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Question 1HVAC System Design, Load Calculation, and Equipment Selection

One ton of refrigeration capacity is equivalent to which rate of heat transfer?

  1. 12,000 Btu/h Correct answer.
  2. 3,413 Btu/h
  3. 200 Btu/h
  4. 1,000 Btu/h

Explanation

A ton of refrigeration is defined as the rate of heat removal needed to melt one ton of ice in 24 hours, which works out to 12,000 Btu/h. Equipment capacity and load calculations both use this same unit.

Question 2HVAC System Design, Load Calculation, and Equipment Selection

The sensible heat ratio (SHR) of a cooling load is defined as which of the following?

  1. Latent heat divided by sensible heat
  2. Sensible heat divided by the volume of the space
  3. Total heat divided by sensible heat
  4. Sensible heat divided by total heat Correct answer.

Explanation

SHR is the sensible portion of the total load, where total heat equals sensible plus latent heat. Its value always falls between 0 and 1 and indicates how much of the coil capacity goes toward lowering temperature versus removing moisture.

Question 3HVAC System Design, Load Calculation, and Equipment Selection

Approximately how much heat is released when one pound of water vapor condenses on a cooling coil?

  1. 144 Btu
  2. 1,060 Btu
  3. 970 Btu Correct answer.
  4. 8.33 Btu

Explanation

At the temperatures found across a typical evaporator coil, the latent heat of condensation is about 1,060 Btu per pound in most tables, and about 970 Btu per pound near the normal boiling point. Either value rounds to roughly 1,000 Btu per pound, which is why roughly 1,000 Btu/h of latent capacity corresponds to about one pound of moisture per hour.

Question 4HVAC System Design, Load Calculation, and Equipment Selection

The U-factor of a building assembly is which of the following?

  1. The thickness of insulation divided by its conductivity
  2. The sum of the layer R-values
  3. The rate of air leakage through the assembly
  4. The reciprocal of the assembly R-value Correct answer.

Explanation

U-factor is the overall conductance of an assembly and equals 1 divided by the total R-value. It is used directly with area and temperature difference to compute transmission heat flow.

Question 5HVAC System Design, Load Calculation, and Equipment Selection

The AFUE rating of a gas furnace expresses which of the following?

  1. Steady-state combustion efficiency measured at full firing rate only
  2. Ratio of rated input Btu to rated output Btu
  3. Seasonal useful heat output divided by seasonal fuel input Correct answer.
  4. Maximum allowable flue-gas temperature at rated input

Explanation

AFUE is an annual fuel utilization efficiency that accounts for steady-state losses plus cycling, jacket, and off-cycle losses over a heating season. It is always lower than the steady-state combustion efficiency of the same appliance.

Question 6HVAC System Design, Load Calculation, and Equipment Selection

Residential load calculations typically use a summer design dry-bulb temperature that is exceeded during approximately what share of the cooling season hours?

  1. 1% Correct answer.
  2. 5%
  3. 0.4%
  4. 10%

Explanation

Residential practice uses 1 percent summer design conditions and 99 percent winter design conditions, meaning the design temperature is exceeded about 1 percent of the annual hours in that season. Sizing to a rarer condition adds capacity that is almost never used.

Question 7HVAC System Design, Load Calculation, and Equipment Selection

Static pressure in residential duct systems is normally expressed in which unit?

  1. Inches of mercury
  2. Inches of water column Correct answer.
  3. Feet of head
  4. Pounds per square inch

Explanation

Duct pressures are small, so they are measured in inches of water column, where 1 in. w.c. equals about 0.036 psi. A typical residential blower is rated at about 0.5 in. w.c. total external static pressure.

Question 8HVAC System Design, Load Calculation, and Equipment Selection

A space has a sensible cooling load of 24,000 Btu/h, and the supply air is delivered 20°F below room temperature. Using the sensible heat equation with a factor of 1.08, what supply airflow is required?

  1. 1,000 cfm
  2. 556 cfm
  3. 2,222 cfm
  4. 1,111 cfm Correct answer.

