1. A technician is charging a new TXV split system by weight per the manufacturer's charging chart, then fine-tunes using subcooling. After charging, measured subcooling is 4°F, but the manufacturer specifies a target of 12°F. What should the technician do?
Cooling and Refrigeration
A.Add refrigerant to the system, since low subcooling indicates undercharge
B.Do nothing, since subcooling is not affected by charge level on TXV systems
C.Replace the TXV, since subcooling should never differ from the target
D.Recover refrigerant to reduce the charge, since low subcooling indicates overcharge
Show answerAnswer
A. Add refrigerant to the system, since low subcooling indicates undercharge
On TXV systems, subcooling is the primary charging indicator. A subcooling reading below the target (4°F vs. 12°F target) indicates insufficient liquid refrigerant backed up in the condenser, meaning the system is undercharged, so refrigerant should be added until target subcooling is reached.
2. A technician measures a run capacitor rated 35 µF (±6% tolerance) and gets a reading of 28 µF on a capacitance meter. What should the technician conclude?
Controls, Electrical and Safety
A.The low reading means the meter, not the capacitor, is defective
B.The reading indicates the capacitor is oversized and should be downsized
C.The capacitor is weak and out of tolerance, and should be replaced
D.The capacitor is within tolerance and can remain in service
Show answerAnswer
C. The capacitor is weak and out of tolerance, and should be replaced
A 35 µF capacitor with ±6% tolerance has an acceptable range of about 32.9 to 37.1 µF. A reading of 28 µF is well below this range, indicating the capacitor has degraded internally and lost capacitance, which reduces motor starting/running torque and should be replaced.
3. A commercial office space measuring 2,000 sq ft has a design occupancy of 20 people. Using the ASHRAE 62.1 Ventilation Rate Procedure default rates of 5 CFM per person plus 0.06 CFM per square foot for office space, what is the minimum required outdoor air ventilation rate?
Ventilation and Air Distribution
A.120 CFM
B.100 CFM
C.220 CFM
D.340 CFM
Show answerAnswer
C. 220 CFM
ASHRAE 62.1 combines a people-based component and an area-based component: (5 CFM × 20 people) + (0.06 CFM/sq ft × 2,000 sq ft) = 100 CFM + 120 CFM = 220 CFM total outdoor air.
4. A Manual D duct design specifies a total system airflow of 1,200 CFM distributed among five supply branches. Four branches are measured after installation and deliver 220, 180, 260, and 240 CFM respectively. Assuming no duct leakage, what CFM must the fifth branch deliver to match the design total?
Planning and Layout
A.275 CFM
B.320 CFM
C.300 CFM
D.240 CFM
Show answerAnswer
C. 300 CFM
Sum the four known branches: 220 + 180 + 260 + 240 = 900 CFM. Subtract from the total system design airflow: 1,200 − 900 = 300 CFM. This confirms the fifth branch must deliver 300 CFM for the system to balance to the design total.
5. Per the Uniform Mechanical Code, a furnace installed in a small utility closet with a volume of 40 cubic feet and no direct free communication with additional adjoining rooms is classified as being in which type of space?
Heating Systems
A.Category IV space
B.Direct-vent space
C.Confined space
D.Unconfined space
Show answerAnswer
C. Confined space
A confined space is defined as one with less than 50 cubic feet per 1,000 Btu/h of total input of all appliances installed in the space. A small 40-cubic-foot closet clearly falls under this classification, requiring engineered combustion air provisions such as ducted openings or outdoor air connections.
6. A mechanical blueprint includes an equipment schedule table listing unit tag 'FAU-1' with a specified airflow of 1,600 CFM and a rated output of 80,000 Btu/hr. Before beginning rough-in, where should a technician look on the plans to confirm this equipment information?
Planning and Layout
A.The electrical panel schedule
B.The architectural elevation drawings
C.The structural framing plan
D.The mechanical equipment schedule
Show answerAnswer
D. The mechanical equipment schedule
Mechanical equipment schedules are tables on the blueprints (often on the mechanical sheet) that list each piece of equipment by tag along with its specifications such as CFM, Btu/hr rating, voltage, and model number. Technicians reference this schedule to confirm design intent before installation.
7. On a residential split system equipped with a thermostatic expansion valve (TXV), where is the filter drier normally installed?
Cooling and Refrigeration
A.In the suction line, between the evaporator and the compressor
B.In the discharge line, between the compressor and the condenser
C.In the liquid line, between the condenser outlet and the metering device
D.Inside the suction line accumulator housing
Show answerAnswer
C. In the liquid line, between the condenser outlet and the metering device
The filter drier is installed in the liquid line so it can remove moisture, acid, and debris from the liquid refrigerant before it reaches the fine metering orifice of the TXV, protecting it from clogging and preventing moisture-related acid formation.
