313D Practice Exam 2 (Complete) Flashcards
With reference to a fixed orifice, can the evaporator capacity be changed by replacing the fixed orifice with another one with a smaller or larger bore diameter?
Yes, the evaporator capacity can be altered
Can you use a low pressure control as a thermostat on a system with a capillary tube metering device? Why or why not?
No, because with a capillary tube system the refrigerant pressures will equalize in the off cycle
What are 2 advantages of a capillary tube vs. a TX valve?
No moving parts and lower cost
Capillary tube capacity is based on?
Tube length, tube diameter, and pressure drop (high side to low side)
While working on a system utilizing a capillary tube metering device, you find the cap tube plugged up. The only repair is to replace the capillary tube. What other component should we also replace?
Liquid line drier
What refrigeration component should we add to a system that utilizes an automatic expansion valve?
Suction line accumulator
How does the automatic expansion valve maintain superheat in a system?
It does not maintain superheat
A TX valve is designed to maintain a constant superheat in the evaporator coil. What happens when the evaporator coil freezes over?
TX valve will not maintain superheat under all load conditions; saturated refrigerant may be getting back to the compressor
With reference to a water-cooled condensing unit, where would we install the condensing water pressure regulating valve?
Condenser water inlet connection
If you replace an internally equalized TX valve with an externally equalized TX valve, what are the consequences?
No effect on system capacity
If you replace an externally equalized TX valve with an internally equalized TX valve, what are the consequences?
Decrease in system capacity
With regards to a TX valve, if the remote bulb loses its charge, the valve will be?
Closed
One tonne of refrigeration is equal to how many BTU/min?
12,000/60=200
200 BTU/min
During a low heat load condition on a system utilizing an automatic expansion valve, the valve will?
Flood the evaporator
During a high heat load condition on a system utilizing an automatic expansion valve, the valve will?
Starve the evaporator
An automatic expansion valve is used on systems with?
Constant loads
An automatic expansion valve maintains a?
Constant suction pressure
An externally equalized TX valve senses evaporator _____?
Evaporator Outlet pressure
An internally equalized TX valve senses evaporator _____?
Evaporator Inlet pressure
Evaporator pressure exerts…?
A closing force on the TX valve
Spring pressure in a TX valve acts as…?
A closing force
The opening force of a TX valve is?
Bulb pressure
The purpose of the external equalizer on a TX valve is to?
Compensate for pressure drop in the evaporator coil
The 3 operating forces in a TX valve are?
Bulb pressure, spring pressure, and evaporator pressure
The purpose of the thermostatic expansion valve is to?
Maintain a constant superheat in the evaporator coil
While working on a system with a TX valve, you notice a suction line superheat of 20 degrees instead of 10 degrees. To decrease superheat, how do we adjust the spring stem?
In counter clockwise rotation
While working on a system with a TX valve, you notice that the suction line superheat is 3 degrees instead of 10 degrees. To increase superheat, how do we adjust the spring stem?
In clockwise rotation
What will happen if the suction line accumulator is installed backwards?
No oil will return to the compressor
The purpose of a suction line accumulator is to?
Prevent liquid refrigerant from entering the compressor while in operation
On a maintenance call, you notice that the suction pressure continually fluctuates while operating. The system has a TX valve. What could be the problem?
Sensing bulb is too large for the piping
A compressor with an internal pressure relief valve is activating while the compressor is operating. What is the best way to get the internal pressure relief to reset?
Shut the system down and let pressures equalize
While on a routine maintenance of the central air, the customer complains that when the blower starts up, there is a bad ozone smell in the house. How could we correct the problem of the electronic air cleaner being energized all the time?
Install an airflow switch in the return air and wire it in series with the EAC
When replacing a thermostat on an older system utilizing two transformers, one for cooling and one for heating, we must remember what when wiring it up ?
To remove the jumper wire between R and Rc
When installing a furnace and central air, what is the min. number of low voltage wires required to be run between the furnace control board and the thermostat?
4 wires
An externally equalized TX valve is installed in a system. Where should the remote sensing bulb be placed in relation to the equalizer line if the suction line is horizontal?
