Arizona ROC C-39/CR-39/R-39R Air Conditioning and Refrigeration Examination

An HVAC technician is troubleshooting an R-410A commercial split system. The liquid line gauge pressure reads 318 psig (corresponding to a saturated condensing temperature of 100°F), and the measured liquid line temperature at the outlet of the condenser coil is 88°F. What is the system subcooling, and what does this indicate if the manufacturer design subcooling is 12°F?

• ASubcooling is 6°F; the system is undercharged or has a metering valve over-feeding.
• BSubcooling is 12°F; the system subcooling matches manufacturer specification exactly.
• CSubcooling is 18°F; the system has a non-condensable gas or severe restriction.
• DSubcooling is 24°F; the condenser coil is severely fouled or overcharged.

A walk-in cooler operating on R-404A has a suction pressure of 58 psig (saturated evaporator temperature of 25°F). The measured suction line temperature 6 inches downstream of the evaporator bulb attachment point is 41°F. What is the operating evaporator superheat?

• A8°F
• B16°F
• C24°F
• D33°F

Under EPA Section 608 regulations, what level of evacuation must be achieved when disposing of or majorly servicing a high-pressure commercial appliance containing 250 lbs of R-410A using recovery equipment manufactured on or after November 15, 1993?

• A0 psig (atmospheric pressure)
• B4 inches of Hg vacuum
• C15 inches of Hg vacuum
• D10 inches of Hg vacuum

When mounting a Thermostatic Expansion Valve (TEV) sensing bulb on a horizontal suction line with an outside diameter of 1-1/8 inches, what is the proper clock position for the bulb attachment?

• AAt the 4 o'clock or 8 o'clock position
• BDirectly on top of the pipe at the 12 o'clock position
• CDirectly at the bottom of the pipe at the 6 o'clock position
• DOutside the insulated sleeve exposed to ambient air

What is the primary function of a compressor crankcase heater in a commercial air conditioning or refrigeration system?

• ATo increase discharge gas superheat during normal compressor operation
• BTo heat the suction gas prior to entering the compressor cylinders to boost volumetric ef…
• CTo prevent liquid refrigerant migration to compressor crankcase oil during the off-cycle
• DTo melt ice accumulation on the compressor shell during low-ambient cooling

R-407C is a zeotropic blend (R-32/R-125/R-134a). When calculating superheat for a system operating with R-407C, which pressure-temperature curve value must be used?

• ABubble point temperature from the P-T chart
• BMean average temperature between bubble point and dew point
• CDew point temperature from the P-T chart
• DCritical point temperature of R-134a

Per EPA Section 608 regulations, what is the maximum allowable annual leak rate threshold for commercial refrigeration equipment containing 50 lbs or more of refrigerant before mandatory repair is required within 30 days?

• A20%
• B10%
• C30%
• D50%

A commercial low-temperature walk-in freezer evaporator coil utilizes a 4,800 Watt electric defrost heater powered by a 208 Volt single-phase supply. What current draw should a technician read with a clamp-on ammeter when testing the defrost circuit?

• A11.5 Amps
• B17.3 Amps
• C23.1 Amps
• D38.4 Amps

Where must an oil separator be installed in a commercial refrigeration system, and how does it return oil back to the compressor?

• AIn the discharge line as close to the compressor as possible; oil is returned to the cran…
• BIn the suction line before the accumulator; oil flows via gravity to the oil sump.
• CIn the liquid line after the receiver; oil is pumped using a high-pressure auxiliary oil…
• DIn the hot gas bypass line; oil returns during the defrost cycle only.

In an automatic pump-down refrigeration system, what component initiates the compressor shutoff sequence when room temperature is satisfied?

• AThe high-pressure safety cutout switch
• BThe evaporator defrost timer breaking power directly to the compressor contactor coil
• CThe thermal overload protector inside the compressor motor windings
• DThe room thermostat closing the liquid line solenoid valve, causing low-side pressure to…

According to ASHRAE Standard 15 and the International Mechanical Code (IMC), what action must automatically occur when a machinery room refrigerant vapor detector senses refrigerant concentration exceeding the Occupational Exposure Limit (OEL) or Threshold Limit Value (TLV)?

• AClose all chilled water isolation valves and energize the boiler feed pumps
• BShut down the building fire alarm system to prevent false evacuation calls
• CStart emergency mechanical exhaust ventilation and sound an audible/visual alarm inside a…
• DOpen all roof relief dampers and inject nitrogen into the refrigerant piping

What internal feature inside a suction line accumulator allows compressor oil to return to the crankcase while preventing liquid refrigerant from slugging the compressor?

• AA U-tube with an oil bleed hole (metering orifice) at the bottom of the loop
• BA thermostatic expansion element in the top shell
• CA high-pressure bypass check valve set at 150 psig
• DA desiccant core that chemically absorbs liquid refrigerant

An R-410A air-cooled commercial condensing unit has a Design Working Pressure (DWP) of 450 psig on the high side. Per IMC and ASHRAE 15 recommendations, what is the maximum allowable setting for the manual reset high-pressure safety cutout control?

• A300 psig
• B405 psig
• C450 psig
• D550 psig

How does a hot gas bypass valve maintain evaporator suction pressure during low-load operating conditions in a commercial air conditioning system?

• ABy routing high-pressure liquid refrigerant directly into the liquid line receiver
• BBy closing the suction line shutoff valve to throttle refrigerant flow
• CBy modulating discharge gas from the compressor outlet directly into the suction line or…
• DBy energizing the condenser fan speed controller to increase head pressure

During a system inspection, a technician notes a high head pressure, high subcooling (22°F), high superheat (35°F), and low suction pressure on a system equipped with a thermostatic expansion valve. What is the most probable fault?

• ARefrigerant system overcharge
• BEvaporator fan motor running backward
• CLiquid line filter-drier restriction or clogged TEV inlet screen
• DNon-condensable air trapped in the condenser coil

An office building air handling unit has a measured sensible cooling load of 36,000 BTU/h and a latent cooling load of 12,000 BTU/h. What is the Sensible Heat Ratio (SHR) for this cooling application?

• A0.25
• B0.75
• C0.33
• D0.67

A 5-ton split system air conditioner (sensible cooling capacity of 43,200 BTU/h at standard ARI rating) operates with a supply air temperature of 55°F and a return air temperature of 75°F (ΔT = 20°F). What supply airflow rate in CFM is required across the evaporator coil?

• A1,200 CFM
• B2,000 CFM
• C1,600 CFM
• D2,400 CFM

When sizing supply trunk ductwork using the Equal Friction design method per ACCA Manual D / SMACNA standards, what is the standard recommended design friction rate per 100 feet of equivalent duct length for residential and light commercial systems?

• A0.01 to 0.02 in. w.c.
• B0.25 to 0.50 in. w.c.
• C1.00 to 1.50 in. w.c.
• D0.08 to 0.10 in. w.c.

In a 3-pipe Variable Refrigerant Flow (VRF) heat recovery system, how does the system enable simultaneous heating in zone A and cooling in zone B?

• ABy reversing the outdoor compressor rotation direction every 15 minutes
• BBy utilizing electric auxiliary duct heaters in all cooling zones
• CBy operating two separate outdoor condensing units connected to a shared water loop
• DBy using a Branch Selector (BS) box to route high-pressure discharge gas to zone A and li…

An air handler processes 3,000 CFM of air. The entering air enthalpy is 34.0 BTU/lb of dry air, and the leaving air enthalpy is 26.0 BTU/lb. What is the total cooling capacity of the air handler in BTU/h and tons of refrigeration?

• A25,920 BTU/h (2.16 Tons)
• B72,000 BTU/h (6.0 Tons)
• C108,000 BTU/h (9.0 Tons)
• D129,600 BTU/h (10.8 Tons)

Per IMC Section 307.2, condensate drain lines from air conditioning coils must be sized based on equipment cooling capacity. What is the minimum required nominal pipe size for a 6-ton commercial air handler condensate drain line?

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

A technician measures a return plenum static pressure of -0.28 in. w.c. and a supply plenum static pressure of +0.32 in. w.c. downstream of the cooling coil on a packaged air conditioner. What is the Total External Static Pressure (TESP) operating on the blower?

• A0.60 in. w.c.
• B0.04 in. w.c.
• C0.28 in. w.c.
• D0.32 in. w.c.

During the defrost cycle of an air-source heat pump, what actions are simultaneously taken by the defrost control board to clear ice from the outdoor coil?

