NCCER HVACR cheat sheet

HVACR covers heating, ventilation, air conditioning, and refrigeration; the R distinguishes refrigeration (industrial and commercial process cooling) from comfort air conditioning.

Sensible heat changes a substance's temperature without changing phase; latent heat changes phase at constant temperature (melting, boiling, condensing).

1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW; it is the heat absorption rate of melting one ton of ice in 24 hours.

Heat always flows from higher to lower temperature; cooling does not add cold, it removes heat and moves it to a warmer location.

British thermal unit (Btu) is the heat needed to raise 1 lb of water 1°F; 1 Btu = 1.055 kJ, and 1 watt = 3.412 Btu/h.

Air composition by volume is about 78% nitrogen, 21% oxygen, and 1% other gases; comfort cooling typically targets 75°F and about 50% relative humidity.

Temperature conversions: °F = (°C × 1.8) + 32; °C = (°F − 32) ÷ 1.8; absolute scales are Rankine (°R = °F + 460) and Kelvin (K = °C + 273).

Refrigerant phase change is the core mechanism: evaporator absorbs latent heat at low pressure, condenser rejects latent heat at high pressure.

Lockout/tagout (LOTO): isolate energy, lock the disconnect, tag it, and verify zero energy before servicing; never rely on a switch position alone.

Personal protective equipment for refrigerant work includes safety glasses or goggles, gloves, long sleeves, and ventilation; liquid refrigerant contact causes frostbite.

Refrigerant cylinders are stored upright, secured, below 125°F, and never filled above 80% liquid full to allow expansion; oxygen and acetylene are stored separately.

Manifold gauge set: blue hose to low side (suction), red to high side (discharge), yellow to vacuum pump or recovery cylinder; never use hoses for both refrigerant and nitrogen without purging.

Micron gauge measures deep vacuum in microns; 1 micron = 1/25,400 mmHg; a standing vacuum below 500 microns indicates an acceptable dehydration level.

Electrical meter safety: verify CAT rating, test the meter on a known live source, and treat all conductors as energized; clamp meters read current without breaking the circuit.

Torch brazing requires a fire extinguisher, a fire watch, and nitrogen purge to prevent internal oxidation (scale) in copper lines.

Recovery, recycling, and reclamation are distinct: recovery removes refrigerant, recycling cleans it on site, reclamation restores it to ARI-700 purity at a processing facility.

Vapor-compression cycle order: compressor → condenser → metering device → evaporator → back to compressor; the compressor raises pressure and temperature.

Superheat = actual suction line temperature − evaporating (saturation) temperature; it confirms the evaporator is fully fed and protects the compressor from liquid.

Subcooling = condensing (saturation) temperature − liquid line temperature; it confirms the condenser is fully condensing and the liquid seal at the metering device.

TXV/EEV charge is set by superheat; a fixed orifice (piston) is sized by capacity, and superheat varies with load and outdoor temperature.

Pressure–temperature (PT) chart converts saturation pressure to temperature for a given refrigerant; each refrigerant has its own curve and glide (zeotropic blends).

Refrigerant types: CFCs (R-12), HCFCs (R-22), HFCs (R-410A, R-134a), and HFOs (R-1234yf); R-410A operates at roughly 50–60% higher pressure than R-22 and requires POE oil.

Evaporator superheat too high with low suction pressure suggests undercharge, a restricted metering device, or a blocked liquid line; frost on the coil indicates low airflow or low charge.

Airflow across the evaporator is typically 350–450 CFM per ton; low airflow drops suction pressure and can freeze the coil.

Gas furnace sequence: thermostat call → inducer draft motor → pressure switch proves draft → igniter → gas valve opens → flame sensor proves flame → blower delay → blower on.

Combustion air requirements: approximately 50 cubic feet per 1,000 Btu/h input for confined spaces with outdoor air; inadequate air causes incomplete combustion and CO.

Flue gas CO2 target is about 8–10% with 4–6% O2 for natural gas; elevated CO (over 100 ppm in flue, or any CO in room air) indicates a problem.

Gas manifold pressure for natural gas is typically 3.5 in. w.c.; LP is about 10–11 in. w.c.; always check the data plate.

Furnace efficiency: AFUE (annual fuel utilization efficiency) of 90%+ indicates a condensing furnace with a secondary heat exchanger and PVC venting.

Electric heat: 1 kW = 3,412 Btu/h; resistance heat strips are checked by amp draw and ohm readings against the nameplate.

Heat pump balance point is the outdoor temperature where heat pump capacity equals building load; below it, auxiliary or emergency heat supplements.