Upstream of the equalizer line
In a two-zone control system, both zones are calling for cooling, one zone damper is open, one damper is closed, and both damper motors are receiving 24 V. What is the problem?
Damper linkage is broken
What does the thermal balance point mean in relation to heat pumps?
When the heat loss of the building equals what the heat pump can produce
What is the min. evacuation reading you should get on your micron gauge before opening the condensing unit service valves?
500 microns
When evacuating a new system, the service valves are in what position?
Front-seated
While brazing, what should be running through the tubing to prevent carbon from forming inside the tubing?
Nitrogen
On a system utilizing a water-cooled condenser, what condition would contribute to high head pressure?
1. High outdoor ambient temp.
2. Coax coil has a lot of mineral buildup inside of it
3. High water flow through coax coil
4. Water is too cold going through coax coil
2.Coax coil has a lot of mineral buildup inside of it
If additional refrigerant tubing is required on a job, what type of tubing do we use?
Dehydrated refrigeration tubing
What is recommended on a vertical suction riser with the condensing unit located above the evaporator coil?
A suction line trap needs to be installed every 20 ft
What is the saturated temp. in degrees F of R22 at 58 PSIG?
32
On a call for cooling, you find the heating operating at the same time. What would be the cause of this problem?
Thermostat wiring between Y and W shorted
To correct an over-amperage of a belt drive motor we would?
Replace blower motor pulley with a smaller one
After you complete the brazing of the line set, what are the next steps to get it ready for operation?
Pressure test with nitrogen, pull a vacuum of 500 microns, release, and adjust charge
With the furnace blower motor door off, the amperage draw of the motor will be?
Above normal
What instrument would we use to measure airflow?
Anemometer
Where is a suction line drier installed after a compressor burnout?
In the line between the evaporator and the compressor
What is the purpose of the liquid line drier?
To remove debris and moisture from the system
Where is the liquid line drier installed in an AC system?
Outlet of the condenser
What would a manometer be used for in AC servicing?
To check duct static pressure
The contact of the current relay is in?
Series with the start winding
The coil of the current relay is in?
Series with the run winding
The coil of a potential relay is in?
Parallel with the start winding
The contacts in a current relay are?
Normally open
We have a system operating with a TX valve metering device without an internal bleed port, which means pressures do not equal in the off cycle. Which type of compressor is designed for this application?
Capacitor start, capacitor run
What components does a hard start kit consist of?
Potential relay and start capacitor
The electric meter you would use to check a PTCR is?
positive temperature coefficient resistor (PTCR)
Ohmmeter
Some older central AC’s were equipped with solid state PTCR devices. What were they and what was their purpose?
Positive temp. start device that aids the starting of the compressor
An air conditioning system operating with a lack of airflow across the A coil can cause? (multiple answers)
Reduced capacity, freezing evaporator coils, and premature compressor failures
What tools are required to be in compliance when de-commissioning a refrigeration system?
Recovery machine, certified cylinder, weight scales, and refrigerant record
What 2 factors affect external static pressure?
Resistance to airflow and blower speed
Define external static pressure?
Pressure drop between cold air return and the supply plenum PTO
Scroll compressors are equipped with an anti-cycle timer to prevent?
The compressor from operating in reverse direction
What is the purpose of the thermostat on a scroll compressor?
To protect the compressor from excessive discharge temperatures
You are on a service call and find the breaker keeps tripping. You find a resistance reading to ground on all compressor terminals. What do you do to correct the situation?
Replace the compressor
While checking the windings in a compressor we find an infinite reading between common and run, an infinite reading between common and start, and we get a resistance reading between start and run. What is wrong?
Open interval overload
Which two windings in a compressor will have the greatest resistance?
Start & run
Checking the windings in a compressor, between what two terminals will we have the least resistance?
Common & run
You have higher than normal suction pressure, lower than normal discharge pressure, and the compressor is drawing low amperage and is very hot. What is wrong?
Defective valves in compressor
You have higher than normal suction pressure, discharge pressure, and sub-cooling. Superheat is lower than normal. What is wrong?
