Troubleshooting Final Review

An R-22 system operating with a liquid pressure of 226 psig (110° saturation temperature). The specified system subcooling is 5°F. The liquid line temperature should be

105 degrees F

Which of the following measures is the standard airflow across an air-conditioning coil?

400 cfm per ton

An air conditioning system charged with R-410A is operating with a suction pressure of 130 psig which equates to a 45°F saturation temperature. If the manufacturer calls for a 15°F superheat, what should the suction line temperature be?

45°F + 15°F = 60°F suction line temperature

The compressor in an existing split system is being replaced. The system has a 35 foot line set. The factory charge for the condensing unit is 80 ounces. The installation instructions state that the factory charge assumes a line length of 15 feet and gives the per foot adjustment as 0.6 ounces per foot. How much refrigerant should be added to the system after the system has been evacuated?

80 ounces + ((35-15) x 0.6) = 92 ounces

The standard AHRI "A" design condition used for rating unitary air conditioning equipment is

95°F outdoor ambient temperature, 80°F dry bulb, 68°F wet bulb indoor temperature

For air conditioners, a rise in the return air wet bulb temperature causes

A decrease in the temperature difference across the evaporator coil

A system that is overcharged will operate with

A high subcooling and a low superheat

In general, a system that is overcharged will have

A high subcooling and a low superheat

A system with an inefficient compressor will operate with

A high suction pressure and a low head pressure

A fixed restriction system operating with a refrigerant undercharge will have

A high system superheat

A system that is undercharged will operate with

A low subcooling and a high superheat

In general, a system that is undercharged will have

A low subcooling and a high superheat

Organizations that support the TAB industry by developing standards and offering certification include

AABC, TABB, and NEBB

An air conditioner with a thermostatic expansion valve is operating with a condenser saturation temperature of 95°F and a liquid line temperature of 92°F. The factory specified subcooling for the current operating condition is 10°F. The technician should

Add charge because the system is undercharged

How does the refrigerant charge affect a system's subcooling?

Adding refrigerant increases the system subcooling

The amount of moisture in the air can be measured with

An electronic hygrometer

Why is testing and balancing an important part of HVACR residential systems?

Because HVACR systems are the largest energy appliances in a residence and energy costs have increased

What color should the flames be in a correctly adjusted gas burner?

Bright blue inner cone with darker outer cone

The velocity pressure of air moving through ductwork is measured

By subtracting static pressure from total pressure

The formula for measuring airflow using temperature rise is

CFM = Btuh ÷ (1.08 x Temperature Rise)

How can a technician check to see if the coil and condensing unit on an AC split system are matched?

Call the equipment supplier and provide the system model numbers

When changing a low voltage transformer, service technician should

Check all low voltage controls for shorts and grounds

When troubleshooting an induced draft gas furnace, what should be checked if the induced draft fan comes on but the igniter is never energized?

Check the draft pressure switch to see if it is closed

Before starting the unit:

Check the power supply with the unit off.

After replacing a blown fuse in a unit disconnect, the technician should

Check the system amp draw and compare it to the data plate rating

The first step in performing a TAB service on a system is

Collecting system specifications and equipment information

The reversing valve on most air source residential heat pumps is energized

During the cooling and the defrost cycles

The air filter should be checked

During the preliminary inspection

An anemometer is used to measure

Feet of air for air velocity calculations

When performing a test and balance procedures on a zoned system, correct airflow should first be established

For each zone before balancing the individual branches

Why should caution be exercised when replacing a low efficiency air filter with a higher efficiency air filter?

Higher efficiency filters have a higher pressure drop that can cause poor airflow.

The most important thing to know about a system before an operational check is:

How it should function

Instruments that can read the pressure in a duct system include

Inclined manometer, magnehelic gauge, and digital manometer

In general when a blower motor moves more air its amp draw will

Increase

How does scheduling maintenance save time and money?

It prevents small problems from becoming big ones.

How will an extremely dirty air filter affect the amp draw of a PSC centrifugal blower motor?

It will cause the motor current to decrease because the fan will be moving less air.

What should you do to isolate the root cause of the malfunction?

Perform tests to isolate the cause.

A common cause of low system superheat is:

Poor airflow across the evaporator

How is a temperature-pressure relief valve on a hot-water boiler tested?

Pull lever and look for water at outlet of discharge pipe.

The refrigerant condensing temperature for an air cooled system having a 20°F split is

RCT = 95°F + 20°F = 115°F

After any repair or part replacement, the most important thing you must do is:

Recheck the system to be sure the concern has been resolved.

An air conditioner with a fixed restriction metering device is operating with an evaporator saturation temperature of 40°F and a suction line temperature of 42°F. The factory specified superheat for the current operating condition is 12°F. After checking the airflow and determining that it is within specifications, the technician should

Recover charge because the system is overcharged

An air conditioner with a thermostatic expansion valve is operating with a condenser saturation temperature of 110°F and a liquid line temperature of 85°F. The factory specified subcooling for the current operating condition is 10°F. After verifying the condenser coil and airflow are good, the technician should

Recover charge because the system is overcharged

An air conditioner is operating with low system pressures, an evaporator saturation temperature of 20°F and a suction line temperature of 24°F. The suction line is frosting. The most likely cause of these symptoms is

Reduced airflow across the evaporator

How does performing planned maintenance save the customer money?