Defrost cycle on a heat pump reverses the refrigerant flow or stops the outdoor fan to melt frost on the outdoor coil; the system must terminate on temperature or time.

Line sizing and routing: keep suction lines short and insulated, slope horizontal suction lines toward the compressor, and avoid oil traps except where required for risers.

Evacuation: triple evacuation with nitrogen sweep to below 500 microns; a rising vacuum indicates moisture or a leak.

Leak detection order: electronic leak detector, soap bubbles, and nitrogen pressure test; never use oxygen or compressed air to pressure test refrigerant systems.

Charging methods: weigh-in for new systems and critically charged units; superheat method for fixed orifice; subcooling method for TXV systems.

Electrical troubleshooting: check voltage at the contactor, control transformer output (24 V), and thermostat continuity; a tripped high-pressure or low-pressure switch points to airflow or charge.

Diagnostic pattern: high head pressure with high subcooling = overcharge or condenser airflow restriction; low suction with high superheat = undercharge or restriction.

Airflow verification: static pressure across the blower and filter, plus temperature rise (furnace) or temperature drop (AC, typically 15–20°F) confirm proper airflow.

HVACR covers heating, ventilation, air conditioning, and refrigeration; the R distinguishes refrigeration (industrial and commercial process cooling) from comfort air conditioning.

Sensible heat changes a substance's temperature without changing phase; latent heat changes phase at constant temperature (melting, boiling, condensing).

1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW; it is the heat absorption rate of melting one ton of ice in 24 hours.

Heat always flows from higher to lower temperature; cooling does not add cold, it removes heat and moves it to a warmer location.

British thermal unit (Btu) is the heat needed to raise 1 lb of water 1°F; 1 Btu = 1.055 kJ, and 1 watt = 3.412 Btu/h.

Air composition by volume is about 78% nitrogen, 21% oxygen, and 1% other gases; comfort cooling typically targets 75°F and about 50% relative humidity.

Temperature conversions: °F = (°C × 1.8) + 32; °C = (°F − 32) ÷ 1.8; absolute scales are Rankine (°R = °F + 460) and Kelvin (K = °C + 273).

Refrigerant phase change is the core mechanism: evaporator absorbs latent heat at low pressure, condenser rejects latent heat at high pressure.

Lockout/tagout (LOTO): isolate energy, lock the disconnect, tag it, and verify zero energy before servicing; never rely on a switch position alone.

Personal protective equipment for refrigerant work includes safety glasses or goggles, gloves, long sleeves, and ventilation; liquid refrigerant contact causes frostbite.

Refrigerant cylinders are stored upright, secured, below 125°F, and never filled above 80% liquid full to allow expansion; oxygen and acetylene are stored separately.

Manifold gauge set: blue hose to low side (suction), red to high side (discharge), yellow to vacuum pump or recovery cylinder; never use hoses for both refrigerant and nitrogen without purging.

Micron gauge measures deep vacuum in microns; 1 micron = 1/25,400 mmHg; a standing vacuum below 500 microns indicates an acceptable dehydration level.

Electrical meter safety: verify CAT rating, test the meter on a known live source, and treat all conductors as energized; clamp meters read current without breaking the circuit.

Torch brazing requires a fire extinguisher, a fire watch, and nitrogen purge to prevent internal oxidation (scale) in copper lines.

Recovery, recycling, and reclamation are distinct: recovery removes refrigerant, recycling cleans it on site, reclamation restores it to ARI-700 purity at a processing facility.

Vapor-compression cycle order: compressor → condenser → metering device → evaporator → back to compressor; the compressor raises pressure and temperature.

Superheat = actual suction line temperature − evaporating (saturation) temperature; it confirms the evaporator is fully fed and protects the compressor from liquid.

Subcooling = condensing (saturation) temperature − liquid line temperature; it confirms the condenser is fully condensing and the liquid seal at the metering device.

TXV/EEV charge is set by superheat; a fixed orifice (piston) is sized by capacity, and superheat varies with load and outdoor temperature.

Pressure–temperature (PT) chart converts saturation pressure to temperature for a given refrigerant; each refrigerant has its own curve and glide (zeotropic blends).

Refrigerant types: CFCs (R-12), HCFCs (R-22), HFCs (R-410A, R-134a), and HFOs (R-1234yf); R-410A operates at roughly 50–60% higher pressure than R-22 and requires POE oil.

Evaporator superheat too high with low suction pressure suggests undercharge, a restricted metering device, or a blocked liquid line; frost on the coil indicates low airflow or low charge.

