Chapter 10 Flashcards
Temperature at which saturated vapor first starts to condense.
Dew point
Used for system pump down trapping refrigerant in the receiver enabling the technician to service the low-pressure side.
Front seated
Adding refrigerant to a system.
System charging
A service valve at the liquid receiver’s outlet.
King valve
Measured at the suction line before it enters the compressor.
System superheat
Can be accomplished using an electronic scale that can be adjusted to zero with a full cylinder.
Weighing refrigerant
Temperature at which bubbles begin to appear in a saturated liquid. Used to calculate subcooling on a system that operates with a blend.
Bubble point
Normal operating position of the valve when system is running.
Back seated
When some of the blend condenses or evaporates before the rest of the blend does.
Fractionation
Normally accomplished in the liquid line.
Liquid refrigerant charging
When a refrigerant blend has different temperatures when it evaporates and
condenses at a single given pressure.
Temperature glide
Used to add refrigerant to smaller air conditioning and refrigeration systems such as
domestic refrigerators and window or through wall air conditioners.
Graduated charging cylinder
Valve position used when charging or recovering refrigerant from a system.
Mid seated
Programmable device that will stop the charging process once the desired amount of
refrigerant has been charged.
Electric charging scale
When charging a system with a low pressure control and the control keeps shutting the compressor off, you should
a. warm the refrigerant cylinder
b. bypass the pressure control until there is sufficient pressure to keep the compressor running.
c. let the system stand for 2 hours for the pressure control to self-adjust.
d. Come back the next day.
b. bypass the pressure control until there is sufficient pressure to keep the compressor running.
Refrigerant in vapor form is normally charged into a system through the
a. liquid line
b. receiver
c. hot gas line
d. suction line
d. Suction line
When throttling in liquid refrigerant through the suction line, do not exceed ______ psig above the suction pressure to prevent liquid refrigerant from entering the compressor.
10 psig
List four items/tools required to check a system’s subcooling or superheat for the correct charge.
Thermometer, pressure gauges, curve chart, PT chart.
Bubble point is used to calculate subcooling of a blend refrigerant.
T/F
True
R-401A at a pressure of 85.3 psig has a vapor temperature of 75.08°F and a liquid
temperature of 67.79°F. It has a temperature glide of 7.29°F.
T/F
True
R-134a at a pressure of 89.3 psig has a vapor temperature of 81.7°F and a liquid
temperature of 81.7°F. It does not have a temperature glide.
T/F
True
The condensing temperature of a refrigerant blend is the average of the liquid and
vapor temperatures added together and then divided by two.
T/F
True
A system using R-407C has a discharge pressure of 125 psig and the liquid line temperature at the exit of the condenser measures 90°F. The subcooling for this system is 10°
T/F
True
Always let the system run for at least 15 minutes after recovering or adding refrigerant to a system before recalculating superheat.
T/F
True
A bathroom scale can be used to weigh a refrigerant charge into a system.
T/F
False
When working with blended refrigerants, the refrigerant must leave the cylinder as
a liquid to prevent fractionation.
T/F
True
Concentrated heat from a torch can be used to heat a refrigerant cylinder to
increase the pressure within the cylinder.
T/F
False
If the lower portion of the compressor casing becomes cold and frosty when throttling liquid refrigerant into the suction line, stop adding liquid refrigerant.
T/F
True
A unit with high super heat would indicate a ____ evaporator coil
Clogged or starved
Charging by liquid through the suction line could overload the compressor from refrigerant vapors that are too dense. What tool would you use to monitor how hard the compressor is working?
Clamp multimeter
A charging cylinder is loaded with 4 lb 4 oz of refrigerant. 28oz of refrigerant is charged into a system. How much refrigerant remains in the charging cylinder? Give your answer in pounds and ounces.
2 lb and 8 oz
To front seat a valve, turn it right or left?
Right
You are adding liquid to the suction line. As a safety precaution to prevent liquid from entering the compressor, you would place the suction service valve in the______
position.
Cracked off the back
Refrigerant cylinder pressure is 150 psig. Discharge pressure of the system is 350 psig.
Refrigerant must be charged into the system through the______ line until the pressure in the cylinder reaches____ psig.
Suction , 150 psig
When using a tub of warm water to increase pressure in the cylinder, the water temperature should not exceed____ F°
90°
Dewpoint is the temperature at which saturated vapor first starts to____.
Condense
