Nevada C-21B Air Conditioning Contractor Examination

Under UMC 2018 Section 310, a horizontal condensate waste pipe from a cooling coil shall have a slope of not less than:

• A1/8 inch per foot (1 percent) toward the point of disposal
• B1/2 inch per foot toward the air handler
• CLevel, provided the pipe is 1 inch or larger
• D1/4 inch per foot toward the refrigerant suction line

Where overflow from a cooling-coil drain pan would damage the building, UMC 2018 requires which additional protection?

• AA larger primary drain only, with no secondary device
• BA plugged overflow opening so the pan can hold more water
• CA hose from the pan to the roof scupper
• DA secondary drain, an auxiliary pan with its own drain, or a water-level device that shut…

Per UMC 2018 Table 310.3, what is the minimum condensate waste-pipe diameter for a single air-cooling coil of 15 tons, assuming the equipment outlet is not larger?

• A1/2 inch
• B2 inches
• C1-1/4 inches
• D3/4 inch

A Las Vegas packaged rooftop unit is rated 36 tons of refrigeration. Using UMC 2018 Table 310.3 and assuming the factory outlet is not larger, the minimum condensate waste-pipe size is:

• A1 inch
• B3/4 inch
• C1-1/2 inches
• D2 inches

Where cooling-coil condensate is discharged into the building drainage system, UMC 2018 requires the connection to be made:

• AWith a direct sanitary tee into a soil stack
• BBy pumping the water into a potable-water hose bibb
• CBy an indirect waste pipe through an air gap or air break to an approved receptor
• DBy tying the drain into a Type B vent cleanout

New ACR copper refrigerant piping shall be pressure-tested for leaks with which test medium?

• ACompressed oxygen from a cutting-torch cylinder
• BThe system refrigerant, introduced until the gauges reach 400 psig
• CShop compressed air taken from an oiled contractor compressor
• DDry nitrogen or another inert gas, regulated to a safe test pressure

On a split-system air conditioner, the refrigerant suction (vapor) line shall be insulated so that:

• AThe insulation and its vapor retarder stay continuous on the outside of the pipe, limitin…
• BOnly the liquid line is covered, because suction gas is already cold
• CThe insulation is applied under the copper so the pipe can reject heat
• DNo insulation is required on any outdoor line set in Nevada

Which insulation is the usual factory covering for refrigerant suction and chilled-water piping in the C-21B temperature range?

• AClosed-cell elastomeric (flexible foam) pipe insulation
• BUnfaced open-cell fiberglass wrap with no jacket
• CMineral-wool batt stuffed around the tube
• DExpanded polystyrene bead board taped on one side

Duct or pipe insulation installed outdoors and exposed to weather must be protected by:

• AAn extra layer of unfaced fiberglass only
• BA weather jacket or listed outdoor coating that sheds rain and ultraviolet light
• CCloth duct tape wrapped in a spiral
• DNo covering, because Nevada rainfall is low

Factory-made flexible air ducts shall be supported at the manufacturer's intervals, but not farther apart than which spacing, with sag not more than 1/2 inch per foot between supports?

• A2 feet
• BSupports are not required if the duct is stretched tight
• C10 feet
• D4 feet

What is the maximum horizontal support spacing for 1/2-inch steel fuel-gas pipe under NFPA 54 2012 / UMC 2018 Table 1310.3.5.1?

• A6 feet
• B4 feet
• C10 feet
• D15 feet

Per UMC 2018 Table 313.3, what is the maximum horizontal hanger spacing for copper tube 1-1/4 inches and smaller (hydronic or condensate, not fuel gas)?

• A3 feet
• BEvery floor level only
• C12 feet
• D6 feet

Which statement about supporting air-conditioning equipment is correct under UMC 2018?

• AThe refrigerant line set may be used as the sole support for a wall-hung indoor unit
• BThe gas supply pipe may hang a furnace if the load is under 50 pounds
• CEquipment and appliances shall be independently supported; piping and ducts shall not be…
• DFlexible duct may carry the weight of a rooftop unit curb

How should insulated refrigerant or chilled-water piping be supported so the insulation thickness is not lost at the hanger?

