Mississippi Residential HVAC Examination

Cooling-season supply duct wrap in an unconditioned Mississippi attic should have its vapor retarder placed on which side of the insulation?

• AOn the outside of the wrap, facing the attic air
• BAgainst the metal, facing the supply air stream
• COmitted entirely if the duct carries only cooled air
• DOn both faces so the insulation is vapor-tight in both directions

Per the energy provisions that IMC Section 604.1 points to, what is the minimum installed R-value for supply and return ducts 3 inches in diameter and larger that run in an unconditioned attic?

• AR-4.2
• BR-6
• CR-8
• DR-12

A crew pulls R-8 flex duct tight through attic trusses so the insulation jacket is compressed to about half its manufactured thickness for most of a 20-foot run. What is the primary thermal result?

• AR-value stays the same because the jacket label still reads R-8
• BInstalled R-value drops because compressed glass fiber has less trapped air
• CR-value increases because the thinner jacket reduces heat-transfer area
• DOnly fire rating is affected; thermal resistance is unchanged

Compared with external duct wrap, internal fibrous duct liner is primarily selected on a residential job when the designer also needs which performance feature?

• AA vapor retarder on the warm side of a cooling duct
• BA higher UL 181 listing than wrap can provide
• CSound absorption in the air stream plus some thermal resistance
• DA substitute for sealing longitudinal seams

IMC Section 603.10 prohibits supporting a metal supply trunk by which method?

• AGalvanized straps fastened to roof trusses
• BHanger wire attached to structural framing
• CAnother duct or the finished ceiling system
• DThreaded rod and a trapeze under a wide trunk

Per SMACNA HVAC Duct Construction Standards (4th edition, 2020), flexible duct hangers should be spaced no farther apart than which interval, and sag between hangers should not exceed which amount?

• A8 feet apart and 1 inch of sag per foot
• B5 feet apart and 1/2 inch of sag per foot
• C10 feet apart and 2 inches of sag per span
• D2 feet apart and no sag allowed

Why do SMACNA and flexible-duct installation standards require a support saddle or strap at least about 1-1/2 inches wide under residential flex?

• ATo electrically bond the inner core to the structure
• BTo keep the hanger from crimping the air path and insulation
• CTo allow the flex to be used as the only equipment vibration isolator
• DTo replace mechanical fasteners at the collar

A 20-inch by 10-inch rectangular supply trunk makes a 90-degree elbow, then a branch takeoff 6 feet later. In addition to the regular SMACNA hanger spacing for that duct size, where should extra supports be provided?

• AOnly at mid-span of the longest straight run
• BWithin about 2 feet of the elbow and within about 4 feet of the branch intersection
• COnly on the downstream side of fire dampers
• DEvery 16 inches to match stud spacing

Which combination best reduces the amount of air-handler vibration that is transmitted into a wood-framed Mississippi residence?

• ARigid sheet-metal connections on supply and return plus the unit bolted hard to the platf…
• BA canvas or flexible duct connector at the unit, plus isolation pads or hangers under the…
• CHigher blower speed so the unit spends less time at each RPM
• DSkipping the filter rack so the blower can run at a lower static pressure

In residential air conditioning, which statement correctly distinguishes sensible heat from latent heat?

• ASensible heat changes air temperature; latent heat is moisture removed or added without t…
• BSensible heat is only solar gain; latent heat is only appliance gain
• CLatent heat is read on a dry-bulb thermometer; sensible heat is read on a wet-bulb thermo…
• DSensible load is always 50 percent of total capacity on every house

A nominal 3-ton residential cooling coil is selected to operate at the common design airflow of 400 cubic feet per minute per ton. What supply airflow should the duct system be designed to deliver?

• A800 cfm
• B1,000 cfm
• C1,200 cfm
• D1,600 cfm

A cooling coil must remove 21,600 Btu/h of sensible heat with a 20 degree F supply-to-return temperature difference. Using Qs = 1.08 × cfm × ΔT, what airflow is required?

• A800 cfm
• B1,000 cfm
• C1,200 cfm
• D1,440 cfm

Which efficiency rating is the seasonal cooling metric used to compare residential air conditioners, as opposed to a single-point or heating-season rating?

• AEER only
• BSEER or SEER2
• CHSPF or HSPF2 only
• DAFUE

On a psychrometric chart, which pair of properties most directly tells a technician whether a coil is removing moisture?

• ADry-bulb temperature and barometric pressure only
• BEntering and leaving wet-bulb or dew-point (humidity) values
• CSupply static pressure and return static pressure
• DCompressor amperage and line voltage

In the vapor-compression cycle used by residential air conditioners, where is heat rejected from the refrigerant to the outdoor air?

• AThe evaporator coil
• BThe metering device
• CThe condenser coil
• DThe suction-line accumulator only

A mixed-air stream of 1,200 cfm is cooled so that its enthalpy drops 6.0 Btu per pound of dry air. Using Qt = 4.5 × cfm × Δh, what total cooling rate is being delivered?

