HVAC ELECTRICAL MAIN TEST
In the schematic, what voltage would be found from terminal Y to the input side of the coil online #11?
0 Volts
in the schematic, what voltage would be found from terminal G to the load side of the transformer
0 Volts
In the schematic, What voltage would be found across the fuse in the line #10 with the thermostat closed?
0 volts
which of the following is equal to 100 milliamps?
0.10 Amperes
Three 300 ohm resistors are wired in parallel. The total resistance equals;
100 ohms
In the schematic, if the fuse in L2 is blown the:
Blower motor will continue to operate
In the schematic, what voltage would be found across the contacts when energized in line #8?
0 Volts
How many Watts of power are used by a heater operating at 240 Volts and drawing 5 amps?
1200 watts
The synchronist speed of 4 Pole, 60 Hz single phase motor is;
1800 RPM
Which of the following is equal to 2.1 KW
2,100 Watts
The voltage to ground of a "high leg" or "Stinger Leg" on a three phase open Delta system will be approximately;
208
In the schematic, what voltage would be found from terminal Y to the output side of the coil online #11?
24 Volts
In the schematic, what voltage would be found across L1 to L2?
240
in the schematic, what voltage would be found across the condenser fan motor?
240
Utility companies usually supply residential homes with ___________ service.
240V, single phase, three wire
Relay's are generally used to control inductive loads up to _______________ amps.
25
Three defrost heaters, each 15 ohms are wired in parallel to a 120 volt power supply. How many watts of power will be used?
2880 Watts
What is the minimum number of wires required between two Start/Stop push button controls?
3
Which of the following is an acceptable temporary replacement for a run capacitor rated at 35MFD@440VAC;
37.5MFD @ 440VAC
Which of the following is generally considered to be within the maximum allowable (plus or minus) supply voltage variation?
5%
A parallel circuit contains 18 ohms and a 9 ohms resistor. The total resistance equals;
6 ohms
How much resistance must be placed in a 120 Volt circuit in order to limit the current to 2 amps?
60 Ohms
A parallel circuit consists of three resistors. R1 = 30 ohms R2 = 15 ohms R3 = 10 ohms if the current through R2 = 4 amperes, what is the source voltage?
60 Volts
A transformer has a 1000 turns of wire in the primary coil and 500 turns in the secondary coil. if 120 Volts are applied, the output voltage will be;
60 Volts
One horsepower is equal to ________________ Watts
746 Watts
An ohmmeter should never be connected to;
A charged capacitor until it has been discharged
Any material that will readily release electrons is called
A conductor
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and the condenser fan motors are shortcycling. The blower motor is not running. This could be caused by;
A faulty blower motor or blower relay
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan motors are short cycling. The blower motor is not running. When the fan switch at the thermostat is moved from the AUTO position to the FAN ON position, the blower runs. This could be caused by;
A faulty thermostat - AUTO / FAN ON switch.
When checking the windings of a 3 phase motor
All 3 terminals should show the same resistance
In the schematic, the coil on line #12 controls the;
Blower Motor Relay
To change direction of rotation of a three phase motor;
Change the position of any two supply wires.
The starting device usually used on a single phase, fractional horsepower motors requiring low starting torque is the
Current Relay
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will;
Decrease
Resistance can be calculated by
E divided by I
Which of the following motors is most energy efficient
ECM ( Electronically Commutated Motors )
Which of the following would be considered an inductive load?
Electric Motor
A solenoid valve coil operates on the principal of;
Electromagnetism
Direct Digital Control (DDC) is
Electronic controls use for equipment operation and monitor
A typical thermocouple used on a gas furnace can;
Generate a small DC electrical current
With a motor running at full load, voltmeter leads are placed on L1. and T1 terminals of the contactor. The voltmeter indicates no measurable voltage. This is an indication of;
Good clean contacts
The safety ground conductor is usually color coded
Green and bare.
An Electron has
Has a negative charge
The capacitor start-capacitor run (CSRC) motor provides;
High starting and running torque.
