Arizona CR-79 Air Conditioning and Refrigeration Practice Test

Description

Sample Questions

Question 1. A technician is commissioning a split air-conditioning system. The suction pressure corresponds to a refrigerant saturation temperature of 40°F, while the suction line temperature measured near the evaporator outlet is 62°F. What is the evaporator outlet superheat?

A. 12°F
B. 18°F
C. 22°F
D. 32°F

Correct Answer: C. 22°F

Answer Explanation:

Option C is correct because superheat is calculated by subtracting the refrigerant’s saturation temperature at the measured suction pressure from the actual suction-line temperature. In this case, 62°F − 40°F = 22°F of superheat. This measurement helps technicians evaluate whether the evaporator is receiving an appropriate amount of refrigerant and whether liquid refrigerant may remain at the evaporator outlet. The significance of the reading depends on the equipment manufacturer’s specifications, metering device, operating load, and measurement location. A fixed superheat value is not appropriate for every system. Technicians should also confirm stable operating conditions and use the correct refrigerant pressure-temperature relationship before making adjustments.

Why the other options are incorrect:

Option A is incorrect because 12°F does not result from subtracting the stated saturation temperature from the measured line temperature.
Option B is incorrect because 18°F does not match the calculation using the supplied measurements.
Option D is incorrect because 32°F overstates the calculated superheat.

Quick Study Guide:

Superheat = actual suction-line temperature − saturation temperature.
Use suction pressure and the correct refrigerant pressure-temperature chart.
Compare the measured superheat with the manufacturer’s specifications.
Verify stable operating conditions before diagnosing refrigerant charge or metering-device problems.

Question 2. A technician services a single-phase air-conditioning compressor that hums briefly when the contactor closes and then trips its overload protector. The supply voltage is within the manufacturer’s specified range, the compressor terminals receive the correct voltage, and the compressor shaft is not mechanically seized. Testing reveals that the run capacitor is substantially below its rated capacitance. What is the most appropriate next step?

A. Replace the defective run capacitor with one matching the manufacturer’s specified capacitance and voltage rating, then retest the system.
B. Increase the circuit-breaker rating to prevent the compressor from tripping.
C. Add refrigerant until the suction pressure rises enough for the compressor to start.
D. Bypass the compressor overload protector and leave it disconnected during operation.

Correct Answer: A. Replace the defective run capacitor with one matching the manufacturer’s specified capacitance and voltage rating, then retest the system.

Answer Explanation:
Option A is correct because a failed or significantly weakened run capacitor can prevent a compatible single-phase compressor from developing the required running torque. The compressor may hum, draw excessive current, and trip its overload protector. The technician should isolate electrical power, verify that the capacitor is safely discharged, and confirm its capacitance using an appropriate meter. Replacement must match the manufacturer’s specified capacitance and meet the required voltage rating and component specifications. After replacement, the technician should verify operating current, starting behavior, and normal system performance. If the compressor still fails to operate, further diagnosis is necessary. A low capacitance reading is strong evidence of a defective capacitor, but it does not rule out additional electrical or mechanical faults.

Why the other options are incorrect:

Option B is incorrect because increasing breaker capacity without verifying circuit and equipment requirements can create a serious electrical hazard.
Option C is incorrect because adding refrigerant does not correct a defective capacitor and may introduce an additional system fault.
Option D is incorrect because bypassing the overload protector removes an important safety function and risks damaging the compressor.

Quick Study Guide:

A weak run capacitor can cause humming, failed starting, or excessive motor current.
Match replacement capacitance to the equipment specifications.
Disconnect power and safely discharge capacitors before testing.
Never bypass overload protection or increase breaker ratings to mask a fault.

Question 3. During a summer service call, an air-conditioning system runs continuously but provides little cooling. The technician observes frost developing across much of the evaporator coil. Measurements show low suction pressure, while inspection reveals a heavily clogged return-air filter and severely restricted airflow. What should the technician do first?

A. Add refrigerant immediately because low suction pressure always indicates an undercharged system.
B. Increase the thermostat setting to force more refrigerant through the evaporator.
C. Adjust the expansion valve to its maximum opening before correcting the airflow restriction.
D. Restore adequate airflow by replacing the clogged filter, inspect the evaporator, and allow any ice to thaw before reassessing system operation.

Correct Answer: D. Restore adequate airflow by replacing the clogged filter, inspect the evaporator, and allow any ice to thaw before reassessing system operation.

Answer Explanation:

Option D is correct because restricted airflow reduces the amount of heat transferred from return air to the evaporator refrigerant. The evaporator temperature can fall below freezing, allowing moisture to accumulate as ice. As ice builds, airflow may deteriorate further, reducing cooling capacity and lowering suction pressure. The technician should correct the filter restriction, inspect the blower and other airflow components, and allow the coil to thaw completely before evