HVAC 2 Exam Review

Which of the following factors increases friction loss in a water pipe?

Increased water velocity

How many air temperature sensors does a dry-bulb economizer use?

One

The material commonly used for the under-floor loop in radiant floor heating systems is

PEX tubing with an oxygen barrier

If a heat pump works normally in the heating mode but will not provide cooling or defrost mode, which component is most likely defective?

Reversing valve

Why is a 24VAC common lead connected to a digital thermostat?

To power the thermostat

The variable-speed indoor fan motor receives low-voltage input signals by way of

a 16-pin connector

If the outdoor check valve sticks closed during the cooling cycle, there will be

a low suction pressure and high superheat at the indoor coil

The condensate from a condensing boiler is

acidic

In an electronic air cleaner, the output of the high-voltage power supply is applied to

both the collector and ionizer

An economizer uses mixed/discharge air sensor to control the open or closed position of

both the outdoor and return dampers

The enthalpy sensor(s) used with an economizer control

changeover from free cooling to mechanical cooling

When troubleshooting a problem suspected to be caused by a malfunctioning economizer damper, one of the first things to do is

check an operating damper for defects and binding

Signs of high relative humidity include

condensation on windows

Defrost is initiated by the

defrost control

A two-pipe system in which supply and return water flow in opposite directions is called a

direct-return system

When a humidifier experiences water overflow, the problem is often caused by a

dirty float valve

A three way zone valve located at the inlet of a heating terminal acts as a

diverting valve

During dual-fuel heart pump operation, the compressor and furnace burner can operate together

during periods of defrost

In an economizer that uses differential enthalpy sensing, what type of air does the economizer control module select for cooling

either outside or return

In the cooling mode, the reversing valve is normally

energized

Air-to-air heat pumps produce heat by

extracting heat from the outdoor air and transferring it to the indoor air

If a humidifier is not running, the problem is usually caused by a

faulty control circuit

A boiler installed in a rural area is most likely to be fueled by

fuel oil

In addition to the reversing valve, the other major difference between a heat pump and a cooling-only system is that

heat pumps require two metering devices

The function of a reversing valve will be affected by all of the following EXCEPT

high superheat settings

Some humidifiers are controlled by

humidistat

A Belimo Pressure Independent Characterized Control Valve is a practical choice

in commercial hydronic systems with variable-speed pumps

When a heat pump is operating in the heating mode, the refrigerant bypasses the

indoor coil metering device

Pressure drop in a hydronic heating system is caused by

internal friction

The purpose of shutoff valves installed on both sides of a circulator pump is to

isolate the pump for repairs

If the outdoor thermostat is not closed and this system is in the heating mode, a likely symptom would be

less supplemental heat available

Water at different temperatures within a hydrating system will

migrate

A tight building is characterized by the

presence of tight windows

Differential-pressure gauges are commonly referred as

readout meters

A device that uses a heat exchanger to transfer heat from warmed indoor air to ventilation air entering a building is a

recovery ventilator

Low primary voltage at the control circuit transformer may cause

relay chatter

The heat pump component that is controlled through room thermostat terminal O is the

reversing valve

If a heat pump will not initiate defrost and you suspect the reversing valve, the quickest way to verify your suspicion is to

see if the reversing valve switches when the operating mode is changed

A one-pipe system has a continuous run of pipe from the supply connection to the return connection is called a

series-loop system

The first thing that must be determined before selecting a circulating pump is the

system flow rate in gpm

If a heat pump blows cool air into the conditioned space during the colder parts of the heating season, a possible cause is

that the supplemental electric heaters are not on during defrost

Which of the following actions is most likely to occur first when a zone thermostat calls for heat

the circulator pump starts

Which of the following conditions is not common and proper during the defrost mode?

the compressor shuts off

In the reverse-cycle heating mode

the indoor coil acts as a condenser

What happens in the cooling mode if the discharge temperature switch fails?

the outdoor fan does not run

Which of the following is true of a pilot-operated valve?

the solenoid coil operates a plunger which opens a smaller valve port

Energy recover ventilators are more likely to be found

throughout the united states

A slow-opening zone control valve helps prevent

water hammer

One possible cause of a low humidity complaint would be

water supply feed valve closed

When an electronic air cleaner is operated at an airflow above that recommended by the manufacturer, the filter's cleaning ability is

worse