What is Superheat ?
Superheat is the difference between the actual temperature of the refrigerant gas as it leaves the evaporator and the boiling point temperature of the refrigerant in the evaporator coil. After boiling, the refrigerant continues to warm up. The number of degrees it “warmed up” after boiling is called the superheat. Under worse case conditions (low load or ** orifice systems), the refrigerant in the evaporator boils off near the end of the evaporator coil. To make sure the liquid does not enter the compressor under the worse case condition (low load), the refrigerant manufactures of air conditioning equipment, publish charts indicating what superheat should be, at a given indoor wet bulb measurement and an outdoor air temperature. Superheat is your best indication on a fixed orifice system of the proper refrigerant charge. If everything else is working properly and the actual superheat is too high, add refrigerant. If it is too low, remove refrigerant. ** Orifice is a refrigerant metering device. Sometimes called a piston.**
What Is Sub-cooling ?
Sub-cooling is the difference between the boiling point of the refrigerant and the condenser, and the actual temperature of the refrigerant as it leaves the condenser. The degrees that the refrigerant cools down below the boiling point is the sub-cooling. Under worse case scenario (Low Load For Thermostatic Expansion Valve). The sub-cooling will continue to rise. If the sub-cooling rises too high, liquid may be backed into the compressor causing damage. On a thermostatic expansion valve system sub-cooling is the best indication of the state of charge in the refrigeration system, since these systems are designed to maintain constant superheat. Proper charging a system insures maximum efficiency and longer equipment life.
**Note** Proper airflow must be checked before superheat and sub-cooling.