If the evaporator coil horizontal return line of a refrigeration system is less than 7/8" (2.21 cm) in diameter (considered small), which figure in the illustration represents the proper orientation and placement of the thermostatic expansion valve sensing bulb? Illustration RA-0049
• Thermostatic expansion valve (TXV) bulbs must sense true suction line temperature, not oil or stratified refrigerant • For small suction lines (< 7/8 in.), bulb mounting recommendations are different from those for larger lines • Consider the "clock position" around the pipe (12, 3, 6, 9 o'clock) and any influence from the nearby liquid line
• On a small horizontal suction line, where around the pipe will the refrigerant be most uniformly mixed, rather than pooling as liquid or oil? • Which figure shows the bulb making good contact on clean pipe surface, not touching or being shaded/heated by the liquid line? • Compare the clock positions in A–D: which one matches the standard recommendation for bulbs on small-diameter horizontal suction lines in HVAC/R texts?
• Make sure the bulb is firmly clamped with maximum metal-to-metal contact on the suction line • Verify the bulb is on the suction line only, not bridging suction and liquid lines or touching the liquid line • Confirm the bulb’s clock position matches the guideline for small (< 7/8 in.) vs. large suction lines (these use different recommended angles)
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