Nevada C-21A Refrigeration Contractor Examination

NAC 624.380 limits Nevada C-21A refrigeration work to devices and machinery that control air temperatures in which range?

• ABelow 50°F in refrigerators, refrigerated rooms, and insulated spaces
• B55°F to 75°F comfort cooling in occupied offices
• CAny temperature, including warm-air heating
• DOnly ice-rink floors below 32°F

In the vapor-compression cycle used on a walk-in freezer, which four components appear in order of refrigerant flow?

• ACompressor, condenser, metering device, evaporator
• BEvaporator, condenser, compressor, metering device
• CCondenser, evaporator, metering device, compressor
• DMetering device, compressor, evaporator, condenser

What is the evaporator's job in a 0°F walk-in freezer?

• AAbsorb heat from the box air so the refrigerant vaporizes
• BReject heat to outdoor air and condense the refrigerant
• CRaise refrigerant pressure without changing enthalpy
• DStore unused liquid refrigerant for winter head pressure

Where does a refrigeration system reject the heat it removed from a refrigerated room?

• AAt the condenser (or condensing unit) to air or water
• BAt the TXV bulb
• CAt the crankcase heater
• DOnly through the suction-line insulation

How is evaporator superheat calculated on a DX freezer coil?

• AActual suction-vapor temperature minus saturation temperature at the suction pressure
• BBox temperature minus condenser saturation temperature
• CLiquid-line temperature minus outdoor dry-bulb
• DDischarge temperature minus suction temperature

How is liquid-line subcooling calculated on an air-cooled condensing unit?

• ASaturation temperature at liquid-line (or discharge) pressure minus actual liquid-line te…
• BOutdoor wet-bulb minus liquid-line temperature
• CSuction saturation minus box temperature
• DDischarge temperature minus condensing temperature only

One ton of refrigeration is defined as which heat rate?

• A12,000 Btu/h (200 Btu/min)
• B1,000 Btu/h
• C3,412 Btu/h
• D288,000 Btu/h

Under ASHRAE 34 as used in UMC 2018 Table 1102.3, R-404A is classified in which safety group?

• AA1 (lower toxicity, no flame propagation)
• BB2L (higher toxicity, lower flammability)
• CA3 (lower toxicity, higher flammability)
• DB3 (higher toxicity, higher flammability)

UMC 2018 classifies a refrigeration system as high-probability when which condition is true?

• AA leak from a failed connection, seal, or component could enter an occupied space
• BThe compressor nameplate exceeds 5 horsepower
• CThe refrigerant is any Group A1 fluid
• DThe condenser is located outdoors

In the ASHRAE 34 / UMC 2018 refrigerant safety-group letter, what does Group B indicate?

• AHigher toxicity than Group A
• BNo flame propagation
• CLower flammability than Group A
• DThe refrigerant is always ammonia

A −10°F walk-in freezer using R-404A shows 16 psig at the evaporator and a well-insulated outlet temperature of 0°F. What is the evaporator superheat?

• A20°F
• B10°F
• C16°F
• D0°F

An air-cooled R-404A condensing unit serving a walk-in cooler reads 272 psig on the liquid line. The liquid-line temperature leaving the condenser is 95°F. What is the subcooling?

• A15°F
• B5°F
• C27°F
• D95°F

A 0°F walk-in freezer is designed for a 10°F evaporator TD. What saturated suction temperature should the coil run at with a clean, fully loaded coil?

• A−10°F
• B0°F
• C10°F
• D−20°F

A 35°F meat cooler TXV is running 25°F superheat and the sight glass is flashing. What is the most likely first cause?

• AA starved evaporator from undercharge or a liquid-line restriction
• BAn overcharged system flooding the compressor
• CA TXV stuck fully open
• DA condenser fan that will not run

A freezer compressor returns with slugging damage. Running data showed 2°F superheat at the evaporator outlet and frost back to the compressor. What does that indicate?

• AFloodback — liquid leaving the evaporator
• BA severely starved TXV
• CNormal low-temperature operation
• DOnly a dirty condenser

UMC 2018 Table 1102.3 lists anhydrous ammonia (R-717) in which safety group?

• AB2L
• BA1
• CA2L
• DB1

Why are transcritical or cascade designs used for R-744 (CO2) low-temperature racks instead of a simple air-cooled condenser on a hot Nevada afternoon?

• ACO2's critical temperature is about 87.8°F, so it will not condense above that temperature
• BCO2 cannot be used below 50°F
• CCO2 is Group A3 and is banned indoors
• DCO2 has no pressure-temperature relationship

UMC 2018 Table 1102.3 refrigerant concentration limit (RCL) is used primarily to determine which of the following?