8. What is the primary purpose of a start capacitor in a single-phase motor circuit, and when is it typically removed from the circuit?
Controls, Electrical and Safety
A.It provides extra starting torque during startup and is switched out of the circuit once the motor reaches speed
B.It protects the motor windings from overheating and stays in the circuit at all times
C.It filters electrical noise for the thermostat and is unrelated to motor torque
D.It smooths voltage ripple continuously and remains energized while the motor runs
Show answerAnswer
A. It provides extra starting torque during startup and is switched out of the circuit once the motor reaches speed
A start capacitor is wired in series with the start winding to create a phase shift that boosts starting torque. Once the motor reaches roughly 75% of its rated speed, a relay (potential or current relay) opens and disconnects the start capacitor, since it is not designed for continuous duty and would overheat.
9. Per California Title 24/CALGreen requirements, a bathroom exhaust fan intended for continuous whole-house ventilation operation must have a maximum sound rating, when tested at 0.25 in. w.c., of no more than how many sones?
Ventilation and Air Distribution
A.3.0 sones
B.0.5 sone
C.1.0 sone
D.5.0 sones
Show answerAnswer
C. 1.0 sone
CALGreen and ASHRAE 62.2 require exhaust fans used for continuous whole-house ventilation to be rated at 1.0 sone or less to minimize occupant annoyance from continuous operation, encouraging occupants to leave the fan running.
11. A technician performs a Title 24 duct leakage test using a duct blaster. Before pressurizing the duct system to 25 Pascals, the technician seals all supply and return registers with tape. What does this test procedure measure?
Ventilation and Air Distribution
A.Static pressure drop across the air handler
B.Design airflow at each individual register
C.Total duct leakage (leakage to both inside and outside conditioned space)
D.Leakage to outside only, using the pressure-pan method
Show answerAnswer
C. Total duct leakage (leakage to both inside and outside conditioned space)
Sealing all registers isolates the duct system entirely, so the duct blaster fan flow needed to reach 25 Pa measures all leakage from the ducts, whether it leaks into conditioned space or outside — this is the 'Total Leakage' test. The 'Leakage to Outside' test instead uses a blower door in conjunction with the duct blaster and does NOT seal the registers, canceling out leaks to the inside.
12. A Manual T register selection process determines a supply diffuser has a rated throw of 12 feet at a terminal velocity of 50 fpm. The diffuser is installed in a room where the opposite wall is 18 feet away. What is the most likely consequence of this selection?
Planning and Layout
A.Increasing duct static pressure will automatically extend the register's throw to 18 feet
B.Supply air will lose velocity before reaching the far wall, resulting in poor air mixing and possible stagnant zones
C.Throw ratings are irrelevant once terminal velocity drops below 100 fpm
D.The register throw is more than sufficient to reach the opposite wall
Show answerAnswer
B. Supply air will lose velocity before reaching the far wall, resulting in poor air mixing and possible stagnant zones
Since the diffuser's rated throw of 12 feet falls short of the 18-foot distance to the opposite wall, the supply air stream will decelerate and drop before adequately mixing with room air near that wall, creating comfort complaints and temperature stratification.
13. A duct system operating at 1,200 CFM produces 0.60 in. w.c. of total external static pressure. If airflow is increased to 1,400 CFM through the same unchanged duct system, what is the new approximate static pressure (fan affinity law: pressure varies with the square of the CFM ratio)?
Ventilation and Air Distribution
A.0.60 in. w.c.
B.0.70 in. w.c.
C.0.82 in. w.c.
D.1.02 in. w.c.
Show answerAnswer
C. 0.82 in. w.c.
Ratio = 1400/1200 = 1.167. Squaring gives 1.361. New pressure = 0.60 × 1.361 ≈ 0.82 in. w.c. Static pressure rises with the square of airflow when the duct system is unchanged.
14. In a heat pump system, what component allows the unit to switch between heating and cooling modes by redirecting refrigerant flow?
Heating Systems
A.Thermostatic expansion valve
B.Bi-flow filter drier
C.Suction line accumulator
D.Reversing valve
Show answerAnswer
D. Reversing valve
The reversing valve, controlled by a solenoid, changes the direction of refrigerant flow between the indoor and outdoor coils, allowing the same coils to function as either evaporator or condenser depending on whether the system is in heating or cooling mode.
15. A homeowner asks what type of EPA Section 608 certification is required to service a small window air conditioner containing less than 5 pounds of refrigerant that will be repaired without removing the sealed system.
Cooling and Refrigeration
A.Type III certification
B.Universal certification
C.Type II certification
D.Type I certification
Show answerAnswer
D. Type I certification
Type I certification under EPA Section 608 covers technicians who service small appliances, defined as factory-sealed systems containing 5 pounds or less of refrigerant, such as window units and small refrigerators.