Airflow across the evaporator is typically 350–450 CFM per ton; low airflow drops suction pressure and can freeze the coil.

Gas furnace sequence: thermostat call → inducer draft motor → pressure switch proves draft → igniter → gas valve opens → flame sensor proves flame → blower delay → blower on.

Combustion air requirements: approximately 50 cubic feet per 1,000 Btu/h input for confined spaces with outdoor air; inadequate air causes incomplete combustion and CO.

Flue gas CO2 target is about 8–10% with 4–6% O2 for natural gas; elevated CO (over 100 ppm in flue, or any CO in room air) indicates a problem.

Gas manifold pressure for natural gas is typically 3.5 in. w.c.; LP is about 10–11 in. w.c.; always check the data plate.

Furnace efficiency: AFUE (annual fuel utilization efficiency) of 90%+ indicates a condensing furnace with a secondary heat exchanger and PVC venting.

Electric heat: 1 kW = 3,412 Btu/h; resistance heat strips are checked by amp draw and ohm readings against the nameplate.

Heat pump balance point is the outdoor temperature where heat pump capacity equals building load; below it, auxiliary or emergency heat supplements.

Defrost cycle on a heat pump reverses the refrigerant flow or stops the outdoor fan to melt frost on the outdoor coil; the system must terminate on temperature or time.

Line sizing and routing: keep suction lines short and insulated, slope horizontal suction lines toward the compressor, and avoid oil traps except where required for risers.

Evacuation: triple evacuation with nitrogen sweep to below 500 microns; a rising vacuum indicates moisture or a leak.

Leak detection order: electronic leak detector, soap bubbles, and nitrogen pressure test; never use oxygen or compressed air to pressure test refrigerant systems.

Charging methods: weigh-in for new systems and critically charged units; superheat method for fixed orifice; subcooling method for TXV systems.

Electrical troubleshooting: check voltage at the contactor, control transformer output (24 V), and thermostat continuity; a tripped high-pressure or low-pressure switch points to airflow or charge.

Diagnostic pattern: high head pressure with high subcooling = overcharge or condenser airflow restriction; low suction with high superheat = undercharge or restriction.

Airflow verification: static pressure across the blower and filter, plus temperature rise (furnace) or temperature drop (AC, typically 15–20°F) confirm proper airflow.

HVACR covers heating, ventilation, air conditioning, and refrigeration; the R distinguishes refrigeration (industrial and commercial process cooling) from comfort air conditioning.

Sensible heat changes a substance's temperature without changing phase; latent heat changes phase at constant temperature (melting, boiling, condensing).

1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW; it is the heat absorption rate of melting one ton of ice in 24 hours.

Heat always flows from higher to lower temperature; cooling does not add cold, it removes heat and moves it to a warmer location.

British thermal unit (Btu) is the heat needed to raise 1 lb of water 1°F; 1 Btu = 1.055 kJ, and 1 watt = 3.412 Btu/h.

Air composition by volume is about 78% nitrogen, 21% oxygen, and 1% other gases; comfort cooling typically targets 75°F and about 50% relative humidity.

Temperature conversions: °F = (°C × 1.8) + 32; °C = (°F − 32) ÷ 1.8; absolute scales are Rankine (°R = °F + 460) and Kelvin (K = °C + 273).

Refrigerant phase change is the core mechanism: evaporator absorbs latent heat at low pressure, condenser rejects latent heat at high pressure.

Lockout/tagout (LOTO): isolate energy, lock the disconnect, tag it, and verify zero energy before servicing; never rely on a switch position alone.

Personal protective equipment for refrigerant work includes safety glasses or goggles, gloves, long sleeves, and ventilation; liquid refrigerant contact causes frostbite.

Refrigerant cylinders are stored upright, secured, below 125°F, and never filled above 80% liquid full to allow expansion; oxygen and acetylene are stored separately.

Manifold gauge set: blue hose to low side (suction), red to high side (discharge), yellow to vacuum pump or recovery cylinder; never use hoses for both refrigerant and nitrogen without purging.

Micron gauge measures deep vacuum in microns; 1 micron = 1/25,400 mmHg; a standing vacuum below 500 microns indicates an acceptable dehydration level.

Electrical meter safety: verify CAT rating, test the meter on a known live source, and treat all conductors as energized; clamp meters read current without breaking the circuit.

Torch brazing requires a fire extinguisher, a fire watch, and nitrogen purge to prevent internal oxidation (scale) in copper lines.

Recovery, recycling, and reclamation are distinct: recovery removes refrigerant, recycling cleans it on site, reclamation restores it to ARI-700 purity at a processing facility.