Explanation

The sensible equation is Btu/h = 1.08 x cfm x temperature difference, so cfm equals 24,000 divided by (1.08 x 20). That gives about 1,111 cfm of supply air.

Question 9HVAC System Design, Load Calculation, and Equipment Selection

A furnace with a rated output of 60,000 Btu/h delivers 1,000 cfm. Using the 1.08 factor, what air temperature rise should be expected?

  1. 50°F
  2. 56°F Correct answer.
  3. 45°F
  4. 65°F

Explanation

Temperature rise equals Btu/h divided by (1.08 x cfm), so 60,000 divided by 1,080 gives about 56°F. The result should be compared with the manufacturer's listed rise range to confirm the blower setting is acceptable.

Question 10HVAC System Design, Load Calculation, and Equipment Selection

Supply ducts are routed through a 130°F attic in a hot climate. How should this be handled in the cooling load calculation?

  1. Add the calculated duct gain to the space load Correct answer.
  2. Ignore it if the ducts are insulated to R-8
  3. Add only the duct leakage to the load
  4. Assume it is offset by duct heat loss in winter

Explanation

Heat picked up by supply air in an unconditioned attic must be added to the coil load, either through a calculated value or an accepted default percentage. Insulation reduces but does not eliminate the gain, because the attic air is well above the supply air temperature.

Question 11HVAC System Design, Load Calculation, and Equipment Selection

In the ACCA residential design process, Manual S is used to do which of the following?

  1. Calculate room-by-room heating and cooling loads for the dwelling
  2. Size the duct system using the available external static pressure
  3. Match equipment capacity to the calculated loads using rating data Correct answer.
  4. Determine the required whole-house ventilation airflow rate

Explanation

Manual S is the equipment selection procedure; it compares the calculated loads from Manual J against expanded manufacturer performance data at the design conditions. It confirms that the selected unit meets both the sensible and latent load at the actual entering conditions.

Question 12HVAC System Design, Load Calculation, and Equipment Selection

A single-stage air conditioner is selected at 40 percent above the calculated load. What is the most likely result?

  1. Improved humidity control because the coil runs colder
  2. Reduced equipment cost with no effect on comfort
  3. Longer run times and better dehumidification
  4. Frequent short cycling with higher indoor humidity Correct answer.

Explanation

An oversized unit reaches the thermostat setpoint before the coil has run long enough to remove design moisture, so it cycles on and off. The space temperature is met while the latent load is left partly unmet, raising indoor relative humidity.

Question 13HVAC System Design, Load Calculation, and Equipment Selection

The balance point of an air-source heat pump is the outdoor temperature at which which of the following is true?

  1. The compressor locks out and only auxiliary heat runs
  2. Heating capacity equals the building heating load Correct answer.
  3. The outdoor coil must go into defrost
  4. The coefficient of performance equals 1.0

Explanation

Heat pump capacity falls as outdoor temperature drops while building load rises; where the two curves cross is the balance point. Below that temperature the unit needs supplemental heat to keep the space at setpoint.

Question 14HVAC System Design, Load Calculation, and Equipment Selection

Which statement describes emergency heat mode on a heat pump thermostat?

  1. It runs the compressor and resistance heaters together
  2. It reverses the reversing valve to defrost the outdoor coil
  3. It locks out the compressor and uses only the resistance heaters Correct answer.
  4. It raises indoor blower speed to increase delivered capacity

Explanation

Emergency heat is selected manually when the compressor is disabled or has failed, so the resistance heaters carry the entire load. In normal operation the resistance heaters serve as auxiliary or supplemental heat and run together with the compressor.

Question 15HVAC System Design, Load Calculation, and Equipment Selection

Whole-house mechanical ventilation under ASHRAE Standard 62.2 is sized primarily from which inputs?

  1. Conditioned volume and number of occupants
  2. Window area and measured infiltration rate
  3. Floor area and number of bedrooms Correct answer.
  4. Number of bathrooms and kitchen exhaust cfm

Explanation

The standard uses a formula combining the number of bedrooms, which estimates occupancy, with the conditioned floor area. The resulting whole-house rate is then met by a continuous or intermittent ventilation system.

