Arizona ROC C-79/CR-79/R-39 Air Conditioning and Refrigeration Including Solar Examination

A commercial flat-plate solar thermal collector array receives an average solar irradiance of 300 BTU/h·ft². The collectors have a total surface area of 400 ft² and deliver heat to a fluid loop where the entering fluid temperature is 110°F, leaving temperature is 140°F, and flow rate is 4.8 GPM of pure water. What is the thermal efficiency of the solar collector array?

• A50.0%
• B60.0%
• C70.0%
• D80.0%

When calibrating a differential temperature controller for a solar thermal forced-circulation hydronic heating loop, what is the standard recommended collector-to-tank temperature differential (ΔT) to start the solar circulating pump (cut-in setpoint)?

• A2°F to 4°F
• B8°F to 20°F
• C30°F to 45°F
• D50°F to 65°F

An HVAC solar contractor is installing an active closed-loop solar thermal system in northern Arizona. What concentration of uninhibited or inhibited USP propylene glycol in water is required to provide freeze protection down to -28°F?

• A10% propylene glycol / 90% water
• B25% propylene glycol / 75% water
• C50% propylene glycol / 50% water
• D85% propylene glycol / 15% water

During a summer power outage in Phoenix, Arizona, a high-efficiency glazed flat-plate solar collector array enters a stagnation condition (zero fluid circulation under full sunlight). What internal absorber temperature can these collectors reach?

• A160°F to 180°F
• B200°F to 220°F
• C350°F to 400°F
• D600°F to 750°F

A closed solar thermal collector loop contains 30 gallons of 50% propylene glycol solution. The system operates between a cold fill temperature of 60°F (fill pressure 30 psig) and a maximum operating temperature of 210°F (relief valve set at 75 psig). Given fluid thermal expansion of 5.5%, what is the minimum required total acceptance volume of the solar expansion tank?

• A0.85 gallons
• B1.65 gallons
• C3.50 gallons
• D6.20 gallons

In a solar thermal drainback HVAC system, all solar piping between the outdoor roof collectors and the indoor drainback reservoir tank must be installed with a continuous downward slope. What is the minimum required pitch per foot of pipe run according to solar piping standards?

• A1/16 inch per foot
• B1/8 inch per foot
• C1/4 inch per foot
• D1/2 inch per foot

According to the International Mechanical Code (IMC) and Plumbing Code (IPC), when a solar thermal loop containing toxic chemical additives (such as ethylene glycol or chemical corrosion inhibitors) transfers heat to a potable water heating system, what type of heat exchanger MUST be used?

• ASingle-wall heat exchanger with automatic water makeup
• BDouble-wall heat exchanger with a vented intermediate air space
• CDirect immersion bare copper coil without separation
• DCounter-flow single-wall plate heat exchanger with check valves

Because solar water heating storage tanks can reach temperatures well in excess of 160°F on bright summer days, what device must be installed on the domestic hot water supply line leaving the solar storage tank to prevent scalding?

• APressure reducing valve (PRV)
• BASSE 1017 thermostatic mixing valve
• CTemperature-actuated solenoid valve
• DFlow limiting orifice disc

A solar-assisted absorption air conditioning system utilizes a single-effect lithium bromide-water (LiBr-H2O) absorption chiller. What minimum hot water generator fluid supply temperature is required from the solar collector array for effective chiller operation?

• A110°F to 125°F
• B170°F to 195°F
• C260°F to 300°F
• D400°F to 450°F

Where should a microbubble air eliminator / air separator be installed in a closed-loop hydronic solar thermal system for optimum air removal performance?

• AAt the lowest point of the system return line entering the storage tank
• BAt the point of highest fluid temperature and lowest pressure (suction side of pump)
• COn the high-pressure discharge piping leaving the circulator pump
• DInside the expansion tank bladder connection

When plumbing a large commercial solar collector array consisting of eight flat-plate collectors mounted side-by-side in parallel, why is reverse-return header piping strongly specified over direct-return piping?

• AIt reduces total copper pipe footage required for the roof installation
• BIt ensures equal pipe path length and uniform flow distribution through all collectors wi…
• CIt eliminates the need for pipe thermal insulation on the return header
• DIt prevents thermal shock when cold water enters the first collector in the string

Why must a atmospheric vacuum relief valve (vacuum breaker) be installed at the high point of a solar thermal drainback collector array?

