To accurately measure aircon superheat, you’ll need the equipment, a pressure gauge, a thermometer or thermocouple to measure suction line temperature, and a refrigerant pressure-temperature (P-T) chart. The P-T chart helps determine the refrigerant’s boiling (saturation) temperature at the measured pressure, allowing you to calculate the superheat. 

Here are the details of equipment usage:

1. Pressure Gauge: 

• Measures the suction (low-side) pressure of the refrigerant.
• Commonly, a gauge manifold is used, especially for measuring pressure and temperature simultaneously.

2. Thermometer or Thermocouple:

• Measures the suction line temperature, which is the temperature of the refrigerant vapour. 
• A clamp-on thermometer or thermocouple provides accurate measurements. 

3. Refrigerant Pressure-Temperature (P-T) Chart: 

• This chart is specific to the refrigerant being used.
• It shows the relationship between pressure and saturation temperature for the refrigerant.

How to Measure Superheat:

1. Measure Suction Pressure:

1. Attach a pressure gauge to the suction line service port and record the reading. 

2. Measure Suction Line Temperature:

2. Attach a thermometer or thermocouple to the suction line near the suction gauge port and record the reading. 

3. Find Saturated Temperature:

3. Using the P-T chart for the refrigerant, find the saturation (boiling) temperature corresponding to the measured pressure. 

4. Calculate Superheat:

4. Subtract the saturation temperature from the suction line temperature. 

Example: 

• If the suction pressure is 30 psig and the refrigerant is R-22, the P-T chart might indicate a saturation temperature of 70°F.
• If the suction line temperature is 75°F, the superheat would be 5°F (75°F – 70°F).