• AEnergize reversing valve to heating mode, run outdoor fan at double speed, and shut off c…
• BEnergize reversing valve to cooling mode, shut off outdoor fan motor, and energize auxili…
• CDe-energize reversing valve, open outdoor bypass dampers, and shut off indoor blower motor
• DDe-energize compressor, run indoor blower in reverse, and open hot gas expansion valve

How does reducing supply fan airflow from 400 CFM per ton down to 320 CFM per ton affect air conditioning system performance?

• AIncreases evaporator coil temperature and increases sensible heat removal
• BIncreases total system cooling capacity in Tons by 25%
• CPrevents condensate formation on the cooling coil completely
• DLowers evaporator coil temperature, increases latent dehumidification, and lowers Sensibl…

An air-side economizer installed on a rooftop unit utilizes fixed dry-bulb temperature changeover. Per ASHRAE Standard 90.1 / IECC for dry climate zones (such as Phoenix, Arizona), what is the typical maximum outdoor air high-limit shutoff temperature setting?

• A55°F
• B65°F
• C85°F
• D75°F

What is the primary operational advantage of a two-stage scroll compressor compared to a single-stage compressor in residential split-system air conditioning?

• AEliminates the need for a run capacitor on the outdoor fan motor
• BOperates at approximately 65-70% capacity on first stage for enhanced humidity control an…
• CAllows the system to run on 120 Volt single-phase power during peak demand periods
• DReverses refrigerant flow without utilizing a 4-way reversing valve

According to ACCA Manual T standards for air distribution outlet selection, what supply air face velocity range is recommended for residential ceiling diffusers to avoid occupant drafts and air noise?

• A100 to 250 FPM
• B1,200 to 1,500 FPM
• C2,000 to 2,500 FPM
• D400 to 600 FPM

Per IMC Section 603.6 and SMACNA installation standards, flexible air ducts must be supported at maximum intervals of how many feet, and what is the maximum allowed sag between supports?

• A6 feet max support spacing; 1/2 inch max sag per foot
• B4 feet max support spacing; 1/2 inch max sag per foot
• C8 feet max support spacing; 2 inches max sag per foot
• D10 feet max support spacing; 1 inch max sag per foot

What is the key functional difference between a 2-way modulating chilled water coil control valve and a 3-way modulating control valve?

• AA 2-way valve maintains constant water flow through the system piping loop while a 3-way…
• BA 2-way valve is controlled by line voltage; a 3-way valve operates only on pneumatic 3-1…
• CA 2-way valve is installed on the supply pipe; a 3-way valve must be installed on the con…
• DA 2-way valve varies total hydronic loop flow; a 3-way valve bypasses excess water around…

A rooftop unit economizer is supplying 20% outdoor air at 90°F dry-bulb and 80% return air at 75°F dry-bulb. What is the calculated mixed air dry-bulb temperature entering the cooling coil?

• A75.0°F
• B78.0°F
• C82.5°F
• D87.0°F

A gas-fired warm air furnace has a rated bonnet heat output of 80,000 BTU/h. The measured supply airflow is 1,400 CFM. What is the calculated air temperature rise across the furnace heat exchanger?

• A52.9°F
• B38.5°F
• C68.0°F
• D74.1°F

Per NFPA 54 / International Fuel Gas Code (IFGC), when taking combustion air from indoor spaces using two permanent openings to an adjacent room on the same story, what is the minimum required net free area for each opening per 1,000 BTU/h of total input rating?

• A2 square inches per 1,000 BTU/h
• B1 square inch per 1,000 BTU/h (minimum 100 sq. in.)
• C4 square inches per 1,000 BTU/h
• D1 square inch per 4,000 BTU/h

What is the minimum required clearance to combustible construction for a listed Type B double-wall gas vent pipe passing vertically through a residential floor or ceiling joist assembly?

• A1/4 inch
• B2 inches
• C1 inch
• D6 inches

What is the required safety procedure when an HVAC inspection reveals a crack penetrating through the metal wall of a gas furnace clam-shell heat exchanger?

• ASeal the crack using high-temperature silicone sealant and resume operation
• BReduce gas manifold pressure from 3.5 in. w.c. to 2.0 in. w.c. to lower flame height
• CShut off the gas supply, lock out/tag out the unit, notify the owner, and replace the hea…
• DIncrease supply blower speed to maximum to dilute flue gases entering the supply duct

Per IFGC and IMC requirements, Category IV high-efficiency condensing gas furnaces generate acidic flue condensate. What pitch or slope must be maintained on horizontal PVC/CPVC vent pipe runs?

