Unite 10 System Charging Flashcards
When the stem of a king valve is turned completely clockwise, closing the liquid line, it is in the _____________ position.
front-seated
To perform standing pressure tests and system evacuation, a service valve should be in the ___________ position.
mid-seated
The ____________ method should be used to check the charge of a system equipped with a TXV.
Subcooling
The service valve position that is used for normal system operation and closes the gauge port is the ___________ position.
back-seated
A system equipped with a fixed orifice metering device should be charge using the ____________ method.
superheat
When working with blended refrigerants, the refrigerant must leave the cylinder as a liquid to _____________.
prevent fractionation
When hot water is used to raise the pressure of a refrigerant tank, the water temperature should not exceed 120° F. true or false
False
When calculating the subcooling on a system charged with a zeotropic blend, the ___________ value should be used.
Bubble point
How is liquid refrigerant added to a refrigeration system when the system is out of refrigerant?
adding vapor or liquid refrigerant by weighing, measuring or using operating pressure charts
How is a refrigerant cylinder pressure kept above the system pressure when the system is being charged with a vapor from a cylinder?
place refrigerant cylinder in 90 F water
Why does the refrigerant pressure decrease in a refrigerant cylinder while charging with a vapor?
because the vapor pressure is reduced and liquid boils to replace the vapor that is leaving
The main disadvantage of a dial scale is ….
it can be difficult to add refrigerant because the final cylinder weight must be calculated. The scales are graduated in pounds and ounces
What type of equipment normally has the refrigerant charge printed on the nameplate?
air conditioners and refrigerated cases
The feature of a digital electronic scale that makes them useful for refrigerant charging.
tare or zero
How is refrigerant pressure maintained in a graduated cylinder?
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
How does a graduated cylinder account for volume change due to temperature changes?
cylinder is calibrated to ambient air temp. Refrigerant level is marked with a sliding ring.
What methods besides weighing and measuring are used for charging a system?
charging charts or charging curves
Two or more refrigerants blended together to create another refrigerant?
azeotropic or zeotropic
Define temperature glide and give examples of where it happens in a refrigeration system.
temp glide = refrigerants that make up the blend evaporate and condense at different temps at a given pressure.
A portion of a refrigerant blend that is evaporating or condensing before the rest of the same blend is called ….
fractionation
What is the main difference between a zeotropic and an azeotropic refrigerant blend?
Zeotropic = has temp glide and will fractionate. Azeotropic = doesnt fractionate under normal working conditions
What is meant by restricting liquid refrigerant into a refrigeration system when charging?
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
What causes fractionation to happen in certain blends of refrigerants?
temperature glide = when some of the blend condenses or evaporates before the rest of the blend does
When should a service technician use the subcooling method of charging air conditioning and heat pump systems?
when a TXV is used as the metering device
