03314 Control Circuit and Motor Troubleshooting: Module 2
Thermistors are widely used to sense temperatures in HVAC systems because they are very_?
Versatile
A characteristic of some combination fan/limit switches is_?
The ability to function in circuits of different voltages
Which type of motor breaking is often used with AC motors being controlled by a VFD?
Dynamic
A VFD control panel is typically_?
Removable
Why is 24V used in control circuits?
Components are easier to install and service
On a single-phase compressor motor, the lowest resistance will be measured across terminals_?
C and R
Across which indoor-unit terminals should a meter be used to check indoor fan operation?
C to G
Installers should use a heavier gauge thermostat wire if the wire length exceeds_?
100'
ECM's should be replaced if their motor winding resistance to ground is less than_?
100,000 ohms
Adding a PTC thermistor can increase the starting torque of the compressor by as much as_?
200-300%
The coil power supply for most relays used in HVACR control circuits is_?
24VAC
What is the maximum voltage permitted when using a motor rated for 208-240V?
264V
When a unit with several inductive loads initially starts (such as a compressor and condenser fan motor), how large a voltage drop would be expected without concern, due to the additional current draw that is related to starting inductive loads?
3%
How is a lockout relay in a control circuit reset_?
Interrupt control circuit power
What does the presence of a 4-pin communications connector on an ECM signify?
It is a newer version motor
A thermistor that increases its resistance as temperature rises is said to have a_?
Positive coefficient of resistance
Which of the following is not a perimeter that can be programmed or monitored when using a VFD?
Power factor
Which of the following is a benefit to derided from using a pulse width modulate (PWM) variable frequency drive (VFD) versus an analog SCR VFD?
Reduced problems with harmonics
Sequential energizing of an ECM's motor windings provide_?
Rotation of the rotor
Which of the following would not be a factor when setting up an air handler's capital ECM motor control to deliver the correct airflow in all operating modes?
Fuel gas heat content
Grounding wrist straps should be worn when_?
Handling solid-state devices
What is the purpose of the jumper on the 5 - pin connector on an ECM's motor control section?
Input Power Voltage Selection
* Please see Page 47, "Figure 51 Fuse Tests".* A voltmeter is being used as shown on an energized circuit to test the fuse on the right. If the fuse is open, what will the voltmeter read?
0V
Electronic programmable thermostat's regulate the length of a furnace burners on-time with a_?
Cycle-rate adjustment
When using a motor other than a NEMA Design A or B with a VFD, what added precaution must be taken?
Add special drive circuitry
Listening to the customer's complaint does not provide_?
All information needed to find the problem
All of the following are inductive loads found an HVAC equipment except?
Crankcase heaters
After being energized, what type of function could a typical relate with normally closed contacts directly perform?
De-energize a crankcase heater
A pneumatic controller that increases the pressure of its branch line, when air temperatures in the condition space goes up is called a_?
Direct acting thermostat
A 24VAC transformer has dual-voltage primary leads and is factory-connected to the higher voltage lead. In this situation, the installing technician should_?
Ensure the primary lead and supply voltage match
Starting motors are around five times max running. This is called?
Locked Rotor Amps (LRA)
A reset controller in a hydronic heating system is used to_?
Monitor outdoor temperature
Where in a system is a PTC start thermistor installed?
Parallel with the run capacitor
Bimetal elements in room thermostats are usually_?
Spiral-wound
A thermostat terminal labeled W2 controls_?
The second stage of heat
Why are two sets of contacts (one set normally open and one set normally closed) needed on an indoor fan relay?
To ensure only one motor speed winding is energized at a time
