basically you are measuring tempchange at the end of evaporator and suction inlet at the compressor to cold ,to much flood back of refridgerant,to warm compressor over heats an dies.use your gauges and convert presure of your refrigerant to temp
on blue gauge.hook temp probe to suction big line,on inlet of compressor and subtract both temps that will be super heat.
about 12 degrees to 22 degrees is a good super heat .on adjustable exspantion valves adjust valve ,on non adjustable
restrictors open orifice or lengthen or shorten cappilary tube or more or less charge,compressors are cooled by the return vapor
from the evap,this is the best way to diagnose any air conditioning system or refridgeration system,no super heat no charge
or bad compressor ,not enough suctionorn not enough discharge pressure,or lastly a restiction or partial restriction
which will show as no super heat and verylow suction on blue gauge and low discharge on red gauge due to a restriction.