The discharge line exiting the compressor is the hottest part of a refrigeration or air conditioning system. The compressor’s discharge line temperature can be measured by placing an insulated thermistor on the discharge line about 3 inches from the compressor. This discharge line temperature is a measure of the superheated refrigerant’s vapor temperature. Remember, superheated refrigerant refers to a refrigerant vapor that is at a higher temperature than its saturation temperature for a certain pressure. The certain pressure would be the condensing pressure for the high side of the system in this case.