beenthere]

eg. 100* O.A.T., 68*wb R.A.T
68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
same conditions w/ the chart I use says target is 12*
What does everyone else's chart say?

You did it wrong.

68*3=204,-80=124,-100=24,/2=12

Target SH is 12°F.

[aintitfun]

eg. 100* O.A.T., 68*wb R.A.T
68x3= 204 - 80= 124 - 100* OAT= 24* superheat.
same conditions w/ the chart I use says target is 12*
What does everyone else's chart say?

You forgot to divide by 2, your target sh is 12

[mikelcs]

i didn't see the /2 on the original post- i got that now