• A8,100 Btu/h
• B21,600 Btu/h
• C32,400 Btu/h
• D43,200 Btu/h

A Manual J cooling load is 30,000 Btu/h total, of which 22,500 Btu/h is sensible. What is the sensible heat ratio (SHR), and what does it imply for coil selection in humid southern Mississippi?

• A0.75 SHR; the coil must still be able to remove the remaining 7,500 Btu/h of latent heat
• B0.25 SHR; almost all of the load is latent
• C1.33 SHR; the equipment should be oversized 33 percent
• D0.75 SHR; latent load can be ignored because it is less than one ton

When a residential R-410A condensing unit is being replaced, what must be done with the existing refrigerant?

• AVent it outdoors after the liquid line is disconnected
• BRecover it into an approved recovery cylinder with listed recovery equipment
• CRecharge it into the new condensing unit without testing
• DBurn it in the furnace heat exchanger to dispose of it

A technician measures 52 degrees F on the suction line at the evaporator outlet. The saturation temperature that corresponds to the suction pressure on the R-410A PT chart is 40 degrees F. What is the evaporator superheat?

• A12 degrees F
• B40 degrees F
• C52 degrees F
• D92 degrees F

Liquid-line pressure on an R-410A system corresponds to a 105 degree F saturation temperature. The liquid line leaving the outdoor coil is 93 degrees F. What is the condenser subcooling?

• A12 degrees F
• B93 degrees F
• C105 degrees F
• D198 degrees F

Which charging method matches the metering device on a typical residential split system?

• ACharge a TXV system by superheat and a fixed-orifice (piston) system by subcooling
• BCharge a TXV system by subcooling and a fixed-orifice (piston) system by superheat
• CCharge both types only by suction pressure
• DCharge both types by adding refrigerant until the compressor amp draw peaks

Compared with a retired R-22 residential system, a matching R-410A system typically requires which combination of service practices?

• AMineral oil, the same service fittings, and charging by sight glass only
• BPOE oil, higher working pressures, and a near-azeotropic PT relationship with very small…
• CHydrocarbon oil, lower discharge pressure, and a large temperature glide like a zeotropic…
• DNo oil change, oxygen as a pressure-test gas, and venting the remaining heel

ACCA Manual J 8th Edition default indoor design conditions for a typical residence are:

• A70 degrees F and 30 percent RH for cooling; 75 degrees F for heating
• B75 degrees F and 50 percent RH for cooling; 70 degrees F for heating
• C78 degrees F and 60 percent RH for cooling; 68 degrees F for heating
• D72 degrees F and 40 percent RH year-round

For a 3-bedroom house, how many occupants should a standard Manual J cooling load include, and what default internal gains are assigned to each occupant?

• A3 occupants at 400 Btu/h sensible only
• B4 occupants at 230 Btu/h sensible and 200 Btu/h latent each
• C6 occupants at 1,000 Btu/h total each
• D1 occupant at 230 Btu/h sensible and 200 Btu/h latent

A net exterior wall area of 280 square feet has U = 0.08 Btu/h·ft²·°F. Indoor cooling design is 75 degrees F and outdoor cooling design is 95 degrees F. What is the wall's conductive cooling load?

• A448 Btu/h
• B1,680 Btu/h
• C2,240 Btu/h
• D3,360 Btu/h

On a single-zone central system, Manual J uses which load to select the equipment, and which loads to size the room air outlets?

• AThe block (whole-house) load for equipment; room-by-room loads for air distribution
• BThe largest bedroom load for equipment; the block load for outlets
• CThe sum of all peak room loads for equipment, ignoring diversity
• DA 500-square-foot-per-ton rule for both equipment and outlets

A salesperson tells a Jackson homeowner to 'just put in 1 ton per 500 square feet and then add half a ton for safety.' What is the correct Manual J / Manual S response?

• AAgree, because Manual J requires a 15 percent safety factor on every job
• BReject the rule of thumb; calculate the load, then select the next appropriate equipment…
• CUse the rule of thumb for cooling but Manual J only for heating
• DDouble the rule-of-thumb tonnage because Jackson is humid

Why does Manual J add a duct-gain/duct-loss component when a supply-and-return system is placed in a vented, unconditioned Mississippi attic?

• ABecause attic ducts are always assumed to leak 50 percent of the airflow
• BBecause the attic air is hotter (and in winter colder) than the conditioned air, so condu…
• CBecause Manual J forbids attic ducts, so the load is a penalty that forces relocation
• DBecause the energy code R-value already includes duct load, so Manual J would double-coun…

A one-story house has the following cooling sensible pieces: walls 1,800 Btu/h, glass 6,400 Btu/h, ceiling 2,200 Btu/h, infiltration 1,600 Btu/h, occupants and appliances 2,400 Btu/h, and attic duct gain 1,500 Btu/h. What is the block sensible cooling load?

• A12,400 Btu/h
• B14,400 Btu/h
• C15,900 Btu/h
• D18,400 Btu/h

A bedroom has a peak sensible cooling load of 3,240 Btu/h. The supply air is 20 degrees F colder than room air. Using cfm = Qs / (1.08 × ΔT), how much supply air should that room receive?