Question 16HVAC System Design, Load Calculation, and Equipment Selection

Residential duct systems are commonly laid out using which design friction rate?

  1. 0.1 in. w.c. per 100 ft of equivalent length Correct answer.
  2. 0.5 in. w.c. per 100 ft of equivalent length
  3. 1.0 in. w.c. per 100 ft of equivalent length
  4. 0.02 in. w.c. per 100 ft of equivalent length

Explanation

About 0.1 in. w.c. per 100 ft of effective length is the traditional residential target and is often used as a starting point. Manual D instead derives the friction rate from the available static pressure divided into the total effective length of the longest run.

Question 17HVAC System Design, Load Calculation, and Equipment Selection

Bedroom doors are kept closed, and the bedrooms have supply registers but no return or transfer path. What is the correct remedy?

  1. Seal the bedroom doors tightly to stop the pressure difference
  2. Install transfer grilles or return grilles in each bedroom Correct answer.
  3. Reduce the system fan speed to lower the pressure
  4. Increase the size of the supply register in each bedroom

Explanation

A closed door with no return path lets the bedroom pressurize, which reduces supply airflow and forces air out through the envelope. A transfer grille, jump duct, or individual return equalizes pressure and restores the designed airflow.

Question 18HVAC System Design, Load Calculation, and Equipment Selection

A coil removes 30 pounds of water per hour. Using 1,060 Btu per pound, what is the latent capacity?

  1. 10,600 Btu/h
  2. 31,800 Btu/h Correct answer.
  3. 3,180 Btu/h
  4. 63,600 Btu/h

Explanation

Latent capacity is the mass of moisture removed per hour multiplied by the latent heat per pound, so 30 x 1,060 equals about 31,800 Btu/h. The same result can be checked with the 0.68 airflow-grains equation.

Question 19HVAC System Design, Load Calculation, and Equipment Selection

Which indoor design condition is commonly assumed for residential cooling load calculations?

  1. 72°F dry-bulb and 60% relative humidity
  2. 80°F dry-bulb and 65% relative humidity
  3. 75°F dry-bulb and 50% relative humidity Correct answer.
  4. 68°F dry-bulb and 30% relative humidity

Explanation

The residential default indoor cooling condition is 75°F dry-bulb at about 50 percent relative humidity, which keeps the space near 63°F dew point. Winter heating design typically uses 70°F indoor dry-bulb.

Question 20HVAC System Design, Load Calculation, and Equipment Selection

A coil is selected at an SHR of 0.85 for a space whose load SHR is 0.75. What is the expected result?

  1. Space sensible temperature cannot be maintained
  2. Indoor relative humidity will run higher than design Correct answer.
  3. Indoor relative humidity will run lower than design
  4. The compressor will short cycle on the low-pressure control

Explanation

The coil SHR must be equal to or lower than the space SHR so the coil removes at least as much moisture as the space produces. With a higher coil SHR, the moisture balance is not met and indoor humidity drifts upward.

Question 21HVAC System Design, Load Calculation, and Equipment Selection

A furnace blower is rated 1,200 cfm at 0.5 in. w.c. external static pressure, but the installed duct system imposes 0.8 in. w.c. What is the expected effect?

  1. Airflow drops, raising the temperature rise and overheating risk Correct answer.
  2. Airflow will increase because the blower speeds up
  3. The motor horsepower requirement stays constant regardless of static pressure
  4. Airflow will remain the same but the temperature rise will fall

Explanation

For a given blower speed, airflow falls as external static pressure rises, so the delivered cfm will be below the rating point. Lower airflow with the same heat input raises the temperature rise and can trip the high-limit switch.

Question 22HVAC System Design, Load Calculation, and Equipment Selection

A single-speed system serves three zones with a bypass damper. What does the bypass damper do when only one small zone is calling?

  1. It prevents the zone dampers from leaking air past their blades
  2. It increases compressor capacity to match the calling zone
  3. It lowers the supply air temperature to prevent duct condensation
  4. It relieves excess static pressure by bypassing air to the return Correct answer.

