RSES Expansion Devices 5 — Questions and Answers
Question 1: A low-side float valve opens when the liquid level in the evaporator:
- Rises above the setpoint
- Falls below the setpoint (Correct answer)
- Reaches maximum capacity
- Reaches minimum temperature
Correct answer: Falls below the setpoint
When liquid level drops, the float falls and opens the valve to admit more refrigerant, maintaining the correct flooded level.
Question 2: Which factor primarily determines the refrigerant flow capacity of a capillary tube?
- Tube material composition
- Tube length and inside diameter (Correct answer)
- Ambient temperature only
- Refrigerant color and viscosity
Correct answer: Tube length and inside diameter
Capillary tube flow capacity is determined by its length and inside diameter, with shorter/larger diameter tubes passing more refrigerant.
Question 3: An electronic expansion valve (EEV) in a variable refrigerant flow (VRF) system is typically controlled by:
- A mechanical sensing bulb
- A microprocessor receiving inputs from multiple sensors (Correct answer)
- A manual pressure regulator
- Direct high-side pressure feedback only
Correct answer: A microprocessor receiving inputs from multiple sensors
EEVs in VRF systems are controlled by microprocessors using inputs such as suction superheat, coil temperature, and load demand for optimal performance.
Question 4: When replacing a TXV, which specification is most critical to match?
- Valve body color and brand
- Refrigerant type, capacity rating, and evaporator temperature range (Correct answer)
- Connection thread pitch only
- Manufacturer part number suffix letter
Correct answer: Refrigerant type, capacity rating, and evaporator temperature range
The replacement TXV must be rated for the same refrigerant, system capacity, and operating temperature range to ensure proper performance.
Question 5: What symptom would a refrigeration technician observe if the TXV sensing bulb loses its refrigerant charge?
- TXV opens fully, flooding the evaporator
- TXV closes fully, starving the evaporator (Correct answer)
- TXV operates normally with slight superheat error
- High-side pressure drops dramatically
Correct answer: TXV closes fully, starving the evaporator
Without bulb pressure as the opening force, the spring pressure keeps the TXV closed, starving the evaporator and causing high superheat.
Question 6: The short-tube orifice (fixed orifice) expansion device is commonly used in which type of system?
- Large industrial chillers
- Residential heat pumps with scroll compressors (Correct answer)
- Flooded shell-and-tube evaporators
- Variable-capacity commercial refrigeration
Correct answer: Residential heat pumps with scroll compressors
Short-tube orifices are widely used in residential heat pumps because they allow bidirectional flow needed for heating and cooling mode switching.
Question 7: Technician A says superheat should be measured at the evaporator outlet. Technician B says superheat should be measured at the compressor inlet. Who is correct?
- Technician A only
- Technician B only
- Both technicians, depending on what is being measured (Correct answer)
- Neither technician
Correct answer: Both technicians, depending on what is being measured
Evaporator superheat is measured at the evaporator outlet for TXV adjustment, while total (compressor) superheat is measured at the compressor inlet for overall system evaluation.
RSES Expansion Devices 5
A low-side float valve opens when the liquid level in the evaporator: