If the thermal bulb of an expansion valve is incorrectly placed at the center of the evaporator coil instead of the end (tail coil), it will have which of the following effects?
• Thermostatic expansion valve (TXV) sensing bulb function • Effect of bulb location on sensed superheat at the end of the evaporator • Relationship between superheat control and refrigerant flow through the evaporator
• Think about what the bulb is supposed to measure at the outlet of the evaporator and why that matters for compressor protection • If the bulb is moved to the center of the coil, will it see more liquid, more vapor, or a different amount of superheat than at the tail end? • How would an incorrect superheat reading cause the valve to adjust refrigerant flow—would it tend to open more or close more?
• Be clear on what superheat means: temperature of vapor above its saturation temperature at that pressure • Visualize where the last bit of liquid refrigerant normally boils off: near the tail end of the evaporator, not the middle • Ask: if the bulb senses a condition that looks "more comfortable" (less risk of liquid) than actually exists at the outlet, does the valve tend to overfeed or underfeed the evaporator?
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