• ATo prevent air from entering the system during normal operation
• BTo allow air to enter the top of the array when the pump turns off, breaking the fluid si…
• CTo relieve excess fluid pressure during peak summer stagnation
• DTo equalize collector pressure with the refrigerant suction line

When joining copper tubing for high-temperature closed-loop solar thermal collector lines subject to stagnation temperatures over 300°F, which joining method is required by mechanical trade standards?

• A50/50 Lead-Tin soft solder
• B95/5 Tin-Antimony soft solder
• CHigh-temperature silver brazing alloy (minimum 15% silver or AWS BCuP/BAg classification)
• DStandard push-to-connect O-ring fittings

For a year-round solar thermal space heating and domestic hot water system installed in Phoenix, Arizona (latitude approximately 33°N), what collector tilt angle relative to the horizontal is ideal for maximizing overall annual solar energy collection?

• A10°
• B33° (Equal to local latitude)
• C65°
• D90° (Vertical wall)

What happens to propylene glycol heat transfer fluid in a closed solar loop if it is repeatedly subjected to high stagnation temperatures exceeding 320°F without fluid relief or cooling?

• AThe fluid turns into pure distilled water
• BThe glycol oxidizes into acidic byproducts (organic acids), dropping pH below 7.0 and cau…
• CThe fluid permanently freezes at room temperature
• DThe viscosity drops to zero, increasing pump flow rate by 300%

An HVAC heat pump system is equipped with a solar-assisted desuperheater heat exchanger. During summer compressor operation, where does the desuperheater reject superheat energy?

• ADirectly into the indoor supply air ductwork
• BInto a domestic hot water preheat storage tank
• CBack into the compressor crankcase oil sump
• DOut through the outdoor solar collector absorber plate

Per IMC Chapter 14 and ASME standards, what requirement applies to the discharge piping connected to an ASME pressure relief valve installed on a closed solar thermal system?

• AIt must discharge directly into the domestic fresh water tank
• BIt must terminate independently to an approved location or catch tank, sloped downward, w…
• CIt must be capped with a threaded iron plug to prevent fluid leakage
• DIt must connect directly to the refrigerant suction line

Where must the collector temperature sensor for a solar differential controller be physically located for accurate pump control?

• AIn the ambient air underneath the collector mounting frame
• BThermally bonded to the absorber plate or outlet header inside the collector enclosure wi…
• COn the cold fluid inlet pipe entering the bottom of the collector array
• DInside the indoor expansion tank air chamber

In North America (including Arizona), towards which compass direction should fixed solar thermal collectors be oriented for maximum daily solar radiation collection?

• ATrue North
• BTrue South (or magnetic south adjusted for compass declination)
• CDue East
• DDue West

When mounting roof-integrated solar thermal collector frames in Arizona, what minimum design wind uplift load standard must structural mounts withstand according to IBC / ASCE 7 rules for typical residential roofs?

• A10 mph wind velocity equivalent
• BDesign wind speeds of 105 mph to 115 mph (uplift pressures engineered per roof zone)
• C300 mph tornado rating
• DNo wind load requirement if lag screws are used

Under EPA Section 608 regulations, what is the annual leak rate threshold that triggers mandatory repair for commercial refrigeration equipment containing 50 or more pounds of ODS refrigerant?

• A10%
• B20%
• C30%
• D50%

An HVAC technician measures a liquid line pressure of 334 psig on an R-410A system (saturated condensing temperature = 104°F). The measured liquid line temperature at the condenser outlet is 92°F. What is the system subcooling?

• A6°F
• B12°F
• C18°F
• D24°F

A walk-in freezer operating on R-404A has a suction gauge pressure of 30 psig (saturated evaporator temperature = -14°F). The measured suction line temperature near the TEV bulb is 4°F. What is the evaporator superheat?

• A10°F
• B18°F
• C26°F
• D34°F

When using recovery equipment manufactured AFTER November 15, 1993, to recover HCFC-22 from a medium-pressure appliance containing less than 200 pounds of refrigerant, to what level must the system be evacuated?