• AThe maximum pounds of refrigerant permitted in a high-probability system for a given occu…
• BThe factory oil charge in fluid ounces
• CThe minimum suction-line velocity in fpm
• DThe cooling-tower approach in degrees Fahrenheit

A single independent R-404A circuit serving a high-probability occupied space exceeds the Table 1102.3 quantity for that volume. What does UMC 2018 require?

• AA refrigeration machinery room (or another listed compliance path such as outdoor equipme…
• BOnly a larger TXV
• CReplacement of R-404A with R-290 without other changes
• DNothing; A1 refrigerants have no quantity limit

UMC 2018 Equation 1106.2.5.1 sets emergency machinery-room exhaust at Q = 100√G cfm, where G is the refrigerant mass in the largest system in pounds. What airflow is required for a 225 lb R-404A rack?

• A1,500 cfm
• B225 cfm
• C22,500 cfm
• D100 cfm

UMC 2018 1106.2.2.1 requires the machinery-room refrigerant detector to actuate the alarm and mechanical ventilation at a setpoint not more than which value?

• AThe refrigerant's Occupational Exposure Limit (OEL) from Table 1102.3
• B50 percent of the refrigerant's critical pressure
• CThe high-pressure-control cut-out
• D1 percent by volume for every refrigerant

Why must a new R-404A / POE walk-in system be evacuated to a deep vacuum and kept dry before charging?

• APOE oil is strongly hygroscopic and moisture plus oil forms acids and sludge
• BPOE oil will not mix with R-404A unless water is present
• CA wet system raises evaporator TD to a safer value
• DMoisture is required to make the sight glass show green

R-448A used as a low-temperature R-404A retrofit has noticeable temperature glide. How should saturation temperature be read for superheat?

• AUse dew-point temperature at the suction pressure
• BUse bubble-point temperature at the suction pressure
• CAverage the outdoor dry-bulb and wet-bulb
• DIgnore the P/T chart and use box temperature as saturation

Most of the cooling in a DX walk-in coil comes from which process?

• ALatent heat of vaporization as liquid refrigerant boils in the evaporator
• BSensible cooling of already-superheated discharge vapor
• CFriction in the suction line
• DHeat added by the crankcase heater

Why do low-temperature reciprocating compressors need some suction superheat and often a de-superheating or cooling scheme?

• ATo keep liquid out of the cylinders and to carry compressor heat out in the discharge vap…
• BTo raise evaporator TD to 25°F
• CTo eliminate the need for a high-pressure control
• DTo allow oxygen to be used for leak testing

A supermarket uses R-404A only in a rooftop chiller that cools propylene glycol circulated through walk-in coils. How does UMC 2018 classify that refrigeration system?

• ALow-probability, because a refrigerant leak is isolated from the occupied sales floor
• BHigh-probability, because glycol can leak
• CGroup A3 regardless of piping
• DNot a refrigeration system under Chapter 11

R-290 (propane) is sometimes used in small self-contained freezers. What is its ASHRAE 34 / UMC 2018 safety group, and what is the practical result?

• AA3 — higher flammability; charge and occupancy limits are very small
• BA1 — treated exactly like R-404A
• CB1 — toxic but nonflammable
• DA2L — same rules as R-32 rooftop comfort units

A 35°F produce cooler is designed for an 8°F evaporator TD. The coil SST is 17°F (R-404A ≈ 53 psig) and a clean-coil outlet reads 32°F. Which statement is correct?

• ATD is 18°F and superheat is 15°F — the coil is undersized or restricted and starved
• BTD is 8°F and superheat is 8°F — the coil is on design
• CTD is 15°F and superheat is 18°F — only the TXV is overfeeding
• DTD is 0°F because the outlet is below box temperature

A machinery room contains a 90 lb walk-in system and a 400 lb rack, both R-404A (A1). What emergency exhaust does Equation 1106.2.5.1 require?

• A2,000 cfm, based on the 400 lb system only
• B4,900 cfm, based on 90 + 400 = 490 lb
• C900 cfm, based on the 90 lb system
• D400 cfm, equal to the larger charge

After a nitrogen pressure test, a new POE / R-404A freezer is evacuated. Which standing vacuum is the usual Modern Refrigeration / industry deep-vacuum target before charging?

