FREE Air Conditioning Repair Airflow and Duct Systems Questions and Answers

Question 1

A technician measures the Total External Static Pressure (TESP) on a residential furnace and gets a reading of 0.9 inches of water column (IWC).
The manufacturer's data plate specifies a maximum TESP of 0.5 IWC.
What is the most likely consequence of this reading?

Accepted Answer

Reduced airflow may cause the evaporator coil to freeze or the heat exchanger to trip on high limit.

Answer

The blower motor will consume less amperage due to a reduced workload.

Answer

System efficiency will increase because the air is moving more slowly.

Answer

The system will provide better dehumidification in cooling mode.

Question 2

In a rectangular sheet metal duct system, what is the primary purpose of installing turning vanes inside a sharp 90-degree elbow?

Accepted Answer

To reduce air turbulence and minimize static pressure loss.

Answer

To increase the velocity of the air around the bend.

Answer

To filter large debris from the airstream before a transition.

Answer

To intentionally create back-pressure for air balancing.

Question 3

A technician confirms proper blower motor operation but measures significantly low airflow moving through the residential air handler. Which of the following is the most common and likely cause for this issue?

Accepted Answer

A dirty or overly restrictive air filter.

Answer

An oversized return air plenum.

Answer

Leaking supply ducts in the conditioned space.

Answer

A thermostat that is improperly calibrated.

Question 4

A customer complains of a loud "banging" or "popping" noise from their rectangular metal ductwork shortly after the blower motor starts and stops. What is the most probable cause of this noise?

Accepted Answer

Undersized or inadequately supported ductwork experiencing "oil canning."

Answer

The use of flexible duct connectors at the plenums.

Answer

Debris such as a loose screw rattling inside the duct.

Answer

Excessive air velocity causing the registers to vibrate.

Question 5

To get an accurate measurement of a system's Total External Static Pressure (TESP), where should the two test probes of a manometer be placed?

Accepted Answer

In the supply plenum after the indoor coil and in the return plenum after the filter but before the blower.

Answer

In the return grille and in the furthest supply register.

Answer

Immediately before the blower wheel and immediately after the blower wheel.

Answer

In the supply plenum after the indoor coil and in the return plenum before the filter.

Question 6

When comparing two duct runs of the same diameter and length, which of the following will result in the highest friction loss and the greatest reduction in airflow?

Accepted Answer

An undersized, flexible duct with several sharp bends and sagging sections.

Answer

A straight run of smooth, rigid metal duct.

Answer

A properly sized, rigid metal duct with two 45-degree elbows.

Answer

A properly stretched, flexible duct with one gradual 90-degree bend.