Unit 10 Flashcards
Scale that can be adjusted to zero with a full cylinder
electronic scale
Typically used in conjunction with fixed bore metering devices if superheat measurements are shown. Charging curves that rely on subcooling are typically used on systems with a TXV
charging curves
Temperature at which saturated vapor first starts to condense
dew point
When some of the blend condenses or evaporates before the rest of the blend does
fractionation
Used for system pump down. Trapping refrigerant in the receiver enabling technician to service the low pressure side
front seated
Used to add refrigerant to smaller air conditioning and refrigeration systems, such as domestic refrigerators and window or through the wall air conditioners
graduated charging cylinder
A service valve at the liquid receiver’s outlet in the refrigeration system
king valve
Measured at the suction line before it enters the compressor
system superheat
Accomplished by allowing vapor to move out of the vapor space of a refrigerant cylinder and into a refrigeration system
vapor refrigerant charging
Used for performing standing pressure tests and for system evacuation or charging
midseated
Normally accomplished in the liquid line
liquid refrigerant charging
Normal operating position of the valve when system is running
back seated
Adding refrigerant to a system
system charging
May be accomplished using various scales. Bathroom scales should not be used
weighing refrigerant
T/F
The correct way to charge a unit that is low on refrigerant is to recover the remaining charge, compare it to the data plate and then recharge the unit plus the amount that was missing to equal the total charge on the data plate
True
T/F
System readings can be taken immediately after adding or recovering refrigerant
False
T/F
Bubble point and dew point apply to pure refrigerants
False
T/F
The further away from the compressor, the lower the temperature of the liquid line
True
T/F
To calculate superheat, subtract the temperature at the exit of the evaporator from the internal temperature of the evaporator
False
Front seating the king valve on the receiver prevents liquid refrigerant from reaching the metering device
True
T/F
The electric plug on a charging cylinder is used to heat the refrigerant to keep the pressure from dropping when vapor is being removed from the cylinder
True
T/F
Once system pressure is equal to the refrigerant cylinder pressure, charging is complete
False
T/F
To charge a system with liquid refrigerant, always turn the cylinder upside down
False. If using a new cylinder, liquid comes from the bottom
T/F
The further away from the evaporator, the lower the temperature of the suction line
False. It picks up superheat along the lines
T/F
Fractionation happens only when the leak occurs as a vapor leak
True
To start a system that uses a low-pressure control, _______________
D. (answers B&C)
Place a jumper wire across the low pressure contacts and/or use a screwdriver to close the low pressure control contacts
Service valves that have their stems turned all the way clockwise into the valve are referred to as
front seated
When large amounts of refrigerant are needed, adding the liquid through the ____________ is preferable to other methods because it saves time
king valve on the receiver
The king valve has four positions. What are they?
Front seat, mid seat, back seat and cracked off the back
Why must refrigerant be added to the suction side of the system when the system is running?
This is to top off charge according to spec. The high side pressure while in operation will not allow refrigerant to exit the cylinder. While in operation, the vacuum will suck refrigerant into the system
How can liquid refrigerant be charged into the suction line without damaging the compressor
You may use a commercial liquid line restrictor. You can also crack the service valve off the back and throttle the manifold gauge no more than 10 psig
Use supplied system charging chart to determine subcooling, more or less refrigerant, type of metering device given the scenario
Refer to charging chart plate example
Be able to determine subcooling/superheat based on scenario given
What is the formula for estimating condensing pressure for a high efficiency/micro channel condensing unit?
High- add 30 degrees F to the ambient temp to get internal temp of condenser and convert to psig.
Micro channel- add 15 degrees F to ambient to get internal and convert
Noncondensables in a system can cause what types of problems in a system?
This will cause moisture which can result in acid and sludge. The system can also have higher pressures resulting in system inefficiency
What does the gas ballast feature on a vacuum pump do?
It allow a measure of atmospheric pressure to balance when pulling vacuum. This extends the life of pump and oil
T/F
When checking superheat on a unit that uses refrigerant blend, use the bubble point figures
False
