🔍 Key Concepts

• Thermostatic expansion valve (TXV) purpose and how it is controlled • Location and function of the power element (power head/bulb) on a TXV • Relationship between sensed temperature and bulb pressure in a charged element

💭 Think About

• Where is the sensing bulb of a TXV physically attached in most marine refrigeration systems, and what does that tell you about what it is actually measuring? • Which factor will most directly change the pressure of the fluid inside the power element: box air temperature, refrigerant condition at the coil outlet, suction pressure at the compressor, or general heat transfer in the evaporator? • Think about what the TXV is trying to control: is it reacting to conditions inside the box, or to the refrigerant condition leaving the evaporator?

✅ Before You Answer

• Identify what the sensing bulb is strapped to and what temperature it sees. • Separate air temperatures (in the box) from refrigerant line temperatures (on the evaporator outlet). • Verify that compressor suction pressure is a result of valve operation, not the direct control signal to the power element.