313D Practice Exam 1 (Complete) Flashcards by Handy Bros Academy .

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

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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

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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

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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

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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

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What is the air velocity if a pitot tube connected to an inclined manometer gauge reads 0.2” water column?

1791 fpm

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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

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When testing a compressor motor winding with a megger, what reading would indicate a good, clean system?

100 megaohms

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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)

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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

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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

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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

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What is an indication of a plugged metering device?

Low suction pressures
High superheats
Low head pressures
High subcooling
Low amp draws

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When constructing a walk-in freezer box, where should the vapour barrier be installed?

Outside on the warmest side

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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

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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

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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.)

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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.)

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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

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Concerning hermetic compressors, when does the compressor draw from the evaporator?

Mostly during the suction stroke

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Potential relay contacts are closed by?

The loss of counter EMF

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If a system has a “non-bleed” type TXV, what should be installed?

A hard start kit

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Power loss in a motor is converted to heat energy?
1. True
2. False

True

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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

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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? 1. 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 2. Both wires to the line side of the contactor 3. Both wires to the load side of the contactor 4. 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

4. 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

1. 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?

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

1. 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

1. 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

1. 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