Tennessee CMC Plumbing and HVAC Contractor Examination

One ton of refrigeration is defined as a heat-removal rate of:

• A6,000 Btu/h
• B12,000 Btu/h
• C24,000 Btu/h
• D288,000 Btu/h

Sensible heat is the heat that:

• AChanges the moisture content of air without changing dry-bulb temperature
• BChanges dry-bulb temperature without changing moisture content
• CIs rejected only at the cooling tower
• DExists only inside the refrigerant circuit

Superheat is the temperature of refrigerant vapor above:

• AThe outdoor dry-bulb temperature
• BThe saturation temperature that corresponds to the measured suction pressure
• CThe condensing temperature on the high side
• DThe oil flash point

The three modes of heat transfer that appear in HVAC load and equipment work are:

• ACompression, expansion, and evaporation
• BConduction, convection, and radiation
• CSensible, latent, and enthalpy only
• DForced, induced, and natural draft

On a psychrometric chart, wet-bulb temperature is most directly used to determine:

• ADuct friction rate in inches of water column
• BThe enthalpy and moisture content of moist air
• CGas-pipe capacity in cubic feet per hour
• DSprinkler K-factor

The specific gravity used in the 2021 International Fuel Gas Code natural-gas pipe-sizing tables is:

• A0.15
• B0.60
• C1.00
• D1.50

The Tennessee Full Mechanical (CMC) examination references which edition of the International Mechanical Code?

• A2015 IMC
• B2018 IMC
• C2021 IMC
• D2024 IMC

Where the 2021 IMC and the appliance manufacturer's installation instructions conflict, the installer shall follow:

• AThe manufacturer's instructions only, because listed equipment always overrides the code
• BThe more restrictive of the two requirements that still keeps the listing intact
• CWhichever document is newer, regardless of restrictiveness
• DLocal custom even if both documents are more restrictive

Per IMC 2021 Section 306.1, the level working space in front of the control side of an appliance shall be not less than:

• A18 inches deep by 18 inches wide
• B24 inches deep by 24 inches wide
• C30 inches deep by 30 inches wide
• D48 inches deep by 36 inches wide

IMC 2021 Section 307.2.1 requires cooling-coil condensate piping to slope toward the approved disposal point at not less than:

• A1/16 inch per foot
• B1/8 inch per foot (1-percent slope)
• C1/2 inch per foot
• D1 inch per foot

Appliances regulated by the IMC shall be:

• AField-fabricated from unlisted parts whenever that is cheaper
• BListed and labeled for the application and installed to the listing
• CAccepted if they resemble a listed model
• DExempt from listing when installed outdoors

Where a gas appliance does not include a factory sediment trap, IFGC 2021 Section 408.4 requires a sediment trap:

• AUpstream of the meter only
• BDownstream of the appliance shutoff valve, as close to the appliance inlet as practical
• CAnywhere on the house manifold
• DOnly on CSST systems

Per IFGC 2021 Section 411.1.3.1, a listed gas appliance connector shall have an overall length not greater than:

• A3 feet
• B6 feet
• C10 feet
• D15 feet

Traditional (non-arc-resistant) CSST gas piping shall be bonded to the electrical-service grounding-electrode system with a jumper not smaller than:

• A12 AWG copper
• B10 AWG copper
• C6 AWG copper
• D2 AWG aluminum only

Using IFGC 2021 Table 402.4(2) (Schedule 40 metallic pipe, natural gas, inlet less than 2 psi, 0.5-inch w.c. drop, specific gravity 0.60), what is the smallest pipe that can supply an 80,000 Btu/h appliance 60 feet of developed length from the point of delivery? At 60 feet the table capacities are 65 cfh for 1/2 inch, 137 cfh for 3/4 inch, and 257 cfh for 1 inch. Assume 1,000 Btu per cubic foot.

