The hottest temperature point in a refrigeration or air conditioning system is on the back of the compressor’s discharge valve, as shown in Figure 1. However, since this point cannot be measured by a field service technician, the discharge line temperature has to be measured instead. The discharge line is shown at Point 1 in Figure 2.
The compressor’s discharge temperature can be measured by placing an insulated thermistor or thermocouple on the discharge line about 3 to 4 inches from the compressor (Point 1). The discharge temperature is a measure of the superheated refrigerant’s vapor temperature; it measures the compressor’s discharge line heat intensity, not heat content. To obtain the heat content (enthalpy), it would be necessary to know both the pressure and temperature at this point and then use a thermal dynamic superheat table for this specific refrigerant.