16. Per California Title 24 requirements for a newly installed residential duct system, what is the maximum allowable total duct leakage as verified by a HERS rater's diagnostic test?
Ventilation and Air Distribution
A.15% of total fan airflow
B.2% of total fan airflow
C.5% of total fan airflow
D.25% of total fan airflow
Show answerAnswer
C. 5% of total fan airflow
Title 24 requires new duct systems to be tested and verified with total leakage not exceeding 5% of the air handler's design airflow, ensuring energy efficiency and proper delivered CFM to conditioned spaces.
17. A 24-volt, 40 VA control transformer powers a thermostat and relay circuit. What is the maximum continuous current this transformer can safely supply?
Controls, Electrical and Safety
A.24 amps
B.1.67 amps
C.0.6 amp
D.40 amps
Show answerAnswer
B. 1.67 amps
VA (volt-amps) equals voltage multiplied by current, so current equals VA divided by voltage: 40 VA ÷ 24 V = 1.67 amps. Loading the secondary beyond this value will overheat the transformer and can trip its internal overcurrent protection or cause premature failure.
18. A Manual D duct design must deliver a total system airflow of 1,500 CFM to match the equipment's rated output. A specific bedroom has a calculated heat load of 3,000 Btu/hr out of a whole-house total load of 45,000 Btu/hr. Using the proportional load-based method for branch duct airflow allocation, how much airflow should be routed to this bedroom's branch duct?
Planning and Layout
A.75 CFM
B.200 CFM
C.100 CFM
D.150 CFM
Show answerAnswer
C. 100 CFM
Room CFM = (Room Load ÷ Total Load) × Total System CFM = (3,000 ÷ 45,000) × 1,500 = 0.0667 × 1,500 = 100 CFM.
19. A technician is charging a system using R-407C, a zeotropic refrigerant blend. Why must this refrigerant be added to the system as a liquid rather than a vapor?
Cooling and Refrigeration
A.R-407C exists only in liquid form at room temperature and has no vapor phase
B.Charging as a vapor could cause fractionation, changing the blend's composition and altering system performance
C.Liquid charging is simply faster and more convenient for the technician
D.Vapor charging of any refrigerant is prohibited under federal law
Show answerAnswer
B. Charging as a vapor could cause fractionation, changing the blend's composition and altering system performance
R-407C is a zeotropic blend composed of multiple refrigerant components with different boiling points, creating temperature glide. If charged as a vapor, the more volatile components boil off first, changing the blend ratio (fractionation) and shifting the refrigerant's performance characteristics. Charging as a liquid preserves the intended blend composition.
20. A technician is using a manufacturer's target superheat chart to charge a fixed-orifice metering device system. Which two measurements are required to determine the correct target superheat value from the chart?
Cooling and Refrigeration
A.Outdoor dry-bulb temperature and indoor (return air) wet-bulb temperature
B.Discharge line pressure and compressor amperage draw
C.Indoor dry-bulb temperature and outdoor wet-bulb temperature
D.Suction line pressure and liquid line temperature
Show answerAnswer
A. Outdoor dry-bulb temperature and indoor (return air) wet-bulb temperature
Target superheat charts for fixed-orifice systems require two inputs: the outdoor ambient dry-bulb temperature and the indoor return air wet-bulb temperature (which reflects indoor humidity load). These two values are cross-referenced on the manufacturer's chart to find the correct target superheat for charging.
21. A technician is recovering refrigerant from a residential system into a DOT-approved recovery cylinder. To prevent hydrostatic overpressure and cylinder rupture, filling should stop at approximately what percentage of the cylinder's rated weight capacity?
Cooling and Refrigeration
A.100%
B.80%
C.90%
D.60%
Show answerAnswer
B. 80%
DOT regulations and industry standards require recovery cylinders to be filled to no more than 80% of their rated capacity by weight, leaving vapor space for thermal expansion of the liquid refrigerant and preventing hydrostatic rupture.
22. A duct system must deliver a sensible cooling load of 24,000 Btu/hr with a supply air temperature drop (ΔT) of 20°F. Using the standard sensible heat formula, what CFM is required?
Planning and Layout
A.1000 CFM
B.1200 CFM
C.1333 CFM
D.1111 CFM
Show answerAnswer
D. 1111 CFM
The sensible heat formula is CFM = Btu/hr ÷ (1.08 × ΔT). Substituting: 24,000 ÷ (1.08 × 20) = 24,000 ÷ 21.6 = 1,111 CFM.
23. A technician must perform diagnostic work on an energized 480-volt panel where de-energization is not feasible due to critical operations. Per Cal/OSHA electrical safety requirements, what must be used to protect the technician?
