Modern Chap 21: Review questions

Question 1

The simplest type of the following metering devices is

a) thermostatic expansion valve
b) automatic expansion valve
c) low-side float
d) capillary tube

Answer 1

d) capillary tube

Question 2

_____________ metering devices automatically change their orifice sizes to account for changes in load

a) adsorption
b) equalizer
c) fixed
d) modulating

Answer 2

d) modulating

Question 3

Which of the following statements regarding capillary tubes is not true?

a) it equalized pressure between the high and low side during the off cycle
b) it works with the suction line as a heat exchanger for improved system efficiency
c) having a proper refrigerant charge is less critical in a system with a capillary tube than it is in a system with a thermostatic expansion valve
d) it’s performance is determined by its inside diameter, its length, and the number of turns

Answer 3

c) having proper refrigerant charge is less critical in a system with a cap tube than it is in a system with a thermostatic expansion valve

Question 4

A ________ is a fixed-orifice metering device that consists of a fitting with a hole between the fittings inlet and outlet

a) metering orifice
b) electronic expansion valve
c) heat exchanger
d) equalizer

Answer 4

a) metering orifice

Question 5

The top of a thermostatic expansion valves diaphragm is exposed to ________, which works to close to the valve

a) atmospheric pressure
b) high side pressure
c) low side pressure
d) sensing bulb pressure

Answer 5

d) sensing bulb pressure

Question 6

The purpose of a bleed valve or bleed port in a thermostatic expansion valve is to

a) ensure that the underside of the diaphragm is exposed to the same pressure as the evap outlet
b) equalize low-side and high-side pressure during the off cycle
c) reduce valve hunting during operation
d) vent refrigerant to the atmosphere if high-side pressure becomes excessive

Answer 6

b) equalize low-side and high-side pressure during the off cycle

Question 7

Which of the following types of sensing bulbs are charged with the same type of refrigerant used in the system;

a) gas-charged and adsorption gas cross-charged
b) gas-charged and gas cross-charged
c) liquid-charged and gas-charged
d) liquid-charged and liquid cross-charged

Answer 7

c) liquid-charged and gas-charged

Question 8

A mechanical pressure limiter or a __________ can be used to limit the maximum operating pressure (MOP) of a thermostatic expansion valve

a) liquid charged sensing bulb
b) liquid cross-charged sensing bulb
c) gas-charged sensing bulb
d) all of the above

Answer 8

c) gas-charged sensing bulb

Question 9

Which of the following statements regarding automatic expansion valves is not true?

a) An AXV closes as evaporator pressure rises and opens as evaporate pressure drops
b) automatic expansion valves must be adjusted for atmospheric pressure
c) the evaporator of a system equipped with a properly operating automatic expansion valve will not become entirely filled with liquid refrigerant
d) sensing bulb pressure acts to close the valve and low-side pressure acts to open the valve

Answer 9

d) sensing bulb pressure acts to close the valve and low-side pressure acts to open the valve

Question 10

Which of the following statements regarding stepper motor EEV’s is not true?

a) it’s controller will occasionally fully close the valve by sending the stepper motor more step signals than it can use
b) a stepper motor can rotate in small, precise, and repeatable increments
c) a stepper motor EEV has a gear train and threaded piston they convert the motors rotation into linear movement of the valve
d) a stepper motor regulates flow as it responds to a PWM signal by opening and closing rapidly

Answer 10

d) a stepper motor regulates flow as it responds to a PWM signal my opening and closing rapidly

Question 11

A ________ varies refrigerant flow by varying the speeds at which a solenoid-operated valve opens and closes

a) dual-pressure EEV
b) float-operated EEV
c) pulse-width modulating EEV
d) variable-frequency solenoid EEV

Answer 11

c) pulse width modulating EEV

Question 12

Which of the following statements regarding a low-side float system is not true?

a) the evaporator has a large receiver that holds liquid refrigerant
b) the float can be a sealed ball or an open pan
c) the high-side and low-side pressures balance during the Off cycle
d) these systems are often referred to as flooded systems

Answer 12

c) the high-side and low-side pressures balance during the off cycle

Question 13

Which device is used to reduce pressure drop across a large evaporator?

a) bleeder or bypass
b) distributor
c) heat exchanger
d) pressure limiter

Answer 13

b) distributor

Question 14

In heat pump systems, which metering device uses a moveable piston that allows full flow in one direction and causes a pressure drop for flow on the other direction?

a) automatic expansion valve
b) capillary tube
c) metering orifice
d) thermostatic expansion valve

Answer 14

c) metering orifice

Question 15

A high-side float is a float-type metering device that regulates refrigerant flow into the evaporator based on the _________ of liquid refrigerant in the high-side receiver

a) pressure
b) sub cooling
c) temperature
d) volume

Answer 15

d) volume

Question 16

List the three variables that affect capillary tube performance. Explain how each of these variables affects performance:

Answer 16

Tube length - longer tube = greater pressure drop

Inside diameter - smaller diameter = greater pressure drop

Number of turns - more turns = greater the pressure drop

Question 17

What is the advantage of recent capillary tube designs having a larger diameter and being longer than older designs?

Answer 17

less likely to become plugged cause of the diameter and longer length

Question 18

What is initialization?

Answer 18

An over driving routine in which a controller, when first powered, will send an electronic expansion valve (EEC) more steps than the valve can use

Question 19

What is the purpose of a bleed port on a refrigeration metering device? How does this affect the compressor?

Answer 19

equalize low-side and high-side pressure during the Off cycle

could cause migration

Question 20

explain why oil binding is less troublesome in high-side float systems than in low-side float systems.

Answer 20

At higher pressure, the oil dissolves and circulates more readily in the liquid refrigerant