Study Guide 14 & 15

High pressure contacts are normally _____ type.
While checking a simple series 115-V circuit containing a fuse, a switch, and a light bulb, the technician's voltmeter reads 115 volts across the light bulb socket. The light bulb is not on. He correctly concludes that the _____ is defective.
light bulb
Low pressure control contacts are normally _____ type.
The fan relay, cooling relay, and heat relay are all _____ devices.
power control
Electrical controls are divided into two categories: _____ and _____.
power consuming; power passing
Non-power-consuming, or power-passing, devices are commonly referred to as _____.
The heater that functions in a thermostat in the heating mode is called the _____.
heat anticipator
The heater that functions in a thermostat in the cooling mode is called the _____.
cooling anticipator
The term used to describe when the temperature of a heated room rises above the thermostat's set point is called _____.
system overshoot
The term used to describe when the temperature of a heated room falls below the thermostat's set point is called _____.
system lag
The three separate power-consuming circuits in the low-voltage control of a typical heating and cooling fan unit are the _____, _____, and _____.
heat circuit; cool circuit; fan circuit
An oil failure control will allow a compressor to operate without oil pressure for _____ seconds.
up to 90 sec.
In a residential air conditioning system, how are the outdoor fan and compressor wired with respect to each other?
How does a thermistor motor overload device protect an electric motor?
It cuts out on overheat. It opens on high temp/overheat.
Explain how to read very low currents in a control circuit using a clamp-on amp meter.
Set meter to milliamps. (verify)
When applying a voltmeter to measure the voltage of a power source, on what range is the meter set?
You want to set it at a higher range then the supply voltage or the top range of the meter.
Where is the thermistor motor overload device usually positioned?
Generally embedded in the motor windings
In a high voltage circuit, is the fan motor a power-passing or power consuming device?
What are the three components that have to operate when a residential air conditioning system is in the cooling mode?
Indoor fan, outdoor fan & compressor
How is the cooling anticipator normally wired to the cooling contacts?
In parallel
List four reasons why low voltage controls are usually found on residential air conditioning systems?
Economical, safe, precise control, and technician does not need license
An oil pressure safety control usually has a 90-second time delay built into it. Why?
Allows time for the parallel pressure contact to mate. If the parallel circuit does not mate then the system will drop off on low oil pressure.
How is the heat anticipator normally wired to the heating contacts?
In series
What is the amperage capacity of a 240-V/24-V control transformer with a 40 V A rating?
1.66 amps (formula is in the book p. 297)
What device may be used to ensure that air is flowing through a duct before an electric strip heater is energized?
Sail switch