Controls, Electrical and Safety
A.Appropriate arc-rated PPE and insulated tools rated for the voltage and incident energy level
B.A second technician standing by with a fire extinguisher
C.A rubber floor mat with no other protective equipment
D.Standard leather work gloves and safety glasses only
Show answerAnswer
A. Appropriate arc-rated PPE and insulated tools rated for the voltage and incident energy level
Cal/OSHA requires that when work on energized equipment cannot be avoided, technicians must use arc-rated PPE and insulated tools rated for the specific voltage and calculated incident energy exposure, following an established energized work permit process. Leather gloves alone, a mat by itself, or a bystander with an extinguisher do not meet the required protective standard for live electrical work.
24. A new 96% AFUE condensing furnace is installed. Which venting material is code-approved for its Category IV flue gas venting?
Heating Systems
A.Uninsulated aluminum flex duct
B.Single-wall galvanized steel
C.Type B double-wall vent
D.Schedule 40 PVC
Show answerAnswer
D. Schedule 40 PVC
Category IV condensing furnaces produce acidic, cool flue gas condensate under positive pressure, requiring corrosion-resistant plastic venting such as PVC, CPVC, or polypropylene as listed by the manufacturer.
25. A hydronic heating system develops persistent air bubbles in the baseboard radiators, causing gurgling noises and reduced heat output. Which component is designed to remove entrained air from the system?
Heating Systems
A.Air separator
B.Aquastat
C.Backflow preventer
D.Zone valve
Show answerAnswer
A. Air separator
An air separator, often installed near the boiler supply and paired with the expansion tank, collects and vents entrained air bubbles from the circulating water, preventing airlock and noise in the piping and terminal units.
On TXV-equipped systems, technicians verify and adjust refrigerant charge primarily using subcooling measurements compared against manufacturer-specified targets.
Low subcooling relative to target = undercharge, add refrigerant
High subcooling relative to target = overcharge, recover refrigerant
TXV systems use subcooling as primary charge check (not superheat)
Commercial ventilation requirements combine a per-person outdoor air rate and a per-area outdoor air rate, both of which must be added together to determine minimum outdoor air CFM.
A confined space has less than 50 cubic feet of volume per 1,000 Btu/h of appliance input; an unconfined space has more, allowing natural infiltration for combustion air.
Rule of thumb: 50 cu ft per 1,000 Btu/h input
Confined spaces need engineered combustion air openings
Determines whether ducted or direct openings are required
The filter drier is installed in the liquid line ahead of the metering device to remove moisture, acid, and debris before refrigerant reaches the TXV or orifice.
Protects TXV/orifice from clogging
Removes moisture to prevent acid formation
Should be replaced after compressor burnout (suction line drier used temporarily)
A start capacitor provides a large capacitance boost to increase starting torque in single-phase motors and is disconnected by a relay once the motor reaches running speed.
Wired in series with the start winding
Disconnected by potential or current relay near 75% speed
Not rated for continuous duty, unlike a run capacitor
Total Leakage testing seals all registers and measures all duct leaks; Leakage to Outside testing leaves registers open and uses a blower door to isolate only leaks that escape the building envelope.
Total leakage test: registers sealed, duct blaster only
Leakage to outside test: registers open, blower door + duct blaster together
Title 24 compliance often requires leakage to outside ≤ 6% of fan flow
Manual T evaluates air distribution devices by matching rated throw (distance air travels before reaching terminal velocity) to room dimensions for proper air mixing.
Terminal velocity is typically defined at 50 fpm
Throw shorter than room depth causes poor mixing and comfort issues
Register selection must match both CFM and room geometry
In Manual D duct design, each room's branch airflow is allocated proportionally to its share of the whole-house heat load relative to total system airflow.
Room CFM = (Room Load / Total Load) × Total System CFM
Ensures each space receives conditioning matched to its load
Prevents over- or under-conditioning individual rooms
Zeotropic refrigerant blends (like R-407C) contain components with different boiling points and must be charged as a liquid to prevent the mixture from separating (fractionating) during charging.
Zeotropic blends exhibit temperature glide
Vapor charging removes lighter components first, altering blend ratio
Near-azeotropic blends like R-410A have minimal glide but manufacturers still recommend liquid charging
A manufacturer-provided chart used to determine correct superheat for fixed-orifice systems based on outdoor dry-bulb temperature and indoor return air wet-bulb temperature.
Only used for fixed-orifice (non-TXV) systems
Indoor wet-bulb reflects humidity load on the evaporator
TXV systems use subcooling charging method instead
Recovery cylinders must never be filled beyond 80% of their rated weight capacity to allow for liquid thermal expansion and prevent overpressure rupture.
Applies to all DOT-approved refrigerant recovery cylinders
Leaves 20% vapor space for expansion
Overfilling can cause dangerous hydrostatic pressure buildup
Cal/OSHA requires arc-rated PPE and insulated tools rated for the specific voltage and incident energy when work on energized equipment cannot be de-energized.
Energized work requires a documented justification/permit
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