Refrigerant overcharge
You have higher than normal suction pressure, low discharge pressure, and superheat is lower than normal. What is the problem?
Metering device is too large
You have lower than normal suction pressure, discharge pressure, and sub-cooling. Superheat is lower than normal. What is wrong?
Insufficient airflow across evaporator coil
You have higher than normal suction pressure, discharge pressure, and superheat. Sub-cooling is lower than normal. What is wrong with the system?
Excessive airflow beyond manufacture specs
You have higher than normal suction pressure, discharge pressure, superheat, and sub-cooling. What could be wrong with the system?
Non-condensables in the system
You are on an AC service call and find higher than normal suction pressure, low head pressure, low sub-cooling, and low superheat. The refrigerant charge is correct. What is wrong?
Oversized or no metering device orifice
You are on an AC service call and find the system is operating with low head pressure, low suction pressure, high suction superheat, and low sub-cooling. What is wrong and how do we correct the condition?
System is undercharged; recover remaining refrigerant in system, pressure test, repair leak evacuate system, and then add proper charge as per manufacture specs
What is the total capacitance of two capacitors wired in series if one capacitor is rated at 20 MFD and the other at 30 MFD, both rated at 370 VAC?
12 MFD, 740 VAC
What are the causes for a system to operate with high head pressure?
1. Refrigerant overcharge, non-condensables, and dirty evaporator coil
2. Refrigerant undercharge, non-condensables, and dirty condenser coil
3. Refrigerant overcharge, non-condensables, and dirty condenser coil
4. Refrigerant undercharge, non-condensables, and dirty evaporator coil
3.Refrigerant overcharge, non-condensables, and dirty condenser coil
Why is it important to evacuate a refrigeration system after it has been open to the atmosphere?
To remove air/non-condensables and moisture from a system
Why are resistors used on some capacitors?
To bleed the stored charge during the off cycle
What are the most common refrigerant leak detection systems?
Soap, fluorescent dyes, halide torch, and electronic leak detector
Can a heat pump switch from heating to cooling automatically?
Yes - set thermostat system switch to the auto position
What conditions will dictate a heat pump’s operation?
Indoor temp. and outdoor conditions
After a compressor burnout, where would you install a suction line drier?
In suction line just before the compressor
What type of liquid line drier is used in a heat pump?
Bi-flow
In a heat pump system, the refrigerant pressures are constant where?
Suction and discharge line to the reversing valve from the compressor
If a reversing valve is leaking internally, what systems pressures would there be?
High suction and low head pressure
A blower has a 10 inch pulley, operating at 600 rpm, and the drive pulley is 3.5 inches. What is the rpm of the blower motor?
S1 x R1=S2 x R2
1715 rpm
The 3 types of metering devices we see in residential air conditioning are?
Fixed orifice, TX valve, and capillary tube
Why should we remove the ice accumulation on an outdoor coil in the heating mode?
To increase airflow across the coil
When will the indoor coil act as a condenser?
During the heating cycle
When will the outdoor coil act as an evaporator in an air-to-air heat pump?
During the heating cycle
The small diameter line that connects the indoor unit to the outdoor unit on a heat pump is called?
Liquid line
The component that allows a heat pump to reverse its refrigeration cycle is?
Reversing valve
What is the main reason for unbalanced temperatures in a dwelling?
Unbalanced airflow in the air distribution system
The presence of non-condensable gases in a system will result in?
1. Will help increase capacity
2. Lower head pressure than normal
3. Makes no difference to the operating pressures
4. Higher head pressure than normal
4.Higher head pressure than normal
An example of two inert gases?
Nitrogen and carbon dioxide
When pressure testing an air conditioning or a refrigeration system, we use?
1. Inert gas
2. Propane
3. Compressed air
4. Oxygen
- Inert gas
Low suction pressure is a result of a lack of refrigerant in the system or not enough airflow across the A coil.
1. Makes no difference
2. True
3. False
4. None of the above
2.True
You are working on a cooler and find a blown start capacitor (230 to 280 MFD, 440 V). What start capacitor would you replace it with from your inventory on your truck?
