System Controls and Schematics Flashcards
What are the 5 parts of a relay?
Coil, core, return spring, armature, and contacts
What are the 4 most common arrangements for the contacts of a relay?
SPST-NO (single pole, normally open), SPST-NC (single pole, normally closed), SPDT, (single pole, double throw) and DPDT (Double pole, double throw)
What are the 2 most common capacitors used in HVAC systems?
Run capacitor and start capacitor
What is the material called that is used to separate the two plates in a capacitor?
Dielectric
What activates the pressure switch?
The inducer motor
What is flame rectification?
AC electrical current that sends a very small current from the CPU to the flame rod.
Where is the CPU located?
The electronic control board
In a cooling unit, where is the high pressure switch located?
In the tubing between the discharge side of the compressor and the condenser coil.
What is the function of the low pressure switch?
It monitors the refrigeration system for a loss of refrigeration charge.
What is a relay?
Is an automatic remote control device that uses one or more initiating devices such as a switch, to operate or control another device connected either in the same circuit or in another circuit.
A relay in a schematic is always shown in the ____ state and the contacts are said to be in their normal positions.
De-energized
Describe a relay coil?
A conductor formed into loops in such a way that, when current flows through the coil, an electromagnetic field is created.
Describe core?
A core is made of magnetic material. It is magnetized from the polarity of the magnetic field created by the energized coil.
Describe the return spring?
When the coil is de-energized, this spring returns the armature to its normal position.
Describe armature?
This is a moveable metal strip that provides the mechanical action to operate the moveable contacts connected to it.
Describe normally open contacts?
This is an open set of contacts; these are in the open position when the relay coil is not energized.
Describe normally closed contacts?
This is a closed set of contacts; these are in the closed position when the relay coil is not energized.
What are SPST and DPST relays used for?
Switching equipment on and off
Describe time delay on energization?
When contacts change only after a specific time
Describe delay on de-energization?
When the contacts change instantly when a relay is energized
What is a capacitor used for?
To increase the running efficiency of the motor or to give it an initial boost in torque at start up.
What is capacitance?
The ability of an electrical device to oppose any change in voltage across that device.
The insulating material in a capacitor is known as what?
Dielectric
Changing the dielectric material also changes the capacitance. True or False?
True