Reduced operational cost and longer equipment life

Adding a little extra refrigerant to a fixed metering system over the amount recommended by the manufacturer

Reduces both system capacity and efficiency

The phases of a planned maintenance service call are:

Routine maintenance, pre-start inspection, operational checks, and troubleshooting.

Which statement most accurately describes TAB?

TAB is used to conduct measurements and adjustments that are specific to testing and balancing, which are not normally performed in regular HVACR work.

What is the free area of a register or grille?

The amount of the grille face area that is open

How is a velometer used to determine the CFM at a supply register?

The average air velocity is multiplied by the free area of the register

The contactor on most residential split system condensing units controls

The compressor and the condenser fan motor

With the system operating, a technician gets a reading of 20 volts between the L1 and T1 terminals at the contacts of the contactor. This tells the technician that:

The contacts are defective because they have a measurable voltage drop.

A sling psychrometer can be used to determine the relative humidity by comparing

The dry bulb and wet bulb readings

The most reliable source of information on how to charge any particular piece of equipment is

The equipment manufacturer

When searching for the break in a circuit by hop scotching, the technician checks

The voltage at each switch in the circuit

A TAB technician determines that the total airflow entering the return grilles is much lower than the amount of air the blower is moving. This indicates that

There are leaks in the return side ductwork

A TAB technician determines that the total airflow leaving the supply registers is much lower than the amount of air the blower is moving. This indicates that

There are leaks in the supply side ductwork

The first step in troubleshooting a system is

To understand the system operational sequence

Before starting to change a belt on a belt drive blower, the technician should:

Turn the power to the unit off and lock it out.

A pitot tube is used to measure

Velocity pressure in ducts

The desired end result of performing a TAB service is to

Verify that the system is operating as designed

Can zeotropes be metered in the low side with the unit operating?

Yes, by slightly cracking open the low-side manifold valve and then closing it.

What type of refrigerant must leave the cylinder as a liquid to prevent the separation of the different components in refrigerant?

Zeotropic mixtures

A water source heat pump that trips the high pressure switch during the cooling cycle and the low pressure switch during the heating cycle may have

a fouled water coil

A fixed restriction system operating with a refrigerant overcharge will have

a low system superheat

A system operating with a high superheat and a high subcooling most likely has

a refrigerate restriction

How does system commisioning improve energy efficiency?

by insuring that the system is performing as designed

Most vapor charging is done with the compressor operating while charging is taking place; however, liquid charging

can be done either with the system off or operating.

The main advantage of measuring airflow using the temperature rise method is that temperature rise measurements

can be taken easily using a common thermometer

As an operational safety check, the equipment rooms for combustion appliances should be checked for high:

carbon monoxide levels

As an operational safety check, what should be checked in the combustion gases for combustion appliances?

carbon monoxide levels

As the outdoor ambient temperature increases with fixed metering, the required superheat

decreases

If some components are not functioning, and the system has line and control voltage, you should next

determine if the components are receiving voltage.

The most common times to perform a seasonal check on heating equipment is in the:

fall

The volume of air flowing out a supply register can be directly measured with a

flow hood

As the indoor wet-bulb temperature increases on fixed metering systems, the required superheat

increases

A problem that can look like refrigerant overcharge if a service technician is only looking at system pressures is

low condenser airflow

A problem that can look like low refrigerant charge if a service technician is only looking at system pressures is

low evaporator airflow

A dirty air filter would likely cause which of the following symptoms ?

low suction pressure

Why is planned maintenance often performed during the off-season?

most equipment fails during the off season

Technicians that use a systems approach to troubleshooting

must understand the inter-relationship between different system components

What kind of chart is required when calculating the liquid-line subcooling?

pressure-temperature chart

Two variables that have a great impact on the system performance of air conditioning systems are

return-air wet-bulb temperature and the airflow across the evaporator.

A tachometer is used to measure

rotational speed

When the liquid line is restricted, the supply of refrigerant to the metering device is reduced. What is the effect on suction pressure and superheat?

suction pressure goes down and superheat increases

TAB stands for

testing and balancing

When an evaporator float switch is used in the drain pan of an air conditioner or heat pump, if the drain pan fills up the float will interrupt the low voltage circuit to

the compressor contactor

The low pressure switch on a residential split system condensing unit normally interrupts the circuit to

the contactor coil

Before checking a system's operating superheat, the technician should first check

the evaporator airflow

A technician notes that an operating air conditioning system has ice formed on the suction line at the condensing unit. The technician can reasonably assume that:

the evaporator coil is also frozen over

Which manufacturer-supplied reference would probably be the most helpful on a no heat furnace in letting you know the pressure switch is open or failed to open?

the fault code reference list

In an induced draft gas furnace, the first component to energize on a call for heat is

the induced draft blower

Which manufacturer-supplied reference uses pass/fail tests to guide the technician to the possible cause of system malfunction?

the logic flowchart

What side of an air conditioning coil generally collects dirt?

the side where air enters the coil

The purpose of TAB is to document that

the system is performing as designed

The dampers on registers are normally not used for balancing the system airflow because

they will produce excessive noise in the space

Why must zeotropic refrigerant leave the cylinder as a liquid?

to avoid fractionation

Of the four phases listed below, which one is only performed on an "as needed" basis?

troubleshooting

Which of the following types of charge is usually employed when a partial charge is required?

vapor

Hopscotching is the technique that requires you to start at a point with correct voltage and then move one lead at a time until

voltage is lost.