• A100 cfm
• B150 cfm
• C200 cfm
• D300 cfm

Total external static pressure (TESP) on a residential air handler is measured how, and what is it used for during testing, adjusting, and balancing?

• AA single probe in the supply plenum; it is used only to set gas manifold pressure
• BThe sum of the absolute supply-plenum and return-plenum static readings, compared with th…
• CVelocity pressure at one supply register multiplied by the number of rooms
• DThe difference between outdoor barometric pressure and indoor dry-bulb

Most residential gas-furnace and split-system thermostats switch which control voltage to the gas valve, compressor contactor, and reversing valve?

• A24 volts AC from a control transformer
• B120 volts AC from the branch circuit
• C12 volts DC from a battery pack
• D480 volts AC from a step-up transformer

On a conventional heat-pump thermostat, the O/B terminal is used to control which component?

• AThe indoor blower only
• BThe reversing valve
• CThe crankcase heater
• DThe condensate float switch

A high-limit switch on a gas furnace is primarily intended to:

• ALight the burners if the igniter fails
• BShut off the gas valve if heat-exchanger temperature rises above a safe setpoint, usually…
• CEnergize the reversing valve in defrost
• DProve that the condensate pump is running

On an induced-draft 80 percent furnace, the pressure switch typically proves which condition before the ignition control will open the main gas valve?

• AThat the circulating blower has reached high speed
• BThat the draft inducer is running and the vent is establishing the intended negative pres…
• CThat manifold pressure is exactly 10 inches water column
• DThat the outdoor temperature is below the heat-pump balance point

A mechanical-heat thermostat has an adjustable heat anticipator. If the anticipator is set to a much lower current than the actual heating-control circuit current, what is the most likely operating symptom?

• ALonger-than-design on-cycles and room temperature overshoot
• BShorter-than-design on-cycles and the room may not reach setpoint
• CThe reversing valve will stick in cooling
• DThe draft inducer will not start

What is the function of the reversing valve on a residential air-source heat pump?

• AIt reverses indoor blower rotation for defrost
• BIt routes discharge gas to the indoor coil for heating and to the outdoor coil for cooling
• CIt bypasses the metering device so the system can run on refrigerant pressure alone
• DIt isolates the compressor crankcase heater during cooling

Why does an air-source heat pump initiate a defrost cycle?

• ATo cool the compressor windings on a hot day
• BTo melt frost or ice that has accumulated on the outdoor coil during heating operation
• CTo equalize refrigerant charge between the indoor and outdoor coils after a power failure
• DTo purge noncondensables from the accumulator

The thermal balance point of a heat-pump-plus-auxiliary-heat system is the outdoor temperature at which:

• AThe heat pump's heating capacity equals the building heating load
• BThe reversing valve must be energized continuously
• CDefrost is no longer required
• DSEER2 equals HSPF2

When setting a residential condensing unit or heat-pump outdoor section, which clearance practice is consistent with typical manufacturer instructions and IMC equipment-access rules?

• APush the unit tight to the wall on all sides to shade it
• BProvide the manufacturer's required service and air-inlet clearances, keep the coil off g…
• CInstall the unit in a sealed crawl space so it cannot freeze
• DSet the unit under the dryer exhaust so the coil stays wet and clean

On a heat-pump thermostat, what is the difference between auxiliary heat and emergency heat?

• AAuxiliary heat stages on automatically to help the heat pump; emergency heat locks out th…
• BThey are identical; both run the compressor at high speed
• CEmergency heat is only the reversing valve; auxiliary heat is only the blower
• DAuxiliary heat is used in cooling; emergency heat is used in defrost only

When possible, a residential split-system heat pump should be charged in which operating mode, and why?

• AHeating mode, because the outdoor coil is smaller
• BCooling mode, because that is the condition for which the factory charge, superheat, and…
• CDefrost mode, because both coils are active
• DOff, by weighing in the nameplate charge plus the entire cylinder

A fixed-orifice air conditioner on a 95 degree F day shows very low superheat, high suction pressure, and a cool compressor. Indoor airflow has not been measured yet. Which diagnosis is most consistent?

• AA starved evaporator from an undercharge
• BAn overcharge, a dirty indoor filter/low airflow, or both
• CA blocked outdoor coil only
• DA failed compressor start capacitor only

A heat pump is selected from an extended-capacity table. At 47 degrees F outdoor it delivers 36,000 Btu/h; at 17 degrees F it delivers 21,000 Btu/h. The Manual J heating load at the 25 degree F outdoor design is 28,000 Btu/h. What does this imply?

• AThe unit can carry the entire design heating load at 25 degrees F without auxiliary heat
• BCapacity at 25 degrees F will fall between 21,000 and 36,000 Btu/h and will be less than…
• CThe unit is a 3-ton cooler and therefore automatically a 3-ton heater at every outdoor te…
• DManual J heating load should be discarded and the 47 degree F rating used for sizing

AFUE on a residential furnace nameplate is best described as:

• AThe seasonal fraction of fuel input that becomes useful heat, including jacket and cyclin…
• BThe exact temperature rise across the heat exchanger
• CThe gas manifold pressure in inches of water column
• DThe maximum vent connector length in feet