• ARest the insulated pipe on a narrow wire so the foam compresses to the copper
• BUse a high-density insert or a saddle wide enough to keep the insulation from crushing
• CLeave a 6-inch uninsulated gap at every hanger
• DHang the pipe from banding wrapped only around the foam jacket

The usual field method to keep a packaged rooftop unit from putting fan vibration into the duct system is to:

• ABolt the supply duct rigid to the unit cabinet with no flexible connector
• BHang the entire rooftop unit from the flex duct
• CFill the duct with acoustic batt so air cannot move
• DInstall a listed flexible duct connector or canvas connection at the unit and, where spec…

In much of Nevada the building code places structures in a high seismic design category. Mechanical equipment such as furnaces, air handlers, and rooftop units shall be:

• ASet on the curb or platform with no fasteners so the unit can slide during an earthquake
• BHeld in place only by the refrigerant line set
• CAnchored and restrained to resist seismic loads, with flexible connectors that allow move…
• DExempt from anchorage because HVAC equipment is not structural

In air-conditioning load work, sensible heat is the portion of the load that:

• AChanges the dry-bulb temperature of the air without changing its moisture content
• BOnly condenses water vapor and never changes dry-bulb temperature
• CIs always exactly one-half of the latent load
• DExists only in evaporative coolers, not in refrigerated coils

A cooling coil delivers 48,000 Btu/h of sensible capacity while moving 2,000 cfm. Using ΔT = Btu/h ÷ (1.08 × CFM), the dry-bulb temperature drop across the coil is closest to:

• A10°F
• B16°F
• C22°F
• D35°F

In the vapor-compression refrigeration cycle used by C-21B air conditioners, heat is rejected to outdoors primarily at which component?

• AThe evaporator coil
• BThe thermostatic expansion valve
• CThe condenser coil
• DThe suction-line accumulator only

Wet-bulb depression is the difference between dry-bulb and wet-bulb temperature. It is most useful on a C-21B job as a measure of:

• AHow much evaporative cooling potential the outdoor air has
• BThe refrigerant saturation temperature at the compressor
• CThe Type B vent clearance to combustibles
• DThe gas-manifold pressure in inches of water column

A rooftop unit moves 1,600 cfm. Entering and leaving air enthalpies differ by 8.0 Btu/lb. Using Qt = 4.5 × CFM × Δh, the total cooling capacity is closest to:

• A12,800 Btu/h
• B28,800 Btu/h
• C57,600 Btu/h
• D96,000 Btu/h

Superheat on a running air conditioner is:

• ASuction-line temperature minus the saturation temperature at the suction pressure
• BLiquid-line temperature minus the outdoor dry-bulb temperature
• CHead pressure divided by suction pressure
• DThe same number as subcooling on every system

An R-410A system shows 119 psig suction pressure and a 52°F suction-line temperature at the evaporator outlet. Saturation temperature at 119 psig is 40°F. The evaporator superheat is:

• A12°F
• B8°F
• C19°F
• D40°F

A split system with a thermostatic expansion valve (TXV) is normally charged in cooling by measuring:

• ACompressor amperage only
• BEvaporator superheat only, as if it had a fixed orifice
• CLiquid-line subcooling, to the manufacturer's target
• DThe outdoor dry-bulb temperature alone

Compared with an R-22 air conditioner of similar capacity, an R-410A unit operates at:

• AAbout the same pressures on both sides
• BOnly low-side pressure; R-410A has no high side
• CA vacuum on the high side whenever it is running
• DSignificantly higher high-side and low-side pressures, and it requires POE oil and 410A-r…

Why must R-22 and R-410A not be mixed in the same circuit?

• AThey have different saturation pressures and oils, so the mixture cannot be charged, reco…
• BR-410A is flammable when mixed with R-22 at any ratio
• CThe building code requires a separate circuit only for aesthetic labeling
• DMixing them lowers head pressure to a safe vacuum

Before a refrigerant circuit is opened for repair, the refrigerant shall be:

• AVented to atmosphere to empty the pipes quickly
• BBurned off at the condensing unit
• CRecovered into an approved cylinder with listed recovery equipment
• DPushed into the occupied space through the supply registers

A liquid-line filter-drier is installed primarily to:

• ARaise the condensing pressure so the TXV can hunt
• BMeter refrigerant in place of a TXV
• CReplace the need for a nitrogen purge while brazing
• DRemove moisture, acid, and particulate before they reach the metering device and compress…

One ton of refrigeration is defined as:

• A12,000 Btu/h
• B1,000 Btu/h
• C24,000 Btu/h
• D90,000 Btu/h

A packaged unit is nameplated 4.0 tons of cooling. Its nominal total cooling capacity is:

