Central Air  PT chart Mechanical Problem 

TARGET SUPERHEAT (NON TXV). WITH TXV, SH at EVAPORATOR IS AROUND [8_12F] AND SC AROUND 25F

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  • 1. Place a thermometer on the large refrigerant pipe 6 inches from the service valve. Take the thermometer's reading, called super-heat, once it has stopped dropping.

    •     2. Find the refrigerant pressure that relates to the thermometer's reading. If the manifold's left-hand gauge has a temperature scale next to the psi scale, then use it. If not, then use a pressure/temperature chart -- called a P/T chart.

         3. Compare the super-heat reading to the gauge's psi reading. If the super-heat reading is more than 20 degrees above the P/T chart's reading, then add R-22 until the super-heating reading reaches the optimal range -- between 8- and 18-degree super-heat, depending on the environmental conditions. Many technicians charge the system until it has a 12-degree super-heat; about 70 psi at 85 F. If the super-heat reading is below 7 degrees, then the system usually has an overcharge, a stuck metering device or a dirty coil. ADD freeon Decrease SH and vice versa