The symbol for Current is
I
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will
Increase
The total resistance of a parallel circuit will be;
Less than the smallest resistance
A device with overload protection used to control motor is a;
Line starter
What connects to the terminals T1, T2, & T3 on a contactor or motor starter?
Load connections
When testing a capacitor with an analog or digital ohmmeter, the meter should;
Measure low resistance then return to high reading
Capacitors are rated in?
Microfarards & Volts
Single phase motor speed is determined by the;
Number of stater Poles
Which meter is used to bench check a motor for shorts or open windings?
Ohmmeter
Which of the following meters must use its internal power to check a load or circuit
Ohmmeter
what would be the result, if a 24 volts , 20-ohm low voltage contactor coil were wired in series with a 24 volt, 200-Ohm control relay coil?
Only the control relay would operate.
Impedance is?
Opposition to alternating currentflow.
The ___________ drawing illustrates where the components are located in small appliances.
Pictorial
A transducer can create a signal based on;
Pressure
An electronically commutated motor (ECM) is designed to ;
Provide proper air flow under various conditions.
Voltage can be calculated by
R divided by I
Like Charges?
Repel each other
If contacts become badly pitted, it is acceptable to;
Replace the contacts or control
On a good single-phase compressor motor, which winding terminals have the highest resistance?
Run to start.
What is a term used to describe the output side of a transformer?
Secondary side
Excessive current can be caused by;
Short circuit
Which of the following material would be best suited for use as a semiconductor?
Silicone
When troubleshooting the AC system in the schematic, the following conditions are found. The authorities that contacts are closed the compressor and condenser fan are not running the blower motor is running. This could be caused by;
The HP, LP, overloads, or oil pressure switch are open (line #11).
In the schematic, the coil on line #11 does not control
The blower motor
When testing the winnings of a single phase motor
The common to run terminals show the lowest resistance
Direction of rotation of a single phase induction motor is determined by;
The direction of current flow through the start winding
current flow is?
The flow of electrons in the circuit.
When resistors are wired in Parallel
The voltage drop across each resistor Will depend on the value of each resistor
A three phase load requires a minimum of;
Three supply lines
On an electronic oil safety switch what changes the pressure signal to electrical signal?
Transducer
Is True or False; Current flow will decrease when voltage increases
True
To discharge a capacitor prior to ohmmeter testing;
Use a 15,000 or 20,000 ohm, 2 to 5 watt resistor across the terminals
Transformers are rated according to
VA at the secondary
A step up transformer increases
Voltage
Fuses are sized by:
Volts & Amps
Which of the following is the correct formula for determining wattage in an electrical circuit?
W = E x I
The electric meter on a house measures the ______________ passing through it.
Wattage
In the schematic, the crank case heater will operate;
When the compressor is off.
Which of the following is the symbol for impedance in an AC circuit?
Z
When current flows in a 2 wire circuit (such as 120 Volts) if a clamp on amp meter is clamped around both wires. What measurement would you expect?
Zero amps due to cancelation of the two fields.
In a series circuit, the voltage drop across each resistance (load) will;
add up to equal the source voltage.
Contactors are rated according to the maximum amperage through the;
contacts
A diode is used to
control the direction of electron flow
When testing a motor with an ohmmeter, the following measurements are recorded, common to run 4 ohms, common to start 6.2 ohms, run to start 10.2 ohms, and common to ground 20.4; this indicates a/an;
grounded condition
Capacitors are always connected to the start winding
in series
If the conductor in an AC circuit is wound into a coil, the resulting EMF opposes the supply voltage. This opposition is called
inductive reactance
The thermal overload contacts on A-line starter are usually _____________ reset
manual
Resistance is
opposition to current flow
Circuit breakers & fuses are primarily used to provide;
protection from an overload of current
A capacitor analyzer is designed to read;
the capacitance of a capacitor
In an electrical wiring, a black colored wire in an alternating current circuit usually indicates;
the hot conductor