Quote Originally Posted by jmully View Post
this has been a big help, is it possible to measure evap superheat where there is no shrader valve on the suction line and the expansion valve equalizing line has been brazed in place? any help will be appreciated



No. Not with any accuracy because you cannot access to measure what you want to measure.

You may take the surface temperature of the pipe at the exit point of the evaporator, then measure the suction pressure at the compressor service valve if this is available to you, adjusting the pressure reading for your estimated pressure loss in the suction line.
By convention, on suction lines of normal size and length, this is estimated as the equivalent of 2 degrees F or 1 degree C - make an adjsut ment to your calculation.

As you cannot measure it, you don't know and will have to estimate the pressure losses in the evaporator.

However if you have a Zeotropic blend (i.e. a blend with a glide) there is a further complication isofar as you will have to estimate the mean superheat for the entire evaporator.

Finally, this holds true only for an open type compressor

The total superheat of the suction gases in a hermetic system includes both the SH of the evaporator and the compressor motor. This is what the compressor has to deal with at the point of compression and is an important element in the efficiency of heat pumps.




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