Mixed Deck — All NATE Topics Flashcards
100 cards from real NATE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 20 Mixed Deck — All NATE Topics flashcards as text
What component in an oil burner atomizes the fuel oil and mixes it with air for combustion?
Answer: Nozzle
The nozzle atomizes oil into a fine spray at a precise angle and pattern, mixing it with combustion air for efficient burning.
What is the correct method for measuring total external static pressure (TESP) on an air handler?
Answer: Measure static pressure in the return plenum before the coil and in the supply plenum after the coil, then subtract return from supply
TESP = supply static pressure minus return static pressure (both measured close to the air handler), giving total system resistance.
What type of compressor is most commonly used in large commercial refrigeration rack systems?
Answer: Reciprocating (semi-hermetic)
Semi-hermetic reciprocating compressors are widely used in commercial rack systems because they are serviceable and available in a wide range of capacities.
What is the purpose of the vent pressure switch on a two-stage condensing furnace?
Answer: Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition
The vent pressure switch proves adequate draft by sensing the negative pressure created by the inducer blower before the gas valve is energized.
What is the standard line voltage for most residential HVAC equipment in the United States?
Answer: 240V/60Hz
Most residential HVAC equipment in the US operates on 240V single-phase 60Hz power.
What is the typical target evaporator superheat range for a fixed-orifice metering device system?
Answer: 10–18°F
A fixed-orifice system typically targets 10–18°F of superheat at the evaporator outlet for proper refrigerant feed.
Which component in an HVAC control circuit is used to sense thermostat demand and energize the compressor contactor?
Answer: Control relay
A control relay receives the low-voltage thermostat signal and switches the higher-voltage circuit to energize the compressor contactor.
What is the recommended insulation R-value for ducts installed in unconditioned attics in most US climate zones?
Answer: R-8
Most US energy codes and ACCA guidelines recommend R-8 duct insulation for ducts in unconditioned attic spaces to minimize heat gain or loss.
What is Manual J used for in residential HVAC design?
Answer: Calculating heating and cooling loads for a structure
ACCA Manual J is the industry-standard load calculation procedure that determines the BTU capacity required to heat and cool a home.
What does a TXV (thermostatic expansion valve) use to control refrigerant flow?
Answer: Suction line superheat sensed by a bulb
A TXV senses evaporator outlet superheat via a sensing bulb and adjusts flow to maintain a set superheat.
Which NEC article governs the installation of HVAC equipment in commercial and residential applications?
Answer: Article 440
NEC Article 440 specifically covers air-conditioning and refrigerating equipment, including wiring, overcurrent protection, and disconnects.
What is the standard gas manifold pressure for natural gas residential furnaces in the US?
Answer: 3.2–3.8 inches WC
Natural gas furnace manifold pressure is typically set at 3.2–3.8 inches water column (around 3.5 inches WC nominal).
What is the purpose of a balancing damper in a duct branch?
Answer: Adjust airflow to individual zones to balance the system and deliver correct CFM to each room
Balancing dampers restrict airflow in over-supplied branches, diverting more air to under-supplied areas for proper room-by-room comfort.
Which tool is used to measure the wet-bulb temperature when evaluating air conditioning performance?
Answer: Sling psychrometer
A sling psychrometer uses a wet-bulb and dry-bulb thermometer to measure relative humidity and wet-bulb temperature.
What does a low suction pressure reading typically indicate in a residential AC system?
Answer: Low refrigerant charge or restricted airflow
Low suction pressure usually points to insufficient refrigerant or reduced evaporator airflow causing lower evaporating temperatures.
What component allows a heat pump to reverse the refrigeration cycle between heating and cooling modes?
Answer: Reversing valve
The reversing valve redirects refrigerant flow so the indoor coil acts as a condenser in heating mode and an evaporator in cooling mode.
What does the label 'R' on an HVAC thermostat terminal typically represent?
Answer: 24V AC power from the transformer
The 'R' terminal supplies 24V AC power from the control transformer to the thermostat and control circuit.
During a heating cycle, which coil in a heat pump acts as the evaporator?
Answer: Outdoor coil
In heating mode, the outdoor coil absorbs heat from the outside air (acting as evaporator) and the indoor coil releases heat (acting as condenser).
What is flash gas and where does it occur in the refrigeration cycle?
Answer: Refrigerant that vaporizes as pressure drops across the metering device before reaching the evaporator
Flash gas forms when liquid refrigerant loses pressure at the metering device, absorbing no useful heat and reducing system capacity.
What EPA regulation governs refrigerant handling and requires recovery before service of commercial refrigeration equipment?
Answer: EPA Section 608
EPA Section 608 prohibits venting refrigerants and requires certified technicians to recover refrigerant before opening any refrigerant circuit.