Hvac Vocabulary Flashcards
Hvac
A fast acting fuse is commonly used on motor with a high starting current.
False
A flat bimetal strip deforms or bends as temperatures rises because the copper expands more than the steel.
True
After a ptc relay increase its resistance, the motor current seeks the path of least resistance, which is through the run capacitor.
True
A low pressure safety control is set to maintain a specific evaporator temperature
False
A low pressure safety control is set to shut down the compressor in the event of refrigerant loss
True
An above atmospheric pressure element is used to control heating units
False
An internal bimetal protection device will open the motor circuit when the temperature reaches 200 f to 250 f
True
An oil pressure motor control connected to a compressor’s lubrication system shuts off the compressor if the oil pressure drops to low side pressure
True
Any standard relay may be used to replace a lockout relay.
False
A picture relay has a low resistance when motor circuit is first energize, so it is easier for the current to pass through the PTC relay than through the run capacitor.
True
A time delay fuse may allow a motor to be damaged from high current before the time delay is over.
True
Bimetal discs are often used for last snap-action applications.
True
Current limiting fuses use temperature sensitive resistors that close the motor circuit as temperature rises.
False
External bimetal protection devices only open a motor circuit if the current is too high.
True
If a thermistor resistance increases as temperature increases, the thermistor has a negative temperature coefficient (NTC).
False
If the contact points of a thermostatic motor control were to open very slowly, electric arcing could burn the contacts.
True
In order for a PTC relay’s resistance to drop low enough for a motor to start again, it must have enough time to cool down.
True
The fuses for a motor in an HVACR system are usually factory installed within the compressor dome.
False
The vertical lines in a ladder diagram identify the controls and loads located in a circuit.
False
Three phase motors may use the same starting relays that single phase motor use.
False
When the pressure inside an above atmospheric pressure elements increase, it closes a electrical circuit.
True
When the thermistor in a PTC relay has high resistance, it acts as a close switch or contact.
False
Copper conducts heat better than glass.
True
During a state change, the temperature of the substance always change.
False
The sun heats the earth through conduction
False
During operation, the compressor motor will rotate in the opposite direction to change the direction of refrigerant flow.
False
In a split phase motor, the run winding has the greatest amount of resistance.
False
The contacts of a potential relay are normally open.
False
A shade pole motor has a high starting torque
False
The human body has resistance.
True
The starting winding is wound with finer wire than the running winding so it has great resistance.
True
The start capacitor is connected in series with the starting winding.
True
The voltage draw is more when the motor is starting than when it is running.
True
Most thermostat in the HVAC industry are 120 volts.
False
Digital thermostats usually display temperature, time of day, programming and operating status.
True
Single phase motor are more efficient than three phase motor.
False
If contact become dirty or pitted, it is acceptable to sand or file them as a permanent repair.
False
When testing a motor with a ohmmeter, one winding show a 1000 ohm continuity to motor frame. This is an indication of a good safety ground.
False
A 240 volt, 3 wire circuit can be split into two 120 volt circuits.
True