• A0 inches of Hg vacuum (0 psig)
• B4 inches of Hg vacuum
• C10 inches of Hg vacuum
• D15 inches of Hg vacuum

What deep vacuum micron level is required by industry standard practice (and equipment manufacturers) when evacuating a repaired HVAC-R system to ensure non-condensables and moisture are removed prior to charging?

• A5,000 microns
• B2,500 microns
• C500 microns or lower (holding steady)
• D50 microns absolute zero

What is the ASHRAE Standard 34 safety classification for R-32 and R-454B refrigerants currently replacing R-410A in residential and light commercial air conditioning systems?

• AA1 (Non-flammable, low toxicity)
• BA2L (Lower flammability, low toxicity)
• CA3 (Higher flammability, low toxicity)
• DB2 (Lower flammability, higher toxicity)

Where must the external equalizer line of an externally equalized Thermostatic Expansion Valve (TXV) be connected?

• ATo the liquid line upstream of the filter-drier
• BTo the suction line downstream of the sensing bulb
• CTo the suction line immediately downstream of the sensing bulb location
• DDirectly to the compressor oil sump return port

According to standard refrigeration design practices, a liquid receiver in a commercial refrigeration system must be sized to hold what maximum percentage of the total system refrigerant charge at 90°F liquid density?

• A50%
• B80%
• C100%
• D125%

When observing a liquid line sight glass / moisture indicator on an operating commercial refrigeration unit, what does a solid green color indicator with bubbles present in the liquid stream signify?

• AThe system is dry (no moisture), but liquid line subcooling is insufficient or system is…
• BThe system is flooded with liquid moisture and requires a filter-drier change
• CThe compressor oil level is critically low
• DNon-condensable air is trapped in the evaporator

Where is a hot gas bypass valve installed, and what is its primary function in a commercial refrigeration system?

• ABetween liquid line and suction line; to subcool liquid refrigerant
• BBetween compressor discharge line and evaporator inlet (after expansion valve); to preven…
• CBetween condenser and liquid receiver; to control head pressure
• DOn the oil equalizer line; to balance oil between dual compressors

How does a head pressure control valve (such as a Sporlan LAC valve) maintain liquid pressure in air-cooled refrigeration condensers during low ambient outdoor conditions in Arizona winter nights?

• AIt speeds up the outdoor condenser fan motor
• BIt backs up liquid refrigerant inside the condenser coil to reduce effective condensing s…
• CIt opens a water regulating valve to cool the liquid receiver
• DIt shuts off the compressor until outdoor temperature rises above 70°F

What procedure must an HVAC technician follow per EPA regulations before scrapping a disposable DOT-39 non-refillable refrigerant cylinder?

• AFill the cylinder with water and seal the valve tightly
• BRecover all remaining refrigerant down to 0 psig (or vacuum), render the cylinder unusabl…
• CVenting the remaining gas to atmosphere if under 5 lbs
• DRe-filling the cylinder with nitrogen to 150 psig before disposal

Where is an oil separator installed in a low-temperature commercial refrigeration system, and how does it return oil to the compressor?

• AOn the suction line; returns oil through a metering orifice to the expansion valve
• BOn the discharge line near the compressor; collects oil droplets and returns oil via a fl…
• COn the liquid line after the drier; feeds oil directly into the evaporator coil
• DInside the liquid receiver; drains oil out the bottom waste valve

What distinct operating characteristic distinguishes R-744 (Carbon Dioxide) transcritical refrigeration systems from traditional R-410A or R-404A subcritical systems during warm ambient operations?

• ASystem high-side pressure operates above the critical point (87.8°F / 1055 psig), where g…
• BR-744 operates at sub-atmospheric vacuum pressures on the high side
• CR-744 requires mineral oil instead of synthetic POE lubricant
• DR-744 cannot function when outdoor temperatures exceed 60°F

What visual marking and valve thread specification feature distinguishes recovery and service cylinders dedicated to A2L mildly flammable refrigerants (e.g., R-32, R-454B)?