• A1/2 inch
• B3/4 inch
• C1 inch
• D1-1/4 inch

A natural-gas system is sized by the IFGC longest-length method. The most remote outlet is 60 feet from the meter. A branch serving only a 200,000 Btu/h furnace is taken off that system. Using Table 402.4(2) capacities at 60 feet (65 / 137 / 257 / 528 cfh for 1/2, 3/4, 1, and 1-1/4 inch) and 1,000 Btu/ft3 gas, the furnace branch shall be at least:

• A1/2 inch
• B3/4 inch
• C1 inch
• D2 inch

Under IFGC 2021 Section 406.4.1, the gas-piping pressure test shall be not less than 1-1/2 times the proposed maximum working pressure and not less than:

• A1 psig for 1 minute
• B3 psig, irrespective of design pressure
• C10 psig for every system, with no exceptions
• DWorking pressure only, with no multiplier

Using the IFGC standard-method indoor combustion-air volume of 50 cubic feet per 1,000 Btu/h, what minimum room volume is required for a 100,000 Btu/h appliance? A 20 ft by 20 ft by 8 ft room contains 3,200 ft3.

• A2,000 cubic feet; the 3,200 ft3 room is adequate by itself
• B5,000 cubic feet; the 3,200 ft3 room needs additional indoor or outdoor air
• C10,000 cubic feet for any gas appliance
• D50 cubic feet total, regardless of input

Which appliances are exempt from the IFGC 408.4 sediment-trap requirement?

• AFurnaces, boilers, and water heaters
• BIlluminating appliances, ranges, clothes dryers, decorative vented appliances in vented f…
• CAll CSST-connected appliances
• DAny appliance under 40,000 Btu/h

Before opening an electrical disconnect and servicing a rooftop unit, the mechanic shall:

• ARely on the thermostat being set to off
• BApply lockout/tagout so the equipment cannot be re-energized while work is in progress
• CRemove the unit nameplate to keep others from starting it
• DLeave the disconnect on so controls can be tested live

The principal inhalation hazard when a large refrigerant charge is released into an unventilated machinery room is:

• AOxygen displacement and asphyxiation
• BFood poisoning
• CSunburn
• DElevated carbon monoxide from the refrigerant itself

To pressure-leak-test an R-410A circuit after recovery, the safe inert gas is:

• AOxygen
• BCompressed air from an oil-lubed shop compressor
• CDry nitrogen, with the system first reduced to 0 psig so residual refrigerant is not vent…
• DAcetylene

On a construction site, OSHA generally requires fall protection when a worker is exposed to a fall of:

• A2 feet or more
• B4 feet or more in general industry, and 6 feet or more in construction
• C20 feet or more only
• DNo height limit if a hard hat is worn

Polyolester (POE) oil used with HFC refrigerants such as R-410A is best described as:

• AHarmless skin cream that needs no PPE
• BHygroscopic and irritating; gloves and eye protection are required, and containers must s…
• CCompletely compatible with residual mineral oil, so flushing is never required
• DA water-based lubricant

A walk-in chiller barrel pit with limited entry and exit and a potential oxygen-deficient atmosphere is treated as:

• AAn ordinary mechanical closet with no extra precautions
• BA permit-required confined space until atmospheric testing and a written program say othe…
• CA space that only needs a flashlight
• DExempt from OSHA because it is outdoors

Intentionally venting fluorinated refrigerant to atmosphere during service is:

• AAllowed if the charge is under 5 pounds
• BProhibited by the Clean Air Act Section 608, with narrow exceptions such as de minimis re…
• CRequired in order to measure superheat
• DAllowed for R-410A because it has zero ozone-depletion potential

A reusable refrigerant recovery cylinder should be filled to no more than about 80 percent of its water capacity primarily because:

• AThe remaining 20 percent is reserved for oil only
• BLiquid expansion with temperature rise can over-pressure a 100-percent-full cylinder
• CEPA requires cylinders to be stored empty
• DThe pressure relief valve will not open unless the cylinder is 80 percent full

A space thermostat used for comfort control should be mounted:

• AOn an exterior wall in direct sun so it 'sees' the weather
• BOn an interior wall, out of supply-air streams, about 5 feet above the floor in a represe…
• CInside the supply duct
• DOn the furnace vestibule door

On an air-source heat pump, the reversing valve's function is to:

