When I measure superheat I will put my temp. probe in the discharge air and wait till the temp. reaches its lowest point. Then mount the temp probe about 3" on the suction line on the outlet of the evap. coil. I will wait for the txv to open and note the temp. at wich it bottoms out at. This is the temp. I use to subtract from SST! On the smaller stuff ( self contained) I have been working on lately the txv seems to never open enough to get that drop temp. When I say smaller stuff as opposed to open 8 and 12" supermarket cases. How accurate is your superheat reading if the temp. taken isn't at the bottom temp?