NATE AC Installation flashcards
NATE AC Installation · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Design indoor cooling condition
- ARI standard rating condition is 80°F dry bulb and 67°F wet bulb indoors, with 95°F dry bulb outdoor air.
- Nominal cooling airflow
- 400 cfm per ton of cooling capacity is the nominal value; the acceptable range is roughly 350 to 450 cfm per ton.
- Evaporator temperature split
- The dry-bulb temperature difference between return air and supply air; typical cooling range is 16°F to 22°F at design airflow.
- Superheat charging method
- Used with fixed-orifice or piston metering devices; measure suction line temperature minus saturation temperature, targeting about 8°F to 12°F.
- Subcooling charging method
- Used with thermostatic expansion valves; measure liquid line temperature minus saturation temperature, targeting about 8°F to 12°F per manufacturer.
- Dry bulb vs wet bulb
- Dry bulb measures sensible air temperature; wet bulb measures temperature with evaporative cooling and indicates moisture content and latent load.
- Heat pump balance point
- Outdoor temperature where heat pump capacity equals building heat load; below it, auxiliary or emergency heat must supplement.
- TXV sensing bulb
- The bulb clamps to the suction line and senses evaporator outlet temperature; it modulates refrigerant flow to maintain superheat.
- Filter drier arrow
- The arrow on the filter drier marks refrigerant flow direction; bi-flow driers are required on heat pumps for reverse-cycle operation.
- Suction line insulation
- Vapor suction lines are insulated to prevent heat gain and condensation; liquid lines are generally not insulated except in high-humidity spaces.
- Condensate trap depth
- The trap depth must exceed the blower's negative static pressure in inches of water column, typically 2 to 4 inches.
- Reversing valve function
- A pilot-operated valve that swaps evaporator and condenser roles by redirecting refrigerant flow for heating or cooling.
- Crankcase heater purpose
- Keeps compressor oil warm when idle to prevent refrigerant migration and liquid slugging at startup.
- Accumulator purpose
- Installed on the suction line of heat pumps to hold liquid refrigerant and prevent it from reaching the compressor.
- ASHRAE 62.2 ventilation rate
- Whole-house ventilation formula: Q = 0.03A + 7.5(N+1) cfm, where A is floor area and N is bedrooms.
- MERV filter rating
- MERV rates particle capture; MERV 8 is common residential, MERV 13 offers higher filtration with higher pressure drop.
- Return air prohibition
- Return air must not be drawn from bathrooms, kitchens, garages, or rooms with combustion appliances unless specifically engineered.
- Indoor relative humidity range
- Comfort and mold prevention typically target 30% to 50% relative humidity; sustained levels above 60% support biological growth.
- Carbon monoxide exposure limits
- EPA limits are 9 ppm for 8 hours and 35 ppm for 1 hour; combustion appliance testing uses these as reference thresholds.
- Filter pressure drop
- A clean residential filter typically drops 0.1 to 0.2 inches water column; excessive drop reduces airflow and capacity.
- Ohm's law
- Voltage equals current times resistance (E = I × R); power equals voltage times current (P = E × I).
- Run capacitor tolerance
- A run capacitor is normally good within plus or minus 6% to 10% of its rated microfarad value; bulging indicates replacement.
- Thermostat C terminal
- The common terminal provides 24-volt power to the thermostat; it completes the control circuit and supports smart thermostats.
- Disconnect location rule
- The service disconnect must be within sight of and not more than 50 feet from the equipment it controls.
- MCA and MOP
- Minimum circuit ampacity is the minimum conductor rating; maximum overcurrent protection is the largest breaker or fuse permitted.
- Winding resistance balance
- Compressor run, start, and common winding resistances should balance within about 10%; a large imbalance suggests a damaged winding.
- Sensible heat formula
- Sensible Btu/h = 1.08 × cfm × dry-bulb temperature difference at sea level; 1.08 derives from air density and specific heat.
- Total heat formula
- Total Btu/h = 4.5 × cfm × enthalpy difference; 4.5 equals 60 minutes times 0.075 pounds per cubic foot.
- Total external static pressure
- TESP is the sum of supply and return static pressures measured across the blower; residential equipment typically rates near 0.5 inches water column.
- Evacuation micron level
- A properly evacuated system holds below 500 microns with the vacuum pump isolated; a rising reading indicates leaks or moisture.
- Nitrogen leak test pressure
- Pressure-test with dry nitrogen, commonly 150 to 300 psi for residential split systems, never with refrigerant or oxygen.
- Low superheat diagnosis
- Low superheat with high suction pressure suggests overcharge or excess airflow; low superheat with low suction suggests restriction or low load.