Explanation

When most zone dampers close, system airflow is restricted and static pressure rises toward the blower's shutoff point. A bypass damper diverts excess supply air back to the return to hold static pressure and evaporator airflow within safe limits.

Question 23HVAC System Design, Load Calculation, and Equipment Selection

In a dual-fuel system, the economic balance point is which temperature?

  1. Where the heat pump COP drops below 1.0
  2. Where heat pump cost per Btu equals furnace cost per Btu Correct answer.
  3. Where the heat pump capacity equals the building heating load
  4. The lowest outdoor temperature in the manufacturer's rating table

Explanation

The economic balance point sets the changeover temperature by comparing the delivered cost per Btu of the heat pump, including its defrost and capacity effects, with that of the fossil-fuel appliance. It depends on utility rates and equipment efficiencies, so it differs from the thermal balance point.

Question 24HVAC System Design, Load Calculation, and Equipment Selection

Blower heat and supply duct gain add heat to the airstream after the coil. How does this affect coil selection compared with the space load alone?

  1. The coil must be selected for a larger sensible load than the space load Correct answer.
  2. Duct and fan heat cancel out, so the space load is used directly
  3. Supply air temperature rises, so less airflow is required
  4. Blower heat reduces the coil load, so a smaller unit can be selected

Explanation

Fan heat and duct gain occur downstream of the coil, so the coil must cool the air to a lower temperature to meet the room condition. The result is a greater coil sensible load and a higher system SHR than the space SHR.

Question 25Refrigeration Cycle, Components, and Refrigerants

In a basic vapor-compression refrigeration cycle, what is the correct sequence of components?

  1. Compressor, evaporator, condenser, metering device
  2. Compressor, condenser, metering device, evaporator Correct answer.
  3. Condenser, compressor, evaporator, metering device
  4. Evaporator, compressor, metering device, condenser

Explanation

The compressor raises pressure and moves vapor to the condenser, where heat is rejected and the refrigerant liquefies. The liquid then passes through the metering device, which lowers pressure before it enters the evaporator. The evaporator absorbs heat and returns vapor to the compressor.

Question 26Refrigeration Cycle, Components, and Refrigerants

What is the primary function of the compressor in a refrigeration system?

  1. It lowers refrigerant pressure before the evaporator.
  2. It raises refrigerant pressure and temperature. Correct answer.
  3. It removes heat from the indoor air stream.
  4. It stores liquid refrigerant for the cooling season.

Explanation

The compressor takes low-pressure vapor from the evaporator and raises its pressure and temperature so heat can be rejected at the condenser. It also maintains the pressure difference that drives refrigerant flow through the cycle. Lowering pressure is the metering device's job, not the compressor's.

Question 27Refrigeration Cycle, Components, and Refrigerants

What happens to the refrigerant in the condenser?

  1. It rejects heat and condenses into a liquid. Correct answer.
  2. It absorbs heat and boils into a vapor.
  3. It is compressed to a higher discharge pressure.
  4. It drops in pressure through a fixed orifice.

Explanation

In the condenser, high-pressure superheated vapor gives up heat to the surrounding air or water and changes phase to a liquid. This heat rejection is what allows the cycle to move absorbed heat outdoors. Pressure reduction happens later at the metering device.

Question 28Refrigeration Cycle, Components, and Refrigerants

What is the purpose of the metering device?

  1. It raises the pressure of the vapor leaving the evaporator.
  2. It removes moisture from the refrigerant charge.
  3. It separates liquid from vapor before the compressor.
  4. It drops pressure and controls flow to the evaporator. Correct answer.

Explanation

The metering device creates the pressure difference between the high side and low side and regulates how much liquid refrigerant enters the evaporator. This pressure drop causes the refrigerant to flash and cool before absorbing heat. Raising pressure is the compressor's role.

Question 29Refrigeration Cycle, Components, and Refrigerants

In the evaporator, the refrigerant typically:

  1. passes through a filter drier before expanding.
  2. absorbs heat from the space and boils. Correct answer.
  3. rejects heat to the outdoor air and condenses.
  4. is compressed to a higher temperature.

