What is the function of a transformer in a gas furnace?
It reduces line voltage to control voltage.
On a call for heat, the thermostat energizes the __________ terminal
W
What is the function of the inducer in a gas furnace?
It brings in air for combustion
Rollout limit switches are located in the __________.
Burner area
Which of the following statements is true regarding inshot burners?
They require a seperate flame carryover channel.
A furnace with an AFUE of 90% or higher has ___________.
Both primary and secondary heat exchangers.
For natural gas applications, an ideal line pressure is __________
7.0 in. w.g.
For natural gas applications, the manifold pressure typically is set at _____________.
3.5 in. wg.
In a gas furnace application, "ESP" refers to the ___________.
resistance to air flow in the supply and return ducts
What is the first step in the sequence of operation for a typical gas ignition system?
The thermostat closes the R-W circuit
In a counterflow furnace, air passes from ___________.
The top to the bottom of the furnace
Regarding combustion air requirements, a "confined space" is defined as a space who's volume is ___________ per 1,000 BTUH of the combined input rating of all appliances installed in that space.
Less than 50 ft.^3
Oil furnaces are vented with _________ venting material.
Type L
The purpose of a CAD cell in an oil furnace is to _______________.
Prove the presence of flame
Normal CAD cell resistance is ______________ with flame present.
Less than 1,600 Ohms
Oil furnaces typically are designed to burn _____________.
#2 fuel oil only
Why is it necessary to bleed fuel lines prior to burner operation?
To remove air bubbles.
What tools are used to adjust an oil burner?
CO2 analyzer and smoke gun.
A properly adjusted oil burner should have a smoke test reading of _________.
0
Net stack temperature should be within the range of _____________
400 to 500 *F
If the measured temperature rise is ___________ than the range shown on the furnace rating plate, you should __________ the blower speed.
Higher, increase
Air flow should be as close as possible to _________ per ton of air conditioning.
400 CFM
The compressor changes refrigerant from a ________ to a _________.
Low-pressure vapor, high-pressure vapor
In the condenser, refrigerant is changed from a _________ to a _________.
High-pressure vapor, high-pressure liquid
The purpose of a metering device is to __________.
Create a pressure drop
A system that uses a TEV as a metering device _____________.
Must be charged by the subcooling method
What is the state of the refrigerant leaving the evaporator?
Low-pressure vapor
When you use the superheat method of verifying a system's refrigerant charge, adding refrigerant should ____________.
Increase suction pressure and decrease suction temperature
When you use the subcooling method of verifying a system's refrigerant charge, what should you do if the measured subcooling is more than 3 *F lower than the recommended subcooling value?
Add refrigerant in the vapor state.
Many "no cooling" calls are due to ________.
Neglected air filters
What type of refrigerant oil must be used with R-410A?
POE
Which thermostat terminal controls the reversing valve if the manufacturer energizes the reversing valve in the heating mode.
B terminal
Terminal "R" on a thermostat is used for ____________
24-V ac input
Thermostats that have W2 and/ or T2 terminals are known as ____________
Multistage
In general, the "O" terminal on a heat pump thermostat is energized whenever the system selector switch is set to _______
Cool
The purpose of a heat anticipator is to __________
prevent wide swings in room temperature.
A bimetallic strip is a(n) _________ control
Electromechanical
Fossil-fuel kits often are used in ____________ systems
Heat pump
Low-ambient controls are used to ______________.
Maintain high-side pressure when the outdoor temperature is low
A bypass damper is a component of a(n) ____________ system
Zoning
Enthrall controllers measure ________________.
Both dry-bulb temperature and humidity
PTC and NTC thermistors are often used as ____________.
Sensors
For rectangular sheet metal ducts, the usual duct depth is ____________.
8 in.
Which duct system component connects a stack to a horizontal duct at a lower level?
Boot
Which duct system component delivers air to a register box?
Branch duct
A standard elbow has a curve ratio of ___________.
0.5
Take-offs should be placed at least ________ duct diameters or elbow widths downstream from an elbow.
7 1/2
A fire damper is activated with a ___________.
Fusible link
For heating application, local air velocities generally are ____________.
Less than 40 ft/min
The distance traveled by an airstream between leaving the discharge outlet and the point at which its velocity falls below some specified terminal level is called the __________.
Throw
How many air changes per hour are required to prevent the formation of stagnant regions of air?
8 to 10
For cooling operation, what is the ideal location for a return intake?
Near the ceiling
Lengths of round duct may be joined by using any of the following except _______________.
Drive clips
The radius of a flexible duct bend must not be less than the ________ of the duct.
Diameter
When run horizontally, flexible duct must be supported at maximum intervals of _____________.
5 ft.
When run vertically, flexible duct must be supported every __________.
6 ft.
Flexible duct sag should be limited to _______ per linear foot between supports.
1/2 in.
Which of the following is not approved for sealing duct board?
Duct tape
What technology provides for multiple temperature-controlled areas within a structure?
Zoning
The exchange of indoor air for outdoor air is known as ____________
Ventilating
Which of the following devices can provide "free cooling" when outdoor conditions permit?
Air-side economizer
A differential enthalpy controller measures _____________.
Both dry-bulb and wet-bulb temperatures
In a forced-air system, static pressure is a force that ____________.
Pushes against the walls of a duct from inside the duct.
Gauge pressure plus atmospheric pressure equals _________ pressure
Absolute
In a forced-air system, velocity pressure is the ________________.
Difference between the total pressure and the static pressure.
The process of measuring velocity pressure at several locations across a cross section of duct is knows as making _____________ reading.
Traverse
Which of the following test instruments provides direct readings in feet per minute?
Anemometer
In any duct system, when the velocity of air is _______, the resistance to air flow is _______________.
Increased, increased
Which of the following is not a factor in determining proper duct size?
Temperature difference
In a duct system, the angle between the sides of a transformation piece (from larger to smaller must be less than _____________.
60*
Which equation is used to calculate the rpm of a belt-driven fan?
Motor pully diameter X motor rpm / fan pulley diameter
What is the synchronous speed of an AC induction motor that has six poles and operates with a 60-Hz power supply?
1,200 rpm
The CFM of a fan is ________ the rpm of the fan.
Directly proportional to
Static pressure is ____________ the rpm of the fan.
Proportional to the square of
The efficiency of a fan is defined as its ____________ divided by its __________
Power output, power input
Humidity often needs to be added to the conditioned air in the __________ mode.
Heating
Humidity often needs to be removed from the conditioned air in the _______________ mode.
Cooling
The external static pressure (ESP) of a system is measured in __________
In. w.g.
Depending on the manufacturer, a heat pump application that requires 6 ton of cooling will have a total system air flow requirement of approximately ________________ CFM.
2,700 to 3,000 cfm
In high latent heat applications, how should the fan speed be adjusted to increase dehumidification?
Fan speed should be decreased.
In high sensible heat application, how should the air flow rate be adjusted to avoid unwanted dehumidification?
Air flow rate should be increased.
In a balanced air distribution system, the total supply CFM should be __________ the total return CFM.
Within +- 10% of
A common recommended air flow for residential cooling applications is __________ per ton of cooling.
400 cfm
What effect does reducing the cooling blower speed have on the temperature drop across the evaporator coil?
The temperature drops will increase.
Excessive humidity in the conditioned space may indicate that the _________________.
Blower speed is set too high
What effect does high ESP have in the heating mode?
Higher-than-normal temperature rise.
ESP often is measured with a(n) _______________.
Magnehelic gauge
What is the first step in investigating a "noisy equipment" complaint?
Gather as much information as possible from the customer.