NATE AC Service Certification Exam Questions and Correct Rationales Graded A+

A system is supplied from the factory with a charge of 5 pounds 10 ounces for a 15 foot line set. The line set is 25 feet long. The manufacturer's instruction sheet specifies 0.6 ounces of refrigeration to be added for each added foot of refrigerant line set length. What is the total refrigerant charge for the system? A. 6 ounces B. 5 pounds C. 5 pounds 10 ounces D. 6 pounds - Answer: D. 6 pounds 25ft - 15ft = 10ft 10ft x .6 = 6 ounces 5 pounds + 10 ounces + 6 ounces 5 pounds + 16 ounces = 6 pounds Return air leakage in a hot attic will: A. Increase capacity B. Decrease capacity C. Increase airflow D. Decrease airflow - Answer: B. Decrease capacity Which of the following substances could create an extremely dangerous condition if used to check refrigeration system for leaks? A. R-22 B. Nitrogen C. Oxygen D. Carbon Dioxide - Answer: D. Carbon Dioxide On a 3 ton unit installation, the measure airflow equals 1550 CFM. What does this indicate? A. Proper balancing B. Low Airflow C. Excess airflow D. Improper balancing - Answer: C. Excess airflow(400cfm per ton, 3 ton=1200cfm) What will refrigerant oil in a hose cause when a technician is checking the pressures in an operation system with a manifold gauge set? A. All readings on that gauge will increase in value. B. All readings on that gauge will decrease in value. C. All readings on that gauge will not be affected. D. The gauge will read 0 psig. - Answer: C. All readings on that gauge will not be affected. Which of the following is a likely problem if the air across the evaporator of an air conditioner has a high temperature differential? A. Too much charge B. Clogged expansion valve C. Dirty filter or evaporator D. Dirty condenser coil - Answer: C When performing a cycling check during a maintenance call, the technician should first check with the owner of the equipment for their opinion of performance. The next step is to turn the unit off at the thermostat SYSTEM switch. The technician should set the FAN switch to: A. AUTO and measure the voltage from the R to G terminal. B. ON and measure the voltage from the R to the W1 terminal. C. ON and check that the blower is running. D. AUTO and check that the blower is running. - Answer: C On a residential no cooling call, typically the first check would be: A. the air filter. B. the control voltage at the transformer. C. if the thermostat is calling for cooling. D. the refrigerant system pressures. - Answer: C. if the thermostat is calling for cooling. What could cause a customer to complain that their home feels damp or "sticky"? A. Low evaporator airflow B. Returns may be pulling in unconditioned air C. The system is undersized D. Air filter is clogged or dirty - Answer: B. Returns may be pulling in unconditioned air A system supply airflow check is used to diagnose: A. humidity problems. B. compressor overheating. C. restricted liquid line drier D. condenser fan motor overheating. - Answer: A. humidity problems. A technician finds a R-410A system with the following: *Suction pressure is 105 psi *Suction line temperature is 75degF *Recommended superheat is 20degF This indicates the system: A. is overcharged. B. has excess airflow C. is undercharged. D. has low airflow - Answer: C. is undercharged. When an air conditioner with a thermostatic expansion valve installed is overcharged, the excess charge should be removed by recovering some charge and checking: A. system pressures. B. superheat. C. subcooling. D. head pressure. - Answer: *C. subcooling With an R-410A condensing pressure of 397 psig and a liquid line temperature of 108degF, what is the subcooling temperature? A. 36degF B. 24degF C. 16degF D. 8degF - Answer: D. 8 deg F With the thermostat blower switch set to ON, which of the following measurements indicates a call for residential indoor blower operation? A. 0 volts at the load side of the relay B. 24 volts at the load side of the relay C. 0 volts at the relay coil D. 24 volts at the relay coil - Answer: *B Which mfd value indicates a good start capacitor rated at 145-175 mfd? A. 130 B. 160 C. 180 D. 190 - Answer: B. 160 A system with a reciprocating compressor is pumped down and the power is shut off. If the suction pressure rises very rapidly, this is an indication that the: