313D Practice Exam 1 (Complete) Flashcards
What is the principal function of the expansion tank in a hot water system?
It allows the volume of the water in the system to change to maintain working pressure
What must be verified before replacing the electronic control board if the onboard diagnostics fault is incorrect?
Verify power supply and all inputs, outputs, and loads are properly connected and true
Which three instruments are required to check the calibration of an enthalpy control on the economizer of a rooftop air conditioning unit?
Thermometer, sling psychrometer, and multimeter
What would be the min. VA requirements for a 24 VAC transformer powering four thermal electric expansion valves with a resistance of 150 ohms across each heater?
15.4 VA
Which method is used to determine approach of a cooling tower?
Measure the temp. difference of the water leaving the tower and the wet bulb temp. of the air entering the tower
What is the air velocity if a pitot tube connected to an inclined manometer gauge reads 0.2” water column?
1791 fpm
What is the probable cause of high suction pressure on a heat pump?
1. An outdoor thermostatic expansion valve malfunction
2. A leaking four-way valve
3. A leaking liquid line solenoid
4. Low refrigerant charge
A leaking four-way valve
When testing a compressor motor winding with a megger, what reading would indicate a good, clean system?
100 megaohms
If the pressure differential across the circulating pump is 21.65 psi, how many metres (feet) of head is the pump capable of lifting?
multiply the pressure pounds per square inch by 2.31
21.65 x2.31=50ft
15.2 m (50.00 ft)
What is the cooling capacity of a water chiller operating with a 4.4 C (40 F) evaporating temp., return water temp. of 10 C (50 F), and a 7.2 C (45 F) supply water temp. if the water flow rate is measured at 910 L/min (200 gal/min)?
146500 W (500,000 BTU/h)
BTU = Flow Rate In GPM (of water) x (Temperature Leaving Process - Temperature Entering Process) x 500
What would be the problem on a time-initiated, temperature-terminated defrost if the defrost cycle runs full time during periods of light coil frosting?
Faulty defrost thermostat
When diagnosing the motor windings of a hermetic compressor, the following values are noted:
- common-to-start: 18 ohms
- start-to-run: 21 ohms
What should the common-to-run value be?
3 ohms
What is an indication of a plugged metering device?
- Low suction pressures
- High superheats
- Low head pressures
- High subcooling
- Low amp draws
When constructing a walk-in freezer box, where should the vapour barrier be installed?
Outside on the warmest side
What is the cooling capacity of a water chiller operating with a 4.4 C (40 F) evaporating temp., return water temp. of 10 C (50 F), and a 7.2 C (45 F) supply water temp. if the water flow rate is measured at 682.5 L/min (150 gal/min)?
109875 W (375,000 BTU/h)
BTU = Flow Rate In GPM (of water) x Temp Rise (Temperature Leaving Process - Temperature Entering Process) x 500
BTUs =150 x 5(50-45) x 500
BTUs=375,000
What amperage capacity should the supply wiring be rated for a refrigerated fixture which has a 208 V power supply and the following loads?
- 4 evaporator fan motors rated at 9 W each
- 2 defrost heaters rated at 6 A each
- 6 fluorescent lights rated at 40 W each
- 1 strip mullion heater rated at 3 A
20A
What is the min. required hole size to accommodate a 30 mm (1 in.) O.D. copper pipe with 20 mm (3/4 in.) insulation?
70 mm (2 5/8 in.)
What is the min. required sleeve size when installing a 50 mm (2 in.) nominal pipe with 38 mm (1 1/2 in.) insulation through a 200 mm (8 in.) concrete block exterior wall?
150 mm (6 in.)
How should a load be lifted with a wrap-around sling when crushing of the load is a major concern?
Place a spreader above and below the load
Concerning hermetic compressors, when does the compressor draw from the evaporator?
Mostly during the suction stroke
Potential relay contacts are closed by?
The loss of counter EMF
If a system has a “non-bleed” type TXV, what should be installed?
