Air Conditioning Repair Airflow and Duct Systems Questions and Answers

Question 1

A technician measures the total external static pressure (TESP) on a residential air handler and finds it to be 1.1 inches of water column (in. w.c.).
The manufacturer's data plate specifies a maximum TESP of 0.5 in. w.c.
Which of the following is the MOST likely consequence of this condition?

Accepted Answer

Reduced volumetric airflow (CFM) leading to poor system performance.

Answer

Increased refrigerant subcooling at the condenser.

Answer

The system will deliver more conditioned air than designed.

Answer

Over-amping and premature failure of the condenser fan motor.

Question 2

What is the primary purpose of the return air grille in a forced-air HVAC system?

Accepted Answer

To cover the return duct opening and, in many cases, hold the air filter.

Answer

To mix conditioned air with room air for better circulation.

Answer

To control the velocity of the air leaving the supply duct.

Answer

To prevent the buildup of positive pressure within the conditioned space.

Question 3

Which of the following is the most common cause of reduced airflow across the evaporator coil in a residential air conditioning system?

Accepted Answer

A dirty or clogged air filter.

Answer

An oversized return duct.

Answer

A refrigerant undercharge.

Answer

A malfunctioning thermostat.

Question 4

A homeowner reports a high-pitched whistling sound coming from the supply registers, which becomes more noticeable when some vents are closed. What is the most likely cause of this noise?

Accepted Answer

Excessive air velocity due to restricted outlets.

Answer

The blower motor bearings are failing.

Answer

A loose panel on the air handler cabinet is vibrating.

Answer

The ductwork is undersized for the system's airflow.

Question 5

In rectangular duct design and fabrication, what does the term "aspect ratio" describe?

Accepted Answer

The ratio of the long side of the duct to the short side of the duct.

Answer

The ratio of the duct's total length to its total number of fittings.

Answer

The percentage of airflow lost due to friction within the duct.

Answer

The relationship between the supply air temperature and the return air temperature.

Question 6

A technician needs to measure the velocity of the air, in feet per minute (FPM), moving through a duct. Which of the following instruments is specifically designed for this purpose?

Accepted Answer

An anemometer.

Answer

A psychrometer.

Answer

A manometer.

Answer

A micron gauge.