Unite 10 System Charging

Question 1

When the stem of a king valve is turned completely clockwise, closing the liquid line, it is in the _____________ position.

Answer 1

front-seated

Question 2

To perform standing pressure tests and system evacuation, a service valve should be in the ___________ position.

Answer 2

mid-seated

Question 3

The ____________ method should be used to check the charge of a system equipped with a TXV.

Answer 3

Subcooling

Question 4

The service valve position that is used for normal system operation and closes the gauge port is the ___________ position.

Answer 4

back-seated

Question 5

A system equipped with a fixed orifice metering device should be charge using the ____________ method.

Answer 5

superheat

Question 6

When working with blended refrigerants, the refrigerant must leave the cylinder as a liquid to _____________.

Answer 6

prevent fractionation

Question 7

When hot water is used to raise the pressure of a refrigerant tank, the water temperature should not exceed 120° F. true or false

Answer 7

False

Question 8

When calculating the subcooling on a system charged with a zeotropic blend, the ___________ value should be used.

Answer 8

Bubble point

Question 9

How is liquid refrigerant added to a refrigeration system when the system is out of refrigerant?

Answer 9

adding vapor or liquid refrigerant by weighing, measuring or using operating pressure charts

Question 10

How is a refrigerant cylinder pressure kept above the system pressure when the system is being charged with a vapor from a cylinder?

Answer 10

place refrigerant cylinder in 90 F water

Question 11

Why does the refrigerant pressure decrease in a refrigerant cylinder while charging with a vapor?

Answer 11

because the vapor pressure is reduced and liquid boils to replace the vapor that is leaving

Question 12

The main disadvantage of a dial scale is ….

Answer 12

it can be difficult to add refrigerant because the final cylinder weight must be calculated. The scales are graduated in pounds and ounces

Question 13

What type of equipment normally has the refrigerant charge printed on the nameplate?

Answer 13

air conditioners and refrigerated cases

Question 14

The feature of a digital electronic scale that makes them useful for refrigerant charging.

Answer 14

tare or zero

Question 15

How is refrigerant pressure maintained in a graduated cylinder?

Answer 15

heaters located on the bottom to keep refrigerant temp from dropping when vapor is pulled from the cylinder or when it is being used in cold surroundings

Question 16

How does a graduated cylinder account for volume change due to temperature changes?

Answer 16

cylinder is calibrated to ambient air temp. Refrigerant level is marked with a sliding ring.

Question 17

What methods besides weighing and measuring are used for charging a system?

Answer 17

charging charts or charging curves

Question 18

Two or more refrigerants blended together to create another refrigerant?

Answer 18

azeotropic or zeotropic

Question 19

Define temperature glide and give examples of where it happens in a refrigeration system.

Answer 19

temp glide = refrigerants that make up the blend evaporate and condense at different temps at a given pressure.

Question 20

A portion of a refrigerant blend that is evaporating or condensing before the rest of the same blend is called ….

Answer 20

fractionation

Question 21

What is the main difference between a zeotropic and an azeotropic refrigerant blend?

Answer 21

Zeotropic = has temp glide and will fractionate. Azeotropic = doesnt fractionate under normal working conditions

Question 22

What is meant by restricting liquid refrigerant into a refrigeration system when charging?

Answer 22

with zeotropic blends, refrigerant must leave the cylinder as a liquid. Once out of the cylinder, the liquid must be restricted and vaporized to avoid liquid entering the compressor

Question 23

What causes fractionation to happen in certain blends of refrigerants?

Answer 23

temperature glide = when some of the blend condenses or evaporates before the rest of the blend does

Question 24

When should a service technician use the subcooling method of charging air conditioning and heat pump systems?

Answer 24

when a TXV is used as the metering device