subcooling and supaheat calculations??

[kayl]

i always forget which way around things are, so i though i would get a thread started. This way I can book mark it
is this correct.

subcooling.
we take the pressure measurement at the condenser and convert that to degrees F.
we then measure the temperature of the liquid line after the condenser again in degrees F
subcooling an example now; example (r290) 150PSIG(89F) - 82F gives 7F (what is the ideal subcooling value?)


then i would do the same for supa heat. take the pressure and convert that to degrees F with table.

is it the difference between the pressure/temperature valve and the evap temperature (or is it the) temperature 6" from the compressor. (i always get messed up with this bit)
8F-12F is a good level of supaheat correct.

the negatives seem to stuff the answer up though.
Example: r290 at 10Hg and evap -50c and 6”from compressor is -40c.
10Hg(-60F) - -41F= -20F ??

and another system example: evap is -31c, 6”from the compressor is -20c, pressure 0spig
calculation
0psig(-43F) - -5F= -38F

or if I do it on the evap temperature.
0psig(-43F) - -25F= -18F

i remember that garry (what has happened to him, hasn’t been here for months) use to teach alot about this, he said it wasn’t about the temps its about getting these figures correct to enable the phase change system to function correctly and per long compressor life etc.
so any help i would appreciate