A hard start kit
Power loss in a motor is converted to heat energy?
1. True
2. False
- True
What will happen if a metering device is too permissive? (Multiple answers)
- Super heat will decrease
- Suction pressure will increase
- Head pressure will decrease
- Sub cooling will decrease
What should be reconsidered when an evaporator is 65 ft lower than the condenser?
Liquid line diameter
Which of the following can cause an evaporator to freeze-up?
1. Reversing valve leaking internally
2. Clogged condenser
3. Bypass type humidifier
4. Oversized furnace blower motor
3.Bypass type humidifier
The force that drives a reversing valve to shift is?
The system pressures
A technician is replacing a faulty compressor contactor. The one that is being replaced is a single pole. The one that is being installed is a double pole. How should an “off-cycle-self-regulating” crankcase heater be connected to this new 2 pole contactor?
- One wire to the line side of one of the poles, one wire to the load side of the other pole, then reroute the line wire of the opposing pole to the load side of the contactor
- Both wires to the line side of the contactor
- Both wires to the load side of the contactor
- One wire to the line side of one of the poles, the other wire to the load side of the same pole, then reroute the compressor wire of the opposite pole to its line side
- One wire to the line side of one of the poles, the other wire to the load side of the same pole, then reroute the compressor wire of the opposite pole to its line side
When using flux, what is the visual clue that you can now apply the filler alloy?
The flux has become a clear liquid
What can happen to the pressure during the heat pump cooling mode if a zone damper that fails to open
Can cause low suction pressure for heat pump cooling mode
A reversing valve that has an internal leak will?
1. Causes the compressor to overheat
2. Decreases the liquid temp. in the condenser
3. Decreases compressor amperage
4. Increases the liquid temp. in the evaporator
5. All of the above
6. None of the above
5.All of the above
Because of heat of compression, condensers must reject more heat than evaporators absorb?
1. True
2. False
1.True
What would you not find on a typical air source heat pump? (outdoor unit)
A blower relay
CFC refrigerants are so stable they act as “carriers” that store chlorine until they reach the atmosphere where they then release the ozone depleting chlorine?
1. True
2. False
1.True
What is the most dangerous to use for pressure testing?
Oxygen
Is it ever acceptable and proper to install an “A” coil in the return air plenum of a furnace?
Yes, if the installation is a heat pump added on to an existing electric forced air furnace
Which of the following statements is true?
1. Liquid lines have less heat content in them than the suction lines
2. Hot gas discharge lines have the greatest heat content
3. Liquid lines should be warmer than suction lines
4. All of the above
5. None of the above
4.All of the above
If an R22 system has a suction pressure of 15 PSIG and a head pressure of 120 PSIG and the temp. of the suction line is 73 F and there is a small amount of frost at the end of the cap tunes, what is the problem?
Major loss of charge
Relays, while they can have numerous poles, can have no more than 2 throws?
1. True
2. False
1.True
What happens when fresh air from outside is brought in for ventilation purposes?(multiple answers)
- It usually humidifies the building in the summer time AND dehumidifies the building in the winter time
- It usually increases latent load for air conditioning
- It must be filtered
Motors convert electricity to strong, moving, rotating, magnetic fields?
1. True
2. False
1.True
CFC’s are very stable; one of the only things that can break them down is UV radiation?
1. True
2. False
1.True
What will cause liquid refrigerant to load up in the condenser?
A metering device that is too restrictive AND a cold condenser ambient
As humidity rises, the air temp. difference across an evaporator coil?
1. Increases
2. Decreases
2.Decreases
What must youy do if the interconnecting line set is greater than the standard length?
Consult the manufacture installation manual for guidelines
What will be the approximate R22 liquid pressure at the metering device inlet if the liquid line rises 50 ft and the pressure at the condenser outlet is 200 PSIG? (assume 100 F)
173 PSIG
Where do the reversing valves pipes go?
Have two pipes connected to the compressor, one connected to the condenser, and one connected to the evaporator
What would you not find on a typical ground source heat pump?