1. 200 to 235 MFD, 330 V
2. 240 to 290 MFD, 440 V
3. 100 to 190 MFD, 330 V
4. 330 to 390 MFD, 440 V
2.240 to 290 MFD, 440 V
You are working on a central air and find a blown run capacitor (40 MFD, 330 V). Which capacitor would you use with your inventory on your truck?
1. 30 MFD, 330 V
2. 25 MFD, 440 V
3. 20 MFD, 330 V
4. 45 MFD, 440 V
4.45 MFD, 440 V
Three common types of heat pumps are?
Air-to-air, ground source, and water source
At which temp. does all molecular motion stop?
-460 degrees F
absolute zero
What components are energized in the heat pump defrost mode?
Compressor, reversing valve, and indoor blower motor
What does ERV stand for?
Energy recovery ventilator
What does HRV mean?
Heat recovery ventilator
A low pressure gas service is at a customer’s home; how far must you install the condensing unit from the meter?
0ft
How far can you install a condensing unit from a natural gas regulator?
3 ft
Low head pressure can be caused by?
1. Increased air flow over the evaporator coil
2. Increased air flow over the condenser coil with an over charge of refrigerant
3. Reduced air flow over the evaporator coil or low refrigerant
4. Reduced air flow over the condenser coil
3.Reduced air flow over the evaporator coil or low refrigerant
The factors that determine the resistance of a conductor are…?
Diameter, length, temperature, and material of the wire
Is it acceptable to replace a capacitor rated at 370 volts with one rated at 440 volts?
1. Makes no difference
2. Call an electrition
3. Yes
4. No
3.Yes
How would you charge a heat pump in the winter time?
Charge by weight
How should an evaporator A coil be drained?
Indirectly to a trapped drain
The voltage supplied to an outdoor condensing unit shall be within + or - _% the rating plate voltage?
10%
A system is operating with high head pressure, the condenser air inlet is 80 degrees F, and the condenser air outlet is 120 degrees F. What must be done to correct the situation?
1. Change blower motor
2. Clean the evaporator coil
3. Clean the condensate drain
4. Clean the condenser coil
4.Clean the condenser coil
What is the microfarad tolerance when you need to replace a capacitor?
+ or - 10%
An air conditioning system utilizing a TX valve was found to have a super heat at the compressor of 0 degrees superheat. What should be done to prevent liquid refrigeration from entering the compressor crankcase?
1. Increase refrigerant charge
2. Lower blower motor speed
3. Increase spring pressure on the TXV
4. Decrease spring pressure on the TXV
3.Increase spring pressure on the TXV
Which meter would you use to measure the specific gravity of glycol?
Hydrometer
What type of oil is used in an R134a system?
Polyol ester oil
What type of oil is used in an R410a system?
Polyol ester oil
What type of oil is used in an R22 system?
Mineral oil
What type of oil is used to lubricate electrical fan motors?
Machine oil #10
Why are suction driers made with access ports?
To check the differential pressure of the drier
In the winter, how can ice be removed from the outdoor coil on an air-to-air heat pump?
Reverse to the cooling mode
What causes an air-to-air heat pump to completely freeze up?
Defective defrost control
What are the symptoms of an internal leak on a reversing valve on a heat pump?
High suction pressure & low head pressure
From an air cooled outdoor condensing unit, what is the max. distance away that an electrical disconnect can be installed?
10 ft
Where in the refrigeration system does the refrigerant change state from a vapor to a liquid and reject heat?
Condenser
A change of state when liquid absorbs heat is called?
Vaporization
What would cause an R22 system to operate on high head pressure?
1. Increased air or water flow over the evaporator coil
2. Increased air flow over the condenser coil
3. Reduced air flow over the condenser coil
4. Reduced air flow over the evaporator coil
3.Reduced air flow over the condenser coil
Why is the air intake insulated on a HRV?
To prevent condensation from forming on the air intake pipe
What type of copper tubing is approved for ACR use?
Type L
What component permits the refrigerant to boil and absorb heat?
Evaporator
A restricting device that permits the compressor to maintain a pressure difference is called?
Metering device
