HVAC 111 CHAP 7 EXAM PREP
1,2
A 120 VA step-up transformer with 100 V primary and 200 V secondary will have a primary current of ______________________________ A.
0.6 A
A 120 VA step-up transformer with 100 V primary and 200 V secondary will have a secondary current of ____.A. 0.6.
2
A 40 VA transformer with 120 V primary and 20 V secondary will have a limiting secondary current of ______________________________ A.
False
A normally closed (NC) contact on a relay closes when the coil is energized.
False
A step-up transformer produces a higher primary voltage than the secondary voltage.
laminated
A(n) ______________________________ core is made of thin iron sheets that are riveted or glued together.
Winding
Coil of wire used in a transformer
True
Contactors are heavy-duty devices.
Coil
Current-carrying wire designed to produce an effective magnetic field
False
Direct current supplied to an electromagnet causes the magnetic poles to alternate location.
Relay
Electrically operated switch controlled by an external signal
False
Excessive supply voltage to the relay and contactor coils is a common cause of chattering.
Resistive load
Heating element commonly used for refrigeration evaporator defrost
False
Holding current is drawn by a solenoid coil when it is first energized.
3 V
If the turns ratio in a transformer is 3:1, and the voltage in the primary coil is 9 V, the voltage in the secondary coil will be ____.
False
Inductive reactance occurs when direct current is applied to coils.
Inductive load
Load made of coils of wire and powered by alternating current
Solenoid
Mainly used in HVACR to open or close a valve to control fluid flow
Armature
Movable plate that may be hinged or slide along a fixed track in an electromagnetic device
True
The back emf in a dc-powered coil can be greater than the supplied emf.
solenoid valves
The configurations shown in this diagram are typically used for ____.
True
The more turns of wire around the core of an electromagnet, the stronger the magnetic field will be.
apparent power
The volt-ampere rating is the ____ rating of a transformer.
Solenoid Parts
This image provides an exploded view of a(n) ______________________________.
resistor
To prevent back emf from arcing in a dc-powered coil, a(n) ______________________________ can be added in parallel to the coil.
False
Transformers work with direct current.
Transformer
Uses coils of wire to produce magnetic fields and transfer ac from one coil to another
The coil is shorted and should not be powered up.
What does it mean if you check a solenoid coil with an ohmmeter and it reads zero?
Providing a counterforce
What is the purpose of the spring in this diagram?
The coil will draw more current.
What will happen if the plunger in a solenoid cannot retract into the core?
secondary voltage
When checking a transformer in a live circuit, the first step is to check the ____.
The electromagnet remains magnetized when the coil is de-energized.
Which statement about electromagnets is false?
The temperature rating indicates the amount of heat the coil will produce when energized.
Which statement about solenoid coils is false?
replace the entire circuit board
f a relay soldered to a circuit board fails, you must ____.
