NATE: AIR DISTRIBUTION TROUBLESHOOTING
QUESTIONS AND ANSWERS
An air conditioning service call is made and the complaint is that the system does not
seem to be cooling properly. It is noticed that the suction line and the evaporator coil are
frosted up. The filter is checked and it is clean. It is suspected that the indoor blower is
not operating at the proper speed. Technician A says that the speed can be verified with
a strobe tachometer to be sure that the rpms are as written on the nameplate.
Technician B says that the airflow can be measured by taking a static pressure reading.
Which technician is correct? - Answers- technician A
An airflow measurement taken in a duct system by drilling small holes in a vertical and
horizontal section of a rectangular duct to find an average air velocity reading is known
as: - Answers- a Pitot-tube traverse
To calculate velocity pressure when using a manometer, which of the following would be
the proper formula: - Answers- total pressure-static pressure= velocity pressure
What is the primary purpose of an isolation collar: - Answers- It is used to eliminate
furnace vibration through the duct system
Technician A measures the airflow in a main supply duct by using a Pitot-tube traverse.
His measurement is 1,200 fpm. The area of the duct at the point of measurement is 8" X
30". He says that he has 2,000 cfm. Technician B measures the airflow in a main supply
duct by using a Pitot-tube traverse. His measurement is 1,200 fpm. The area of the duct
at the point of measurement is 10" X 30". He says that he has 2,500 cfm. Which
technician is correct: - Answers- Both technicians are correct
When should the dampers and registers of a new system be 100% open: - Answers- on
initial startup of the system
Technician A says that an 8" X 12" register that has the velocity of 300 fpm with a free
area of 75% has an air quantity of 150 cfm. Technician B says that an 8" X 12" register
that has the velocity of 300 fpm with a free area of 75% has an air quantity of 250 cfm.
Which technician is correct: - Answers- technician A
A service call is made on the complaint of not enough warm air out of the supply
registers. The technician does an airflow calculation by measuring the temperature
difference across the heat exchanger, which is 100° F. He then determines the furnace
output, which is 90,000 Btu/h. With this information, he can determine the quantity of
airflow out of the system. Which of the following formulas must be used: - Answers-
cfm= [Output (Btu/h)] / (1.08 X temperature rise)
QUESTIONS AND ANSWERS
An air conditioning service call is made and the complaint is that the system does not
seem to be cooling properly. It is noticed that the suction line and the evaporator coil are
frosted up. The filter is checked and it is clean. It is suspected that the indoor blower is
not operating at the proper speed. Technician A says that the speed can be verified with
a strobe tachometer to be sure that the rpms are as written on the nameplate.
Technician B says that the airflow can be measured by taking a static pressure reading.
Which technician is correct? - Answers- technician A
An airflow measurement taken in a duct system by drilling small holes in a vertical and
horizontal section of a rectangular duct to find an average air velocity reading is known
as: - Answers- a Pitot-tube traverse
To calculate velocity pressure when using a manometer, which of the following would be
the proper formula: - Answers- total pressure-static pressure= velocity pressure
What is the primary purpose of an isolation collar: - Answers- It is used to eliminate
furnace vibration through the duct system
Technician A measures the airflow in a main supply duct by using a Pitot-tube traverse.
His measurement is 1,200 fpm. The area of the duct at the point of measurement is 8" X
30". He says that he has 2,000 cfm. Technician B measures the airflow in a main supply
duct by using a Pitot-tube traverse. His measurement is 1,200 fpm. The area of the duct
at the point of measurement is 10" X 30". He says that he has 2,500 cfm. Which
technician is correct: - Answers- Both technicians are correct
When should the dampers and registers of a new system be 100% open: - Answers- on
initial startup of the system
Technician A says that an 8" X 12" register that has the velocity of 300 fpm with a free
area of 75% has an air quantity of 150 cfm. Technician B says that an 8" X 12" register
that has the velocity of 300 fpm with a free area of 75% has an air quantity of 250 cfm.
Which technician is correct: - Answers- technician A
A service call is made on the complaint of not enough warm air out of the supply
registers. The technician does an airflow calculation by measuring the temperature
difference across the heat exchanger, which is 100° F. He then determines the furnace
output, which is 90,000 Btu/h. With this information, he can determine the quantity of
airflow out of the system. Which of the following formulas must be used: - Answers-
cfm= [Output (Btu/h)] / (1.08 X temperature rise)