• ALevel (0 pitch per foot)
• BMinimum 1/8 inch per foot sloped downward away from furnace
• CMinimum 1/4 inch per foot sloped upward back toward the furnace
• DMinimum 1 inch per foot sloped downward to an outdoor splash block

A furnace primary high-limit switch trips repeatedly during heating operation. Diagnostic testing shows the gas manifold pressure is normal. What is the most likely mechanical cause of the high-limit trip?

• AFailed flame sensor rod
• BRestricted return air filter or severely fouled evaporator coil reducing supply airflow
• CShort-circuited 24V thermostat wire
• DOpen auxiliary rollout switch

An electric air handler unit contains a 15 kW supplemental resistance electric strip heater rated at 240 Volts. What is the heat output capacity in BTU per hour?

• A15,000 BTU/h
• B34,120 BTU/h
• C68,240 BTU/h
• D51,180 BTU/h

When testing a flame rectification system on a modern direct spark ignition (DSI) or hot surface ignition (HSI) furnace, what electrical signal must be measured through the flame rod wire while the burner is firing?

• A24 to 120 Volts AC
• B10 to 50 Milliamps (mA) AC
• C1.0 to 5.0 Microamps (µA) DC
• D500 to 750 Millivolts (mV) DC

What is the official designation for a gas ignition control module that attempts ignition for a specific trial period (e.g. 4 seconds) and, if flame is not established, retries 3 times before locking out ignition?

• ASingle-try non-lockout control
• BContinuous pilot re-ignition system
• CStanding pilot thermocouple safety shutoff
• D100% Shutoff Lockout with Intermittent Retry

What is the standard recommended manifold gas pressure for a residential warm air furnace equipped with a single-stage Natural Gas valve?

• A3.5 in. w.c.
• B1.5 in. w.c.
• C7.0 in. w.c.
• D11.0 in. w.c.

In heat pump terminology, what defines the 'Thermal Balance Point' of a residential heat pump system?

• AThe outdoor temperature where indoor relative humidity reaches 50%
• BThe outdoor temperature where the heating output of the heat pump exactly matches the bui…
• CThe indoor temperature where auxiliary electric heat switches off completely
• DThe suction temperature where reversing valve solenoid coils energize

Per IFGC Section 304.6.1, when bringing combustion air directly from the outdoors using two vertical air ducts, what is the required net free area of each duct per 1,000 BTU/h of total input rating?

• A1 square inch per 4,000 BTU/h
• B1 square inch per 1,000 BTU/h
• C1 square inch per 2,000 BTU/h
• D1 square inch per 5,000 BTU/h

When replacing an old 65% AFRI natural draft furnace with a 96% AFUE Category IV condensing furnace while leaving an existing 80% natural draft water heater connected to the masonry chimney, what code concern occurs?

• AThe water heater gas pressure spikes automatically to 14 in. w.c.
• BThe water heater becomes an 'orphaned' appliance, creating risk of flue gas condensation…
• CThe new furnace flue gas pressurizes the water heater burner pan
• DThe masonry chimney must be lined with copper tubing

What is the typical manifold pressure setting for low-fire operation on a two-stage Natural Gas residential furnace?

• A0.5 in. w.c.
• B1.7 to 1.8 in. w.c.
• C3.5 in. w.c.
• D5.0 in. w.c.

Per IMC Section 911, what safety interlock control must be installed on electric duct heaters to prevent element overheating in ductwork?

• AAn airflow proving switch (differential pressure switch or fan interlock relay)
• BA low-pressure refrigerant cutout switch
• CA humidity sensor set at 90%
• DA fusible link set at 500°F

A 230V single-phase compressor motor has a Full Load Amps (FLA) rating of 18.0 A. During startup, the Locked Rotor Amps (LRA) spike is typically how many times greater than the FLA rating?

• A1.2 to 1.5 times
• B2 to 3 times
• C5 to 7 times
• D12 to 15 times

How does a constant-airflow Electronically Commutated Motor (ECM) respond when duct static pressure increases due to a dirty air filter?

• AMotor RPM decreases automatically to protect the motor windings from overheating
• BMotor trips its internal thermal overload switch within 5 seconds
• CMotor increases RPM and power output to maintain design CFM
• DMotor switches from 230V operation down to 120V operation