CORE: Electrical Theory
Not publishedof exam
CORE: Refrigeration Theory
Not publishedof exam
Combustion Analysis & Gas Heat
Not publishedof exam
Electric Heat
Not publishedof exam
Heat Pumps (Installer & Service)
Not publishedof exam
Residential Air Conditioning
Not publishedof exam
Light Commercial Air Conditioning
Not publishedof exam
Light Commercial Refrigeration
Not publishedof exam
Residential & Light Commercial Hydronic Heat
Not publishedof exam
Quick Facts
- Body
- HVAC Excellence (ESCO Group)
- Level
- Professional Level Technician
- Exams
- 10 separate written exams
- Questions
- 100 per exam
- Format
- Closed-book written exam
- Prerequisite
- CORE exam required first
- Experience
- 2 years verified field work
- Pass score
- Not published
- Time limit
- Not published
- Fee
- Not published
- Validity
- Not published
Electrical Theory
- Ohm's Law
- E = I x R
- Watt's Law
- P = E x I
- Series Circuit
- One current path only
- Parallel Circuit
- Same voltage, split current
- kVA vs kW
- Apparent power vs real
- Ladder Diagram
- Numbered rungs, standard symbols
Electrical Components
- Relay
- Light-duty control switch
- Contactor
- Heavy-duty load switch
- Motor Starter
- Contactor plus overload protection
- Run Capacitor
- Continuous phase-shift duty
- Start Capacitor
- Momentary extra starting torque
- Control Transformer
- Steps line voltage to 24V
- PSC Motor
- Permanent split-capacitor design
Refrigeration Cycle Order
Compress, Condense, Meter, Evaporate
Compressor raises pressureCondenser rejects heatMetering device drops pressureEvaporator absorbs heat
Superheat vs Subcooling
Superheat
- Checks fixed-orifice charge
- Vapor above boiling point
- Measured on suction line
Subcooling
- Checks TXV charge
- Liquid below condensing point
- Measured on liquid line
Vapor rise vs liquid drop
Charging Method Picker
- TXV system→Check subcooling(Target from mfr chart)
- Fixed orifice system→Check superheat(Target from mfr chart)
- Heat pump heating mode→Manufacturer's heating chart(Not superheat or subcool)
- No chart available→Weigh in nameplate charge(Plus line-length adjustment)
- Long line set run→Add per mfr adjustment(Ounces per extra foot)
- Charge totally unknown→Recover then weigh in(Most reliable method)
Refrigeration Cycle
- Compressor
- Raises pressure and temperature
- Condenser
- Rejects heat, condenses vapor
- Metering Device
- Drops pressure, meters flow
- Evaporator
- Absorbs heat, boils refrigerant
- High Side
- Compressor outlet to metering device
- Low Side
- Metering device to compressor inlet
- Latent Heat
- Heat with no temperature change
Refrigerant Safety Classes
A1 safest, A3 most flammable
A1 means R-410A, no flameA2L means R-32 or R-454BA3 means R-290, propaneB class means higher toxicity
Refrigerant Safety
- A1 Class
- Lower toxicity, no flame
- A2L Class
- Lower toxicity, mild flame
- A3 Class
- Lower toxicity, high flame
- R-410A
- A1 refrigerant, common R-22 replacement
- R-32 / R-454B
- A2L, replacing R-410A
- R-290
- Propane; A3, highly flammable
- EPA Section 608
- Recovery certification required
Gas Furnace Start Sequence
Inducer, Switch, Ignite, Valve, Flame, Blower
Inducer starts the draftSwitch proves that draftIgniter or pilot firesValve opens the fuelFlame sensor proves fireBlower delivers warm air
Standing Pilot vs Hot Surface Ignition
Standing Pilot
- Burns continuously, always lit
- Thermocouple proves the flame
Hot Surface Ignition
- Electric igniter, no pilot
- Fires only on each call
Continuous flame vs on-demand
Gas Heat Fault Picker
- Inducer will not start→Check board and wiring(First sequence step)
- Inducer runs, no ignition→Check pressure switch(Proves adequate draft)
- Igniter will not glow→Check igniter resistance(Replace if open)
- Flame lights then drops→Check flame sensor signal(Weak microamp reading)
- Sooty, yellow flame→Check primary air setting(Risk of CO)
- Nuisance limit trips→Check airflow and filter(Not a gas fault)
Combustion Analysis
- Primary Air
- Mixes with fuel first
- Secondary Air
- Completes combustion at flame
- Excess Air
- Extra air beyond ideal
- Carbon Monoxide
- Colorless, toxic, incomplete combustion
- Draft
- Moves flue gas outward
- Stack Temperature
- Flue gas exit reading
- Combustion Efficiency
- Calculated from O2 and CO2
Manifold Pressure Memory Line
Natural gas 3.5, propane about 10
Natural gas runs about 3.5 wcPropane runs about 10 wcAlways confirm the nameplate valueWrong pressure misfires the burner
Category I vs Category IV Venting
Category I
- Negative pressure, non-condensing
- Conventional furnace venting
Category IV
- Positive pressure, condensing
- Needs sealed plastic vent
Natural draft vs fan-forced vent
Combustion Analyzer Reading Picker
- CO reading is high→Check burner and exchanger(Incomplete combustion sign)
- O2 reading is high→Check for excess air(Draft or setting)
- Stack temp too high→Check for over-firing(Or a fouled exchanger)
- Draft reading is weak→Check vent and exhaust fans(Depressurization risk)
Gas Heat Components
- Thermocouple
- About 25-30 mV signal
- Hot Surface Ignition
- Electric igniter, no pilot
- Flame Rectification
- Flame conducts AC to DC
- Manifold Pressure
- About 3.5 in wc natural
- LP Manifold Pressure
- About 10 in wc propane
- Limit Switch
- Opens circuit on overheat
- Category IV Venting
- Positive pressure, condensing, sealed
Electric Heat
- Heat Sequencer
- Stages elements on then off
- Fusible Link
- One-time backup safety device
- Limit Switch
- Auto-reset overheat protection
- kW to Btu/h
- Multiply kW by 3412
- Amp Draw
- Watts divided by volts
- CFM Formula
- Btu/h / (1.08 x dT)
Auxiliary vs Emergency Heat
Auxiliary Heat
- Stages on automatically
- Runs together with compressor
Emergency Heat
- Manual thermostat setting
- Locks the compressor out
Automatic help vs manual override
Heat Pump Mode Fault Picker
- Heats on a cool call→Check O and B wiring(Wrong terminal energized)
- Defrost never starts→Check timer or sensor(Time-temp or demand type)
- Reversing valve will not shift→Check for pressure difference(Needs compressor running)
- Below the balance point→Confirm aux heat stages(Compressor alone insufficient)
- Compressor short-cycles when cold→Check crankcase heater(Oil dilution risk)
Heat Pump Fundamentals
- Reversing Valve
- Swaps coil roles by mode
- Balance Point
- Heat loss equals HP output
- Defrost Cycle
- Briefly cools, melts coil frost
- Crankcase Heater
- Prevents refrigerant oil migration
- Auxiliary Heat
- Automatic backup heat stage
- Emergency Heat
- Manual setting, compressor locked out
- O Terminal
- Energizes valve in cooling
- B Terminal
- Energizes valve in heating
O Terminal vs B Terminal
O Terminal
- Energizes valve in cooling
- Most manufacturers' default wiring
B Terminal
- Energizes valve in heating
- Used by Rheem and Ruud
Cooling-energized vs heating-energized valve
Heat Pump Service
- Demand Defrost
- Sensor-triggered, not fixed timer
- Time-Temp Defrost
- Fixed timer plus coil sensor
- Line Set Sizing
- From capacity and length charts
- Charging Method
- Weigh in nameplate charge
- Heating-Mode Charge
- Use manufacturer's heating chart
SEER2 Minimum Memory Line
13.4 North, 14.3 South split AC
North region needs 13.4 SEER2Southeast and Southwest need 14.3Split heat pumps need 14.3M1 test raised static pressure
TXV vs Fixed Orifice
TXV
- Sensing bulb feedback control
- Holds a target superheat
- Handles changing loads well
Fixed Orifice
- No moving parts inside
- Flow follows pressure only
- Needs an exact charge
Modulates flow vs fixed flow
Residential Air Conditioning
- TXV
- Modulates flow, holds superheat
- Fixed Orifice
- No moving parts inside
- SEER2
- 2023-plus efficiency test metric
- SEER2 Minimum
- 13.4 North, 14.3 South
- Static Pressure
- Blower resistance, measured in wc
- Nitrogen Purge
- Prevents copper oxide scale
- Sensible vs Latent
- Temperature drop vs moisture removal
Light Commercial Air Conditioning
- Rooftop Unit
- Self-contained, curb-mounted package
- Economizer
- Free cooling with outdoor air
- Compressor Staging
- Multiple compressors match load
- Minimum OA Damper
- Set and measured at commissioning
- Draw-Through Drain
- Needs a deep trap depth
- Float Switch
- Shuts unit down on overflow
EPR vs CPR Valve
EPR Valve
- At the evaporator outlet
- Limits low coil temperature
CPR Valve
- At the compressor inlet
- Limits high suction pressure
Evaporator side vs compressor side
Light Commercial Refrigeration
- EPR Valve
- Limits low evaporator pressure
- CPR Valve
- Limits high suction pressure
- Head Pressure Control
- Holds pressure up in cold
- Off-Cycle Defrost
- Coolers only, above freezing
- Hot Gas Defrost
- Freezers, below freezing point
- Pump-Down Cycle
- Stores charge in condenser
Sweating vs Frosting
Sweating
- Humidity or a bad gasket
- Surface condensation, not ice
Frosting
- Low airflow or low charge
- Ice buildup on the coil
Humidity issue vs refrigerant issue
Hydronic Heat
- Aquastat
- Senses water, controls burner
- Circulator Pump
- Moves water around closed loop
- Expansion Tank
- Absorbs heated water expansion
- Fill Pressure
- About 12 psi when cold
- Relief Valve
- Opens near 30 psi
- Zone Valve
- Opens one zone per call
Common Traps
Superheat vs Subcooling Use
Superheat checks fixed orifice ≠ Subcooling checks TXV charge
EPR vs CPR Location
EPR limits evaporator pressure ≠ CPR limits compressor suction
Auxiliary vs Emergency Heat
Auxiliary stages automatically ≠ Emergency locks out compressor
O vs B Terminal
O energizes cooling mode ≠ B energizes heating mode
Sweating vs Frosting Cause
Sweating means a humidity issue ≠ Frosting means airflow or charge
Category I vs IV Vent
Category I is negative draft ≠ Category IV is positive, sealed
Standing Pilot vs HSI
Standing pilot burns continuously ≠ HSI ignites only on call
Last Minute
- 1.CORE exam required before others
- 2.Two years field experience required
- 3.Superheat checks fixed-orifice refrigerant charge
- 4.Subcooling checks TXV refrigerant charge
- 5.Natural gas manifold: about 3.5 wc
- 6.LP manifold pressure: about 10 wc
- 7.SEER2 minimum: 13.4 or 14.3
- 8.kW times 3412 equals Btu/h
- 9.O terminal cools; B terminal heats
- 10.Hydronic fill 12 psi; relief 30
- 11.HVAC Excellence publishes no domain weights
- 12.Master Specialist needs hands-on testing too
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