A defrost control
Low suction pressure can be caused by?
1. A TEV that is stuck nearly shut
2. A TEV that is stuck wide open
3. Poor compressor valves
4. None of the above
1.A TEV that is stuck nearly shut
On a TXV, the high side liquid pressure exerts a ____ influence on the valve?
Opening
On a TXV, evaporator pressure exerts an _____ influence on the valve?
Closing
On a TXV, the sensing bulb exerts _____ influence on the valve?
Opening
The equalizer line on a TXV is generally 1/4 inch OD and it connects to the?
Suction line and conveys evaporator outlet pressure to the bottom of the valve’s diaphragm, giving a closing influence to the valve
The ohm readings taken from a hermetic compressor are
- 12 ohms from R to ground
- 6 ohms from C to ground
- 6 ohms from S to ground
- 18 ohms from R to S
- 6 ohms from R to C
- 12 ohms from S to C
1. There is a small short to ground halfway through the common winding
2. The compressor has a small short to ground halfway through the run winding
3. There is a small short to ground halfway through the start winding
4. There is a small short to ground in the internal overload
3.There is a small short to ground halfway through the start winding
Copper tubing glows with a red/brass colour at?
1800 F
If indoor dry bulb is 73 F and WB is 68 F and the customer complains that they do not feel comfortable?
- Perhaps the system is oversized
- Perhaps the air flow through the evaporator is too fast
Which of the following is a control that can solve low head pressure problems?
1. CCH
2. GPM
3. HRV
4. LAC (low ambient control)
4.LAC (low ambient control)
To recycle refrigerant is to?
Remove it from a system, clean it for reuse by filtering it repeatedly though filter/driers
Fuses are safety devices which?
Shut down a circuit during excessive current
Fuses are always connected in series to the load?
1. True
2. False
- True
Motors, briefly during startup will…? (multiple answers)
- Draw high amperage
- Cause a voltage drop
Typical single phase induction motors have a start winding which is automatically disconnected shortly after startup?
1. True
2. False
1.True
A mechanically seized air conditioning compressor draws?
LRA
The heat pump defrost cycle is simply the cooling cycle…?
1.With the outdoor fan temporarily shut off
Volumetric efficiency increases when?
Head pressure decreases
The purpose of a crankcase heater is? (multiple answers)
- To keep compressor pressure high when the system is off
- To keep liquid refrigerant from accumulating in the compressor
- To keep the motor windings active
If the evaporator coil is damaged, you should?
Replace the evaporator coil
If the condenser coil is damaged, you should?
Replace the condenser coil
In a four wire control system, what 2 terminals will have a jumper at the thermostat?
Rc and Rh
The capacitor must be within _% of the rating on the label?
10
If heating and cooling mode are both running at the same time, what is the most likely problem?
Shorted thermostat
Capacitors 20 MFD @ 370 VAC and 15 MFD @ 370 VAC wired in parallel equal?
35 MFD @ 370 VAC
Capacitors 20 MFD @ 370 VAC and 15 MFD @ 370 VAC wired in series equal?
8.6 MFD @ 740 VAC
Potential relay contacts are opened by?
The increase of counter EMF from the start winding
What is the difference between an HRV and an ERV?
An ERV recovers both latent and sensible heat, but an HRV only recovers sensible heat
Shortly after the installation of an electronic air cleaner (EAC), a customer complains that there is a noticeable, irritating ozone smell in the hall of the house. Which of the following is a possible cause of this problem?
The installing technician may have neglected to interlock the EAC with the blower
When condenser air flow is poor what happens to the suction pressure?
Suction pressure will usually increase
What system pressures would be typical for the following conditions?
Refrigerant: R22
Metering: Orifice
OD temp: 80 F DB - 71 F WB
ID temp: 74 F DB - 62 F WB
75/225 PSIG
Which of the following can cause compressor RLA to rise?