• AMeter liquid refrigerant into the evaporator like a TXV
• BRedirect discharge gas so the indoor coil is either the condenser (heating) or the evapor…
• CBypass the compressor during defrost only
• DRelieve high-side pressure to the suction line continuously

An air-side economizer reduces mechanical cooling energy by:

• AAlways recirculating 100 percent return air
• BUsing outdoor air for cooling when outdoor enthalpy or dry-bulb is favorable
• COvercharging the circuit so head pressure stays high
• DShutting off ventilation whenever the building is occupied

A compressor high-pressure cut-out opens the control circuit when:

• ASuction pressure falls below the freeze-protection set point
• BDischarge pressure exceeds the switch set point, typically from dirty condenser, failed f…
• CThe thermostat is satisfied
• DOil pressure is normal

NEC 440.14 requires a disconnecting means for an air-conditioning unit to be:

• ALocated anywhere in the building as long as it is labeled
• BWithin sight from and readily accessible at the equipment, unless an accepted lockable ex…
• COmitted when the unit has a thermostat
• DInstalled only at the utility transformer

Conductor and overload sizing for a hermetic compressor shall be based primarily on:

• AA generic 1-horsepower-per-ton rule
• BThe equipment nameplate rated-load current (RLA) or branch-circuit selection current
• CThe largest fuse the disconnect will physically accept
• DThe indoor-fan horsepower only

Dual-element time-delay fuses are preferred on motor and compressor circuits because they:

• AOpen instantly on the first cycle of inrush so the motor never starts
• BTolerate locked-rotor inrush for a few seconds but still open on a sustained overload or…
• CReplace the equipment grounding conductor
• DIncrease the nameplate RLA

A three-phase condensing unit nameplate reads 208/230 V, 3 Ph. Supplying it from a single-phase 240 V circuit will:

• ABe acceptable if the breaker is oversized
• BNot produce a rotating field; the three-phase compressor will not run properly and will o…
• CAutomatically convert the motor to single-phase inside the cabinet
• DOnly reduce capacity by about 5 percent

Among common copper water-tube types, which has the thickest wall and is preferred for underground water service?

• AType M
• BType L
• CType K
• DType DWV

A dielectric union or insulating fitting is installed where copper water tube joins steel pipe primarily to:

• AIncrease water velocity
• BStop galvanic corrosion between dissimilar metals
• CServe as the system's expansion tank
• DReplace the shutoff valve

A hydronic heating coil must deliver 40,000 Btu/h with a 20 degF water temperature drop. Using Q = 500 × GPM × ΔT, the required flow is:

• A2 gpm
• B4 gpm
• C8 gpm
• D20 gpm

On a split-system air conditioner, the suction line is insulated primarily to:

• AKeep the compressor warm
• BPrevent condensation on the cold vapor line and limit unwanted heat gain into the returni…
• CRaise head pressure in mild weather
• DReplace the liquid-line filter drier

Pipe hangers and supports are installed to:

• AIncrease friction loss on purpose
• BCarry the weight of pipe, contents, and insulation and control movement without overstres…
• CServe as the electrical grounding electrode
• DReplace isolation valves

IMC 2021 Section 307.2.2 requires the condensate drain inside diameter to be not less than the drain-pan outlet and not less than:

• A3/8 inch
• B1/2 inch
• C3/4 inch
• D2 inch

A closed hydronic heating system that will be raised from 50 degF fill temperature to 180 degF operating temperature requires an expansion tank primarily to:

• AStore extra boiler fuel
• BAccept the increased water volume so pressure stays within the relief-valve setting
• CRemove air only; volume change can be ignored
• DIncrease circulating-pump horsepower

Service isolation valves on hydronic or refrigerant piping should be located so that:

• AThe entire building must be drained to change one coil
• BA single piece of equipment can be isolated, repaired, or replaced without shutting down…
• CValves are concealed above hard ceilings with no access
• DOnly the pump discharge is valved and the suction is left open

A zone has a 36,000 Btu/h sensible cooling load and a 20 degF supply-to-return temperature difference. Using CFM = Qs / (1.08 × ΔT), the required supply airflow is closest to:

• A835 cfm
• B1,110 cfm
• C1,667 cfm
• D2,400 cfm