NATE Exam: Air Conditioning and Heat Pumps

Use the collected service data below to calculate the air flow volume for a residential electric furnace: Voltage = 240 V ac Current draw = 40 A Entering air temperature = 70°F Leaving air temperature = 105°F a. 798 cfm b. 867 cfm c, 936 cfm d. 1,100 cfm cfm = (voltage x current x 3.413) / (temperature rise x 1.08) - Correct Solution b (867 cfm) What is the maximum recommended face velocity for air leaving a supply register? a. 300 ft/min b. 450 ft/min c. 500 ft/min d. 700 ft/min - Correct Solution d (700 ft/min) Temperature readings taken on the refrigerant discharge line 6 in. from the compressor must never exceed ____°F. a. 150°F b. 175°F c. 200°F d. 225°F - Correct Solution d (225°F) What problem results when the limit temperature of the discharge line at the compressor is exceeded? a. Evaporator superheat will be excessive, causing capacity loss b. Gassing of the indoor metering device will occur during the cooling cycle c. Subcooling in the condenser will decline to a dangerously low level d. Temperature in the compressor will be high enough to vaporize the lubricant - Correct Solution d (Temperature in the compressor will be high enough to vaporize the lubricant) A system should be operated for at least ____ before heat measurements are taken. a. 20 minutes b. 30 minutes c. 45 minutes d. 1 hour - Correct Solution a (20 minutes) What level of vacuum is needed to ensure that a sufficiently deep vacuum has been drawn for the removal of water vapor? a. 500 microns b. 1,000 microns c. 2,500 microns d. 25,000 microns - Correct Solution a (500 microns) What potential problem is associated with the use of dye injected for the purpose of leak detection? a. Dye can damage a technician's refrigerant manifold gauges b. Dye can increase the pumping ratio of the compressor c. Overuse of dye can change the mixing properties of refrigerant and oil d. Overuse of due can create acids in the oil See page 186 - Correct Solution c (Overuse of dye can change the mixing properties of refrigerant and oil) What gas must be purged through a refrigerant circuit to prevent the formation of oxides whenever brazing is being done? a. Any HFC b. Dry nitrogen c. Filtered air d. Oxygen - Correct Solution b (Dry nitrogen) What certification is required before a technician is permitted to work on air conditioning and heat pump systems? a. ARI 77-88 certification b. EPA Section 608 certification c. EPA Section 609 certification d. Journey or Master Mechanical tradesman license - Correct Solution b (EPA Section 608 certification) The maximum temperature at which refrigerant may be stored is ____°F when the container is no more than ____% full of liquid by volume. a. 120°F, 60% b. 125°F, 60% c. 125°F, 80% d. 135°F, 80% - Correct Solution c (125°F, 80%) Boiling of the refrigerant occurs in which system component? a. Compressor b. Condenser c. Evaporator d. Metering device - Correct Solution c (Evaporator) Why is superheat necessary in a system that utilizes hermetic compressors? a. It ensures that dry vapor reaches the compressor so that mechanical damage does not occur b. It increases system capacity c. It prevents liquid refrigerant from gassing the metering device d. Superheat is necessary only when open compressors are being used - Correct Solution a (It ensures that dry vapor reaches the compressor so that mechanical damage does not occur) When the heat load on an evaporator increases, what is the effect on the system? a. Suction pressure decreases and discharge pressure increases b. Suction pressure increases and discharge pressure decreases c. Suction pressure and discharge pressure both decrease d. Suction pressure and discharge pressure both increase - Correct Solution d (Suction pressure and discharge pressure both increase) What type of energy is transferred when work is done in the condenser? a. Latent heat energy b. Sensible heat energy c. Both latent and sensible heat energy d. Neither latent nor sensible heat energy - Correct Solution c (Both latent and sensible heat energy)