1. A failed compressor crankcase heater
2. Poor evaporator air flow
3. A faulty cooling anticipator
4. Poor condenser air flow
4.Poor condenser air flow
An uninsulated suction line will cause liquid refrigerant to flow to the compressor?
1. True
2. False
2.False
The “C” terminal is…?
Is constantly energized with 24 VAC (often grounded or common)
The “Y” terminal is…?
Is energized only during a call for compressor
The “R” terminal?
Is energized with 24 VAC (ungrounded)
A residential gas furnace typically uses which breaker?
A 1 pole, 15 amp breaker
What is the best way to test the limit switch on a furnace after having installed a fan control center?
Disable the blower, set the thermostat to call for heat, and set the fan switch to the “on” position
Most HVAC thermostats?
1. Convert magnetism to electricity for safe control of high power loads
2. Convert electricity to magnetism for safe control of high power loads
3. Use low voltage from the primary of the control transformer to safely control high power loads
4. Use low voltage from the secondary of the control transformer to control high power loads
4.Use low voltage from the secondary of the control transformer to control high power loads
Which of the following is a vacuum measurement?
1. 29.9 in. Hg.
2. 29.9 PSIA
3. 29.9 PSIG
4. Any of the above
5. None of the above
- 29.9 in. Hg.
Which refrigerant is becoming the industry accepted replacement for R22?
R410a
In air conditioning, a lower suction pressure can be caused by?
1. High humidity
2. Undersized ductwork
3. Clogged condenser coil
4. All of the above
5. None of the above
2.Undersized ductwork
On a TXV, the spring exerts an ____ influence on the valve?
Closing
The middle tab on the dial of a conventional fan/limit control is the setting for?
Turning the fan on
When installing air conditioning on an old furnace you will need to? (multiple answer)
- Check for a 40 VA transformer and install one if none is present
- Check for a blower relay and install one if none is present
- Test all safety devices when the installation is complete
- Consider installing an isolation relay
- Check the fan motor horse power and consider installing a larger motor and pulley6.All of the above
Heat anticipators are connected in series with…?
They’re connected in series with the gas valve
The conventional fan/limit combination control?
- Has normally open contacts on the fan side
- Has normally closed contacts on the limit side
- Has a common, removable jumper connecting together the line side of both contacts
- Is thermally driven
The wiring in most residential breaker panels is?
240/120 VAC, 1 phase, 60 Hz.
Electromotive force is measured with?
A volt meter
When checking continuity be sure to?
Disconnect power from the circuit so that voltage does not damage the meter
Electrons?
1. Are + charges
2. Are - charges and repel each other
3. Repel protons
4. Are + charges and repel protons.
5. Repel each other
6. Are - charges
2.Are - charges and repel each other
Electricity is the flow of?
Valence electrons
Condensate drain lines must be…?
Must be indirectly draining into a trapped drain
The suction saturation temp. of an air source heat pump is? (heating mode)
Is directly influenced by the outdoor air temp.
What is the max. level that you should never exceed when filling a cylinder with refrigerant? (ambient = 70 F)
80%
To recover refrigerant is to?
Merely remove it from a system and store it in an approved cylinder
What is the RPM of an 8” pulley if the 3” drive pulley is spinning at 1720 RPM?
R1xS1=R2xS2
645
Considering the first law of thermodynamics, is it valid to say?
Heat - as a form of energy - cannot be created or destroyed
Atmospheric pressure has a direct influence on the boiling point of water?
1. True
2. False
- True
What type of copper tube is commonly used for air conditioning?
Type “L”
Nitrogen is?
1. The main substance in our atmosphere
2. Flammable
3. Toxic
4. All of the above
5. None of the above
- The main substance in our atmosphere
What corrective action should be taken when you discover a zone damper actuator motor is seized?
Replace the motor, reactivate and test the damper
If a water regulating valve for a condenser is jammed and too restrictive what happens to the compressor amperage?
2.Compressor amperage will rise
Hermetic compressor motors for residential air conditioning are generally?
PSC