Vapor-compression cycle order: compressor → condenser → metering device → evaporator → back to compressor; the compressor raises pressure and temperature.

Superheat = actual suction line temperature − evaporating (saturation) temperature; it confirms the evaporator is fully fed and protects the compressor from liquid.

Subcooling = condensing (saturation) temperature − liquid line temperature; it confirms the condenser is fully condensing and the liquid seal at the metering device.

TXV/EEV charge is set by superheat; a fixed orifice (piston) is sized by capacity, and superheat varies with load and outdoor temperature.

Pressure–temperature (PT) chart converts saturation pressure to temperature for a given refrigerant; each refrigerant has its own curve and glide (zeotropic blends).

Refrigerant types: CFCs (R-12), HCFCs (R-22), HFCs (R-410A, R-134a), and HFOs (R-1234yf); R-410A operates at roughly 50–60% higher pressure than R-22 and requires POE oil.

Evaporator superheat too high with low suction pressure suggests undercharge, a restricted metering device, or a blocked liquid line; frost on the coil indicates low airflow or low charge.

Airflow across the evaporator is typically 350–450 CFM per ton; low airflow drops suction pressure and can freeze the coil.

Gas furnace sequence: thermostat call → inducer draft motor → pressure switch proves draft → igniter → gas valve opens → flame sensor proves flame → blower delay → blower on.

Combustion air requirements: approximately 50 cubic feet per 1,000 Btu/h input for confined spaces with outdoor air; inadequate air causes incomplete combustion and CO.

Flue gas CO2 target is about 8–10% with 4–6% O2 for natural gas; elevated CO (over 100 ppm in flue, or any CO in room air) indicates a problem.

Gas manifold pressure for natural gas is typically 3.5 in. w.c.; LP is about 10–11 in. w.c.; always check the data plate.

Furnace efficiency: AFUE (annual fuel utilization efficiency) of 90%+ indicates a condensing furnace with a secondary heat exchanger and PVC venting.

Electric heat: 1 kW = 3,412 Btu/h; resistance heat strips are checked by amp draw and ohm readings against the nameplate.

Heat pump balance point is the outdoor temperature where heat pump capacity equals building load; below it, auxiliary or emergency heat supplements.

Defrost cycle on a heat pump reverses the refrigerant flow or stops the outdoor fan to melt frost on the outdoor coil; the system must terminate on temperature or time.

Line sizing and routing: keep suction lines short and insulated, slope horizontal suction lines toward the compressor, and avoid oil traps except where required for risers.

Evacuation: triple evacuation with nitrogen sweep to below 500 microns; a rising vacuum indicates moisture or a leak.

Leak detection order: electronic leak detector, soap bubbles, and nitrogen pressure test; never use oxygen or compressed air to pressure test refrigerant systems.

Charging methods: weigh-in for new systems and critically charged units; superheat method for fixed orifice; subcooling method for TXV systems.

Electrical troubleshooting: check voltage at the contactor, control transformer output (24 V), and thermostat continuity; a tripped high-pressure or low-pressure switch points to airflow or charge.

Diagnostic pattern: high head pressure with high subcooling = overcharge or condenser airflow restriction; low suction with high superheat = undercharge or restriction.

Airflow verification: static pressure across the blower and filter, plus temperature rise (furnace) or temperature drop (AC, typically 15–20°F) confirm proper airflow.

HVACR covers heating, ventilation, air conditioning, and refrigeration; the R distinguishes refrigeration (industrial and commercial process cooling) from comfort air conditioning.

Sensible heat changes a substance's temperature without changing phase; latent heat changes phase at constant temperature (melting, boiling, condensing).

1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW; it is the heat absorption rate of melting one ton of ice in 24 hours.

Heat always flows from higher to lower temperature; cooling does not add cold, it removes heat and moves it to a warmer location.

British thermal unit (Btu) is the heat needed to raise 1 lb of water 1°F; 1 Btu = 1.055 kJ, and 1 watt = 3.412 Btu/h.

Air composition by volume is about 78% nitrogen, 21% oxygen, and 1% other gases; comfort cooling typically targets 75°F and about 50% relative humidity.

Temperature conversions: °F = (°C × 1.8) + 32; °C = (°F − 32) ÷ 1.8; absolute scales are Rankine (°R = °F + 460) and Kelvin (K = °C + 273).

Refrigerant phase change is the core mechanism: evaporator absorbs latent heat at low pressure, condenser rejects latent heat at high pressure.

