NATE Heat Pump Install flashcards
NATE Heat Pump Install · 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.
- Coefficient of Performance (COP)
- Ratio of heating or cooling capacity delivered in Btu/h to electrical input in Btu/h. HSPF2 approximates COP multiplied by 3.412, adjusted for defrost cycles and cycling losses.
- Heating balance point
- Outdoor temperature at which heat pump capacity equals the building's heat loss. Below this point, auxiliary heat makes up the deficit; it should sit at or below design outdoor temperature.
- Superheat calculation
- Suction line temperature minus the evaporating saturation temperature obtained from suction pressure. Fixed-orifice systems use a load-dependent target, typically 5 to 15°F.
- Subcooling calculation
- Condensing saturation temperature minus liquid line temperature. TXV or EEV systems target the nameplate value, commonly 8 to 12°F, to confirm proper charge.
- Reversing valve function
- Pilot-operated four-way valve that swaps evaporator and condenser roles between coils. Energizing the solenoid usually selects cooling mode on residential systems.
- Accumulator purpose
- Suction-line vessel that traps liquid refrigerant and oil before the compressor. Heat pumps require one because defrost and low-load operation can flood the suction line.
- Manual J design temperatures
- Heating design uses the 99% winter design dry bulb and cooling design uses the 1% summer design dry bulb for the specific location, taken from ASHRAE or NOAA tables.
- Sensible heat airflow formula
- Btu/h equals 1.08 times CFM times temperature difference at sea level. At altitude, multiply the 1.08 factor by the air density ratio to correct for thinner air.
- Equipment sizing tolerance
- Total capacity should fall within 100 to 115% of the calculated total load, and sensible capacity must meet sensible load at design conditions to control humidity and cycling.
- Line-set capacity correction
- Manufacturer tables reduce nominal capacity as equivalent length and vertical separation increase, typically 1 to 3% per 10 ft beyond the base 25 ft length.
- Minimum circuit ampacity
- MCA equals 1.25 times the largest motor's rated load amps plus all other loads. Conductors must be sized at or above MCA, and the breaker must not exceed nameplate MOP.
- Thermostat control colors
- R is 24V hot, C is common, Y is compressor, G is blower, W is auxiliary heat, O activates reversing valve in cooling, and B activates it in heating.
- R-to-C voltage test
- Measure 24VAC between R and C under load. A reading below 20VAC indicates transformer overload, undersized control wire, or a shorted or overloaded control circuit.
- Disconnect location rule
- A disconnecting means must be within sight of and within 50 ft of the outdoor unit. A non-fused pull-out is acceptable when the branch breaker provides overcurrent protection.
- Nitrogen purge during brazing
- Flow dry nitrogen at roughly 2 to 3 SCFH through the tubing while brazing to prevent internal oxidation. Leave one point open so pressure cannot build.
- Standing vacuum test
- Isolate the pump at 500 microns and hold 10 to 15 minutes. A rise to 1,000 to 2,000 microns indicates moisture; a rise above 2,000 microns indicates a leak.
- Triple evacuation procedure
- Evacuate to about 1,500 microns, break the vacuum with dry nitrogen to 0 psig, repeat, then pull a final vacuum to 500 microns or lower before charging.
- Weigh-in charging
- Charge by weight using a scale when the line set exceeds factory charge or the system has a fixed orifice. Add refrigerant per the manufacturer's ounces-per-foot table.
- Nominal cooling airflow
- About 400 CFM per ton is standard. Lower to 350 CFM per ton for better latent removal in humid climates, or raise to 450 CFM per ton for sensible capacity in dry climates.
- External static pressure budget
- Sum pressure drops across filter, coil, supply trunk, branches, and return. The total must stay within the blower's rated external static pressure from the table.
- Return air requirement
- Heat pumps need a ducted or fully panned return. Undersized return reduces airflow, raises superheat, and can freeze the indoor coil during cooling operation.
- Condensate drain leveling
- Indoor units must be level within about 1/4 in. per foot so condensate drains. A secondary pan with a float switch is required where overflow could cause damage.
- Outdoor unit clearances
- Follow the installation manual, typically 12 to 18 in. on the service side, 12 in. at the fan discharge, 6 to 12 in. on other sides, and 24 to 36 in. above grade.
- Defrost cycle sequence
- The reversing valve shifts to cooling, the outdoor fan stops, strip heat energizes, and the coil warms to the termination temperature before normal heating resumes.
- Defrost drain protection
- Route defrost condensate away from the foundation. Use a heated drain pan or drain-line heat tape where freezing temperatures would otherwise block the drain path.
- Cooling temperature split
- Return minus supply air temperature should be about 18 to 22°F at 400 CFM per ton and 50% indoor relative humidity. A split under 15°F suggests low airflow or charge.
- Commissioning stabilization time
- Run the system in cooling for 15 to 20 minutes before recording superheat, subcooling, pressures, and amp draw so readings reflect steady-state operation.
- Amp draw verification
- Compare measured compressor amps to nameplate rated load amps. Readings well above RLA indicate high head pressure, low voltage, or a failing compressor or capacitor.
- Low suction with high superheat
- Indicates an underfed evaporator from low airflow, a restricted piston or TXV, or low charge. Check airflow and the metering device before adding refrigerant.
- Capacitor test method
- Measure microfarads with a meter and compare to the rated value, typically within plus or minus 6%. A bulged case or low reading means replacement.
- Section 608 certification
- EPA credential required to purchase or handle regulated refrigerants. Type I covers small appliances, Type II high-pressure systems, Type III low-pressure, and Universal covers all.
- A2L refrigerant requirements
- R-32 and R-454B are mildly flammable A2L refrigerants. They require A2L-rated components, leak detection, and charge limits set by ASHRAE 15 and model codes.