• AYellow cylinder with green top and standard right-hand threads
• BRed band / red shoulder paint marking and left-hand (LH) valve connection threads
• CBlue cylinder with white stripes and push-fit valve
• DBlack cylinder with stainless steel quick-connects

An HVAC technician is evaluating a split-system air conditioner. The measured total sensible cooling heat load is 32,400 BTU/h, and the temperature difference (ΔT) across the evaporator coil is 20°F. What total airflow (CFM) is the blower delivering?

• A1,200 CFM
• B1,500 CFM
• C1,800 CFM
• D2,100 CFM

An air conditioning system handles 2,000 CFM of air. The specific humidity ratio difference across the cooling coil is 0.003 lb of moisture per lb of dry air (equivalent to ΔW = 21 grains/lb). Using the latent heat constant formula Ql = 0.68 × CFM × ΔW (where ΔW is in grains/lb), what is the latent cooling load capacity?

• A14,280 BTU/h
• B28,560 BTU/h
• C42,840 BTU/h
• D57,120 BTU/h

An HVAC technician adjusts a belt-driven supply air fan pulley, increasing fan rotational speed from 800 RPM to 1,000 RPM. If the initial measured airflow was 4,000 CFM, what is the new airflow delivering to the space?

• A4,500 CFM
• B5,000 CFM
• C6,250 CFM
• D7,812 CFM

If a fan running at 800 RPM generates a duct static pressure of 0.80 inches water column (in. w.g.), what will be the new duct static pressure when fan speed is increased to 1,000 RPM?

• A1.00 in. w.g.
• B1.25 in. w.g.
• C1.56 in. w.g.
• D1.95 in. w.g.

What is the standard design friction rate per 100 feet of equivalent duct length commonly used for sizing low-velocity commercial supply air ductwork using the Equal Friction method?

• A0.01 in. w.g. per 100 ft
• B0.10 in. w.g. per 100 ft
• C0.50 in. w.g. per 100 ft
• D1.00 in. w.g. per 100 ft

What primary operational feature distinguishes a 3-pipe Variable Refrigerant Flow (VRF) heat recovery system from a standard 2-pipe VRF heat pump system?

• A3-pipe VRF allows simultaneous heating in some indoor zones while cooling other zones by…
• B3-pipe VRF uses water as the primary refrigerant inside the building lines
• C3-pipe VRF requires an external oil separator line run to each indoor unit
• D3-pipe VRF can only operate in cooling mode when outdoor temperature exceeds 100°F

In most standard residential air-source heat pumps (such as those using an 'O' thermostat terminal connection), what operational mode is the reversing valve 4-way solenoid in when DE-ENERGIZED?

• AHeating mode
• BCooling mode
• CDefrost mode
• DEmergency heat auxiliary mode

During a heat pump defrost cycle, what two automatic control actions occur simultaneously to clear ice from the outdoor coil while maintaining indoor comfort?

• AThe indoor blower shuts off and the outdoor fan speeds up to 100%
• BThe reversing valve shifts to cooling mode, the outdoor fan stops, and auxiliary electric…
• CThe compressor stops running and hot glycol sprays onto the outdoor coil
• DThe expansion valve opens 100% while the indoor fan runs in reverse

An HVAC technician measures return static pressure of -0.25 in. w.g. before the indoor blower inlet and supply static pressure of +0.35 in. w.g. after the indoor cooling coil outlet. What is the Total External Static Pressure (ESP) of the system?

• A0.10 in. w.g.
• B0.35 in. w.g.
• C0.60 in. w.g.
• D0.85 in. w.g.

In ACCA Manual J residential load calculations for low-desert Arizona homes, what window performance parameter measures the fraction of incident solar radiation admitted through glass?

• AU-Factor
• BSolar Heat Gain Coefficient (SHGC)
• CAir Infiltration Rate (CFM/ft²)
• DThermal Resistance (R-value)

On a psychrometric chart, what does a Sensible Heat Ratio (SHR) of 0.80 indicate for a rooftop packaged A/C unit?

• A80% of total cooling capacity removes sensible heat (lowering temperature) and 20% remove…
• B80% of cooling capacity goes to latent moisture removal and 20% to temperature reduction
• CThe system has an efficiency loss of 20%
• D80 CFM out of every 100 CFM bypasses the cooling coil