Lockout/tagout (LOTO): isolate energy, lock the disconnect, tag it, and verify zero energy before servicing; never rely on a switch position alone.

Personal protective equipment for refrigerant work includes safety glasses or goggles, gloves, long sleeves, and ventilation; liquid refrigerant contact causes frostbite.

Refrigerant cylinders are stored upright, secured, below 125°F, and never filled above 80% liquid full to allow expansion; oxygen and acetylene are stored separately.

Manifold gauge set: blue hose to low side (suction), red to high side (discharge), yellow to vacuum pump or recovery cylinder; never use hoses for both refrigerant and nitrogen without purging.

Micron gauge measures deep vacuum in microns; 1 micron = 1/25,400 mmHg; a standing vacuum below 500 microns indicates an acceptable dehydration level.

Electrical meter safety: verify CAT rating, test the meter on a known live source, and treat all conductors as energized; clamp meters read current without breaking the circuit.

Torch brazing requires a fire extinguisher, a fire watch, and nitrogen purge to prevent internal oxidation (scale) in copper lines.

Recovery, recycling, and reclamation are distinct: recovery removes refrigerant, recycling cleans it on site, reclamation restores it to ARI-700 purity at a processing facility.

Vapor-compression cycle order: compressor → condenser → metering device → evaporator → back to compressor; the compressor raises pressure and temperature.

Superheat = actual suction line temperature − evaporating (saturation) temperature; it confirms the evaporator is fully fed and protects the compressor from liquid.

Subcooling = condensing (saturation) temperature − liquid line temperature; it confirms the condenser is fully condensing and the liquid seal at the metering device.

TXV/EEV charge is set by superheat; a fixed orifice (piston) is sized by capacity, and superheat varies with load and outdoor temperature.

Pressure–temperature (PT) chart converts saturation pressure to temperature for a given refrigerant; each refrigerant has its own curve and glide (zeotropic blends).

Refrigerant types: CFCs (R-12), HCFCs (R-22), HFCs (R-410A, R-134a), and HFOs (R-1234yf); R-410A operates at roughly 50–60% higher pressure than R-22 and requires POE oil.

Evaporator superheat too high with low suction pressure suggests undercharge, a restricted metering device, or a blocked liquid line; frost on the coil indicates low airflow or low charge.

Airflow across the evaporator is typically 350–450 CFM per ton; low airflow drops suction pressure and can freeze the coil.

Gas furnace sequence: thermostat call → inducer draft motor → pressure switch proves draft → igniter → gas valve opens → flame sensor proves flame → blower delay → blower on.

Combustion air requirements: approximately 50 cubic feet per 1,000 Btu/h input for confined spaces with outdoor air; inadequate air causes incomplete combustion and CO.

Flue gas CO2 target is about 8–10% with 4–6% O2 for natural gas; elevated CO (over 100 ppm in flue, or any CO in room air) indicates a problem.

Gas manifold pressure for natural gas is typically 3.5 in. w.c.; LP is about 10–11 in. w.c.; always check the data plate.

Furnace efficiency: AFUE (annual fuel utilization efficiency) of 90%+ indicates a condensing furnace with a secondary heat exchanger and PVC venting.

Electric heat: 1 kW = 3,412 Btu/h; resistance heat strips are checked by amp draw and ohm readings against the nameplate.

Heat pump balance point is the outdoor temperature where heat pump capacity equals building load; below it, auxiliary or emergency heat supplements.

Defrost cycle on a heat pump reverses the refrigerant flow or stops the outdoor fan to melt frost on the outdoor coil; the system must terminate on temperature or time.

Line sizing and routing: keep suction lines short and insulated, slope horizontal suction lines toward the compressor, and avoid oil traps except where required for risers.

Evacuation: triple evacuation with nitrogen sweep to below 500 microns; a rising vacuum indicates moisture or a leak.

Leak detection order: electronic leak detector, soap bubbles, and nitrogen pressure test; never use oxygen or compressed air to pressure test refrigerant systems.

Charging methods: weigh-in for new systems and critically charged units; superheat method for fixed orifice; subcooling method for TXV systems.

Electrical troubleshooting: check voltage at the contactor, control transformer output (24 V), and thermostat continuity; a tripped high-pressure or low-pressure switch points to airflow or charge.

Diagnostic pattern: high head pressure with high subcooling = overcharge or condenser airflow restriction; low suction with high superheat = undercharge or restriction.

Airflow verification: static pressure across the blower and filter, plus temperature rise (furnace) or temperature drop (AC, typically 15–20°F) confirm proper airflow.