Explanation

Low-pressure liquid refrigerant enters the evaporator and absorbs heat from the surrounding air or product. That heat causes the liquid to boil into vapor, producing the cooling effect. Condensing and rejecting heat occur at the condenser.

Question 30Refrigeration Cycle, Components, and Refrigerants

Superheat is defined as the temperature of refrigerant vapor:

  1. equal to its saturation temperature at the same pressure.
  2. above its saturation temperature at the same pressure. Correct answer.
  3. below its saturation temperature at the same pressure.
  4. measured only at the condenser outlet.

Explanation

Superheat is the number of degrees a vapor is heated above its saturation temperature at a given pressure. It confirms that no liquid droplets remain at the measuring point. A temperature equal to saturation is the saturated condition itself, not superheat.

Question 31Refrigeration Cycle, Components, and Refrigerants

Most of the cooling effect in an evaporator comes from:

  1. the compressor adding heat to the refrigerant.
  2. sensible heat removed as the refrigerant warms.
  3. subcooling the liquid before the metering device.
  4. latent heat absorbed as liquid refrigerant boils. Correct answer.

Explanation

The largest portion of heat absorption occurs when liquid refrigerant changes phase to vapor inside the evaporator. This latent heat transfer occurs without a large temperature change in the refrigerant. Sensible heat gain by the vapor accounts for a much smaller share.

Question 32Refrigeration Cycle, Components, and Refrigerants

At the compressor discharge, the refrigerant should be:

  1. a saturated liquid-vapor mixture.
  2. a two-phase mixture at low pressure.
  3. a subcooled liquid.
  4. a superheated vapor. Correct answer.

Explanation

The compressor takes in vapor and compresses it, so the discharge is always superheated vapor. This superheat protects the compressor from slugging and allows heat rejection in the condenser. Liquid at the discharge would indicate a serious system problem.

Question 33Refrigeration Cycle, Components, and Refrigerants

Subcooling is the number of degrees the liquid refrigerant is:

  1. heated above its saturation temperature at the same pressure.
  2. below the evaporator coil temperature.
  3. cooled below its saturation temperature at the same pressure. Correct answer.
  4. warmer than the ambient air around the condenser.

Explanation

Subcooling measures how far liquid refrigerant has been cooled below its saturation temperature at the existing pressure. It indicates that the condenser has fully liquefied the refrigerant and provided a solid column of liquid to the metering device. Superheat is the corresponding term for vapor.

Question 34Refrigeration Cycle, Components, and Refrigerants

A thermostatic expansion valve (TXV) maintains constant superheat by:

  1. modulating flow in response to bulb pressure. Correct answer.
  2. cycling the compressor on and off.
  3. holding the evaporator pressure at a fixed value.
  4. bypassing hot gas directly into the evaporator.

Explanation

The TXV senses evaporator outlet temperature with a remote bulb and balances bulb pressure against evaporator pressure and spring force. This balance moves the valve stem to increase or decrease refrigerant flow and hold superheat near the set point. The valve modulates continuously rather than simply opening or closing.

Question 35Refrigeration Cycle, Components, and Refrigerants

Which statement describes a capillary tube metering device?

  1. It uses a solenoid to open and close on each cycle.
  2. It adjusts flow automatically as load changes.
  3. It is a fixed restriction that does not adjust. Correct answer.
  4. It has a movable needle controlled by a remote bulb.

Explanation

A capillary tube is a small-diameter tube that provides a fixed pressure drop and flow rate. Because it has no moving parts, it cannot adjust to changing load conditions the way a TXV can. System charge and tube length are matched to the appliance's design conditions.

Question 36Refrigeration Cycle, Components, and Refrigerants

R-410A differs from R-22 mainly because R-410A:

  1. is a blend that operates at higher pressures. Correct answer.
  2. can be used with mineral oil without any changes.
  3. operates at lower pressures and is not a blend.
  4. is a single-component refrigerant with no glide.

Explanation

R-410A is a near-azeotropic blend of R-32 and R-125 that operates at pressures roughly 50 to 60 percent higher than R-22. It also requires polyolester oil because mineral oil is not miscible with HFC refrigerants. Equipment and gauges must be rated for the higher pressures.