• A500 microns (0.5 mm Hg absolute) with a decay check
• B30 inches Hg on a compound manifold gauge only
• C20 psig vacuum
• D14.7 psia

A P-h diagram gives liquid enthalpy entering the freezer TXV as 45 Btu/lb and evaporator-outlet vapor enthalpy as 85 Btu/lb. What is the net refrigeration effect, and what does the missing 45 Btu/lb represent if saturated liquid at condenser pressure was 50 Btu/lb and vapor at evaporator pressure is 90 Btu/lb latent?

• A40 Btu/lb NRE; the drop from full latent effect is flash gas through the TXV
• B85 Btu/lb NRE; flash gas adds capacity
• C45 Btu/lb NRE; the compressor produces that cooling
• D130 Btu/lb NRE; add the two enthalpies

R-404A suction at a −20°F freezer evaporator is 16 psig. At the compressor, after 80 ft of suction line, the pressure is 13 psig, which the P/T chart lists as −25°F. What is the equivalent suction-line temperature drop, and is it acceptable versus a 2°F design?

• A5°F — high; the line is undersized or too long
• B3 psig — report drop in psi only; temperature drop is not used
• C45°F — subtract −25 from +20
• D0°F — pressure drop does not change saturation temperature

A 20 ft × 20 ft × 10 ft 0°F freezer has 1,600 ft² of envelope and 4-inch urethane with U = 0.030 Btu/h·ft²·°F. Outdoor design is 90°F. What is the transmission load only?

• A4,320 Btu/h
• B1,600 Btu/h
• C48,000 Btu/h
• D288,000 Btu/h

A −40°F process freezer uses a CO2 low stage cascaded onto an R-404A high stage. What is the purpose of the cascade condenser/evaporator?

• AThe R-404A system condenses the CO2 so the low stage never has to reject heat to air abov…
• BIt lets both refrigerants mix in a single DX coil
• CIt replaces the TXV on the low stage
• DIt converts the plant to comfort cooling above 50°F

Copper linesets for a field-erected walk-in refrigeration system shall comply with which standard under UMC 2018 1109.1.2?

• AASTM B280 or ASTM B1003
• BASTM B88 Type M only
• CASTM A53 Type F steel
• DASTM D1785 Schedule 40 PVC

UMC 2018 1109.1 requires refrigerant piping to be which of the following?

• AMetallic
• BAny listed plastic rated for 150 psig
• CPEX-A with oxygen barrier
• DCPVC on the suction side only

UMC 2018 1109.6 requires refrigerant piping and tubing to be supported at intervals not exceeding which distance?

• A15 feet
• B4 feet
• C25 feet
• D50 feet

UMC 2018 1109.8 requires refrigerant piping and joints erected on the premises to be which of the following before they are covered?

• AExposed to view for visual inspection
• BPainted with aluminum paint only
• CWrapped in duct tape as a vapor retarder
• DCharged with the full operating refrigerant charge

While brazing ACR copper on a freezer suction line, what should flow through the tube?

• ADry nitrogen at a low flow to displace oxygen
• BOxygen to keep the interior bright
• CCompressed air from an oil-lubricated shop compressor
• DThe final R-404A charge

UMC 2018 1109.7 limits soft annealed copper tubing used for refrigerant to a maximum nominal size of which value?

• A1-3/8 inches
• B2-1/8 inches
• C3/8 inch
• D4 inches

Under UMC 2018 1109.7, mechanical joints other than approved press-connect joints shall not be made on tubing larger than which size?

• A3/4 inch nominal
• B1-3/8 inch nominal
• C2 inch IPS
• D1/4 inch OD

After the first bend in refrigeration tubing leaving the compressor, UMC 2018 1109.6 requires a permanent support within how many feet?

• A6 feet
• B2 feet
• C15 feet
• D20 feet

UMC 2018 1109.4 requires refrigerant piping that crosses an open passageway to be not less than how high above the floor, unless it is against the ceiling and the AHJ permits it?

• A7.25 feet (7 feet 3 inches)
• B6 feet 8 inches
• C5 feet
• D4 feet

UMC 2018 1109.5 requires underground refrigerant piping to be protected against which condition?

• ACorrosion
• BUltraviolet chalking only
• CFreezing of the refrigerant into a solid
• DLoss of superheat

UMC 2018 1109.1.3 requires iron or steel refrigerant pipe larger than 2 inches iron pipe size to be which type?

• AElectric-resistance welded or seamless
• BFurnace-butt-welded Type F
• CCast-iron soil pipe
• DGalvanized EMT

A −20°F suction line runs through a 75°F machinery room. Where must the vapor retarder be placed on the insulation?

• AOn the outside (warm face), sealed at every joint and hanger
• BAgainst the copper under the insulation
• COnly at the compressor end
• DVapor retarders are omitted below 50°F