To do this, it keeps the coil supplied with the proper amount of refrigerant to maintain the right superheat of the suction gas leaving the evaporator.
Because good superheat control is the criterion of TEV performance, accurate measurement is vital.
Step A: Determine the suction pressure at the evaporator outlet with an accurate gauge. If there is no gauge connection, a tee installed in the valve’s external equalizer line can be used.
Step B: Refer to a temperature-pressure chart for the refrigerant used in the system, and determine the saturation temperature at the observed suction pressure.
Step C: Measure the temperature of the suction line at the remote sensing bulb location. This can be accomplished by a strap-on thermometer or an electric device similar to an “Annie” or “Simpson” meter.
Be certain the spot chosen for measurement is clean to help ensure accurate readings.
Step D: Subtract the saturation temperature determined in Step B from the suction gas temperature measured in Step C. The difference is the operating superheat.
Our experience has shown that an externally equalized valve should be used whenever pressure drop through the evaporator reaches:
On this basis, an externally equalized valve would automatically be the selection for any system in excess of 3 tons, regardless of the application.
Figure 3 shows the ideal placement (horizontal) of the bulb in relation to suction line size. Never put the bulb at 6 o’clock because it may sense the temperature of the oil flowing through the pipe, rather than the temperature of the refrigerant.
Finally, be sure the bulb location is on a free-draining suction line.
Choosing the proper TEV for the specific system remains the first step in good service — and no callbacks.
Publication date: 08/21/2000