• A12,000 Btu/h
• B36,000 Btu/h
• C48,000 Btu/h
• D64,000 Btu/h

Using the common 400 cfm per ton air-conditioning airflow, a 5-ton coil should be supplied with about:

• A800 cfm
• B1,200 cfm
• C2,000 cfm
• D4,000 cfm

A gas furnace delivers 60,000 Btu/h output. The measured temperature rise is 50°F. Using CFM = Btu/h ÷ (1.08 × ΔT), circulating airflow is closest to:

• A400 cfm
• B800 cfm
• C1,110 cfm
• D2,000 cfm

A 10 ft by 8 ft exterior wall has U = 0.10 Btu/h·ft²·°F. Indoor design is 75°F and outdoor design is 108°F. The conduction load through that wall is:

• A264 Btu/h
• B330 Btu/h
• C800 Btu/h
• D8,640 Btu/h

A 50 ft by 40 ft by 10 ft high space has an infiltration rate of 0.50 air changes per hour. Infiltration airflow is CFM = ACH × Volume ÷ 60. The infiltration CFM is closest to:

• A67 cfm
• B1,000 cfm
• C333 cfm
• D167 cfm

A 20,000 ft³ zone has 0.50 ACH of infiltration (167 cfm) and 80 ft² of U-0.10 wall. Indoor 75°F, outdoor 108°F (ΔT = 33°F). Ignoring solar and internals, the combined sensible load of that wall plus infiltration is closest to:

• A264 Btu/h
• B5,950 Btu/h
• C6,210 Btu/h
• D20,000 Btu/h

A small Nevada office has 20 seated occupants (use 250 Btu/h sensible and 200 Btu/h latent each) and 2,000 W of lighting. Using 3.41 Btu/h per watt for the lights, the combined sensible load of people plus lights is closest to:

• A5,000 Btu/h
• B6,820 Btu/h
• C11,820 Btu/h
• D15,820 Btu/h

What lighting heat-gain conversion does Manual N / ASHRAE use for electric lights?

• A1.0 Btu/h per watt
• B3.41 Btu/h per watt
• C12,000 Btu/h per watt
• D341 Btu/h per watt

A Manual N calculation for a Las Vegas retail space shows 54,000 Btu/h sensible and 6,000 Btu/h latent (60,000 Btu/h total). The sensible-heat ratio and the nominal equipment size are:

• ASHR 0.50 and 2.5 tons
• BSHR 0.90 and 5.0 tons
• CSHR 0.10 and 5.0 tons
• DSHR 0.90 and 1.0 ton

The accepted way to measure total supply airflow in a rectangular duct during testing, adjusting, and balancing is to:

• AGuess from the blower nameplate horsepower alone
• BRead only the suction pressure on the refrigerant gauges
• CHold a wet finger in the register until it feels like 400 cfm/ton
• DPerform a Pitot-tube or anemometer traverse and average the velocity readings, then multi…

When proportionately balancing a duct system, the balancer's goal is to:

• AOpen every damper fully and leave the job, regardless of measured cfm
• BClose the return so the supply static pressure is as high as possible
• CBring each outlet to its design cfm (or its design percentage of the fan total) by workin…
• DSet every register to the same grille size and ignore the drawings

On a conventional heat/cool thermostat, the G terminal typically energizes which circuit?

• AThe reversing valve only
• BThe outdoor condensing-unit crankcase heater
• CThe gas valve directly, bypassing all safeties
• DThe indoor blower contractor or fan relay

On most split heat pumps the O thermostat terminal energizes the reversing valve for:

• ACooling (valve energized in cool; de-energized in heat)
• BEmergency heat only, and only above 70°F outdoor
• CThe inducer on a Category I furnace
• DThe condensate float switch

The high-limit control on a gas-fired warm-air furnace is intended to:

• AShut off the burner if supply-air or heat-exchanger temperature exceeds the listed setpoi…
• BHold the room at the thermostat setpoint
• CRegulate manifold gas pressure in inches of water column
• DOpen the evaporative-cooler water valve

A heat pump is selected for 30,000 Btu/h capacity. The building heat loss is 1,200 Btu/h per °F below 70°F indoor. The thermal balance-point outdoor temperature is:

• A25°F
• B45°F
• C55°F
• D70°F

A condensate overflow (float) switch in the drain pan of an air handler should be wired so that a high water level:

• ACloses a circuit that forces the compressor to run continuously
• BOpens the cooling (Y) circuit, and typically the whole 24-volt control, so the coil stops…
• CEnergizes the reversing valve only
• DRaises the gas manifold pressure