Question:Which of the following is a rarely used metering device that can be used in applications where the load is constant and an operator is present to make manual adjustments?
Answer:Automatic expansion valves.
Question:Which type of metering device is able to respond to changes in system operations?
Answer:Modulating metering device.
Question:The two general categories of metering devices are?
Answer:Fixed and modulating.
Question:Two types of fixed metering devices are:
Answer:Capillary tubes and orifices.
Question:Capillary tube metering devices are commonly used today in:
Answer:Window units.
Question:What advantages do orifice type metering devices have over capillary tubes?
Answer:They are easy to change.
Question:The most common application of the high side float controls is:
Answer:Large chillers.
Question:Automatic expansion valves are similar in operating concept to:
Answer:Pressure regulators.
Question:To increase the evaporator pressure, the adjustment on top of an automatic expansion valve should be:
Answer:Turned clockwise.
Question:Thermostatic expansion valves respond to changes in:
Answer:Superheat.
Question:Internally equalized thermostatic expansion valves measure the ___________ _____________ through a passageway inside the vale.
Answer:Evaporator Pressure.
Question:The operation of a thermostatic expansion valve can best be described as:
Answer:Bulb pressure = evaporator pressure + spring pressure
Question:Valves that open and close rapidly under the control of electronic circuits are:
Answer:Pulse modulated valves.
Question:Valves that use motors that move in tiny increments are:
Answer:Stepper motor valves.
Question:A bi-flow expansion valve:
Answer:Is designed to allow refrigerant flow in both directions.
Question:Automatic expansion valves are good at maintaining constant:
Answer:Temperature.
Question:Which metering device used on flooded evaporators opens when more refrigerant condenses, enabling the refrigerant flow into the evaporator?
Answer:High side float.
Question:Which type of metering device used on flooded evaporators opens to admit more liquid refrigerant into the evaporator when the liquid level in the evaporator drops?
Answer:Low side float.
Question:As refrigerant passes through the metering device, it:
Answer:Drops in pressure and temperature.
Question:Refrigerant leaves the metering device:
Answer:As a saturated mixture of liquid and vapor.
Question:Which of the following metering devices can respond to changes in system conditions?
Answer:Thermostatic expansion valve.
Question:In an air conditioner with a fixed metering device, a decrease in the outdoor ambient causes:
Answer:Increased system superheat.
Question:The system capacity of an air conditioner with a fixed metering device decreases or increases when the indoor wet bulb temperature rises?
Answer:Decreases.
Question:One operating advantage of fixed restriction metering devices over expansion valves is:
Answer:Can be used with low starting torque compressor motors.
Question:When the heat load on the evaporator increases, the automatic expansion valve:
Answer:Closes to keep the pressure form increasing.
Question:What is the purose of TEV sensing bulbs with a limited, or gas charge?
Answer:They produce a maximum operating pressure at high operating superheat.
Question:What senses the line temperature in electronic expansion valves?
Answer:Thermistors.
Question:Thermostatic expansion valves are designed to maintain constant:
Answer:Superheat.
Question:To increase superheat on a thermostatic expansion valve, the adjusting stem should be:
Answer:Turned clockwise.
Question:Where is the suction line temperature read when adjusting a TEV?
Answer:As close as possible to the TEV bulb.
Question:What two pieces of information are necessary to measure the TEV superheat?
Answer:The suction line temperature and pressure.
Question:What are the parts of a distributor?
Answer:A nozzle, conical divider, and multiple holes around the divider cone.
Question:Which of the following best describes the purpose of a distributor?
Answer:To equally distribute refrigerant.
Question:A device used to evenly distribute mixtures of liquid and vapor refrigerant leaving the TEV to multiple evaporator circuits is called a:
Answer:Refrigerant distributor.
Question:Besides distributing the refrigerant evenly, a refrigerant distributor also:
Answer:Creates a pressure drop across the distributor.
Question:When applied to system with air cooled condensers, what is the lowest outside ambient temperature that balanced-port valves can typically work without head pressure control?
Answer:35 degrees F
Question:What is the advantage of balanced port TEVs?
Answer:Can retain good control over a wider range of operating conditions.
Question:Why do standard design thermostatic expansion valves need a minimum pressure drop to operate correctly?
Answer:The pressure difference across the pin acts as an opening force.
Question:Which of the following problems can be caused by restrictions in the capillary tubes?
Answer:Low suction pressure.
Question:Why is it dangerous to drill out orifices in metering devices?
Answer:The orifices are conical in shape.
Question:A TEV with a dead power element will operatoe:
Answer:With a high superheat.
Question:Technicians should be careful when brazing lines to the evaporator coils that have pre-installed thermostatic expansion valves because the heat from brazing the lines:
Answer:Can overheat the TEV bulb and destroy the valve.
Question:A system with a loose TEV sensing bulb would most likely
Answer:Have a low superheat.
Question:A restricted inlet screen on a TEV can cause
Answer:low suction pressurehigh superheathigh subcooling
Question:An overfeeding metering device can cause?
Answer:High suction pressureLow superheatLow subcooling
Question:How can moisture in the refrigeration system affect the metering device
Answer:Water can freeze up at the metering device, causing a restriction.