Question 37Refrigeration Cycle, Components, and Refrigerants

R-22 is classified as which type of refrigerant, and what is its regulatory status?

  1. A CFC that was banned in the 1990s.
  2. A natural refrigerant exempt from regulation.
  3. An HFC with no phase-out schedule.
  4. An HCFC being phased out by international treaty. Correct answer.

Explanation

R-22 is a hydrochlorofluorocarbon (HCFC) controlled under the Montreal Protocol because it depletes stratospheric ozone. Its production and import have been phased out, and only reclaimed or stockpiled supplies remain for service. CFCs such as R-12 were phased out earlier.

Question 38Refrigeration Cycle, Components, and Refrigerants

Continuous bubbles in a liquid-line sight glass most likely indicate:

  1. the system is overcharged with refrigerant.
  2. the compressor is operating at too low a discharge pressure.
  3. a shortage of refrigerant or a restriction. Correct answer.
  4. the condenser is rejecting too much heat.

Explanation

Bubbles in the sight glass mean flash gas is present in the liquid line, which usually points to an undercharge or a restriction such as a clogged filter drier. A clear glass indicates solid liquid at that point. Overcharging normally produces a full liquid line rather than continuous bubbles.

Question 39Refrigeration Cycle, Components, and Refrigerants

What is the purpose of a suction accumulator?

  1. It stores liquid refrigerant for the heating season.
  2. It keeps liquid refrigerant out of the compressor. Correct answer.
  3. It removes moisture and acid from the refrigerant.
  4. It increases the pressure of suction vapor.

Explanation

A suction accumulator is installed in the suction line to trap liquid refrigerant and allow it to boil off before reaching the compressor. This protects the compressor from slugging and oil dilution. It does not filter or raise pressure.

Question 40Refrigeration Cycle, Components, and Refrigerants

A crankcase heater is used to:

  1. prevent refrigerant migration into the compressor oil. Correct answer.
  2. warm the evaporator coil during defrost.
  3. heat the suction line to increase superheat.
  4. raise the discharge temperature of the compressor.

Explanation

The crankcase heater warms compressor oil so refrigerant that has migrated during the off cycle does not condense and dilute the oil. This helps maintain lubrication at startup and reduces the risk of slugging. It is not intended to affect superheat or defrost.

Question 41Refrigeration Cycle, Components, and Refrigerants

When evacuating a refrigeration system, a typical target is:

  1. 5,000 microns and holding.
  2. 500 microns and holding. Correct answer.
  3. atmospheric pressure.
  4. 29 inches of mercury on a gauge.

Explanation

A deep vacuum of about 500 microns removes moisture and noncondensable gases from the system. The vacuum should hold after the pump is isolated to confirm there are no leaks or trapped moisture. A gauge reading of 29 inches of mercury is not a reliable deep-vacuum measurement.

Question 42Refrigeration Cycle, Components, and Refrigerants

For a system with a fixed orifice metering device, the charge is normally adjusted by:

  1. measuring superheat at the evaporator outlet. Correct answer.
  2. charging until the sight glass is clear.
  3. setting subcooling to 10°F.
  4. adding refrigerant until the suction pressure stops rising.

Explanation

Fixed-orifice systems are charged by superheat because the orifice cannot compensate for charge variations the way a TXV can. The measured superheat is compared with the manufacturer's chart for the indoor and outdoor conditions. TXV systems are typically charged by subcooling instead.

Question 43Refrigeration Cycle, Components, and Refrigerants

A scroll compressor is characterized by:

  1. two intermeshing spiral scrolls, one orbiting. Correct answer.
  2. a single rotating vane in a cylindrical housing.
  3. a piston driven by a connecting rod.
  4. a centrifugal impeller that raises pressure.

Explanation

A scroll compressor uses two spiral-shaped scrolls; one remains fixed while the other orbits to trap and compress refrigerant vapor. It has few moving parts and operates with continuous suction and discharge. Pistons, vanes, and impellers describe other compressor types.

Question 44Refrigeration Cycle, Components, and Refrigerants

A zeotropic refrigerant blend has a temperature glide, which means:

  1. it must be charged as a liquid only.
  2. it boils and condenses at a single constant temperature.
  3. its components separate permanently during use.
  4. its saturation temperature changes as it evaporates. Correct answer.

Explanation

In a zeotropic blend, the components have different boiling points, so the saturation temperature changes as the mixture evaporates or condenses. This temperature glide must be accounted for when measuring superheat and subcooling. A single constant boiling temperature describes an azeotrope.

Question 45Refrigeration Cycle, Components, and Refrigerants

On a pressure-enthalpy diagram, the refrigerating effect per pound of refrigerant is:

  1. the enthalpy difference between evaporator outlet and inlet. Correct answer.
  2. the enthalpy difference between condenser inlet and outlet.
  3. the enthalpy difference between compressor discharge and suction.
  4. the pressure difference across the metering device.

Explanation

Refrigerating effect is the heat absorbed per pound of refrigerant as it passes through the evaporator, found from the enthalpy change across that coil. It is not the compressor work or the condenser heat rejection. Pressure difference is a separate operating parameter.

Question 46Refrigeration Cycle, Components, and Refrigerants

A system has a suction pressure of 70 psig and a discharge pressure of 210 psig. Using absolute pressures, what is the compression ratio?

  1. About 3.5 to 1
  2. About 3.0 to 1
  3. About 1.5 to 1
  4. About 2.6 to 1 Correct answer.

Explanation

Add atmospheric pressure to each gauge reading: 70 + 14.7 = 84.7 psia and 210 + 14.7 = 224.7 psia. Dividing discharge by suction gives about 2.65, or roughly 2.6 to 1. Using gauge pressures directly would give an incorrect ratio.

Question 47Refrigeration Cycle, Components, and Refrigerants

When retrofitting an R-22 system to an HFC refrigerant such as R-407C, the mineral oil typically must be replaced with:

  1. a castor-based lubricant.
  2. no lubricant at all.
  3. polyolester (POE) oil. Correct answer.
  4. a silicone-based lubricant.

Explanation

HFC refrigerants are not sufficiently miscible with mineral oil, so POE oil is used to ensure lubrication returns through the system. Retrofits usually require flushing or multiple oil changes to remove the old mineral oil. Silicone and castor oils are not suitable compressor lubricants for this application.

Question 48Refrigeration Cycle, Components, and Refrigerants

Under EPA Section 608, appliances containing 5 or more pounds of refrigerant must:

  1. be leak-inspected only if the owner requests it.
  2. repair leaks after exceeding the leak rate limit. Correct answer.
  3. be vented to the atmosphere before service.
  4. use only CFC refrigerants.

Explanation

Section 608 sets leak rate thresholds by appliance type, and once an appliance exceeds its threshold the owner must have leaks repaired within a specified time and verify the repair. Recordkeeping and follow-up verification are also required. Venting refrigerant to the atmosphere is prohibited.

Question 49Heating Equipment and Systems (Furnaces, Boilers, Heat Pumps)

The AFUE rating posted on a furnace represents:

  1. The ratio of delivered heat to blower electrical energy consumed
  2. The maximum steady-state combustion efficiency at full firing rate
  3. The total heat output in Btu per hour at the rated input
  4. The percentage of the fuel's energy delivered as heat over a typical heating season Correct answer.

Explanation

AFUE compares the total useful heat delivered over a heating season with the total energy content of the fuel consumed, including cycling and off-cycle losses. It is an annual efficiency percentage, not a capacity or steady-state combustion figure.

Question 50Heating Equipment and Systems (Furnaces, Boilers, Heat Pumps)

In a standing-pilot gas furnace, the thermocouple functions to:

  1. Generate a small voltage that holds the gas valve open while the pilot flame is proven Correct answer.
  2. Limit manifold gas pressure to 3.5 in. w.c.
  3. Step line voltage down to 24 volts for the gas valve
  4. Sense flue-gas temperature and start the blower

Explanation

A thermocouple heated by the pilot flame produces a few millivolts, which the gas valve uses as a safety signal to stay open. If the pilot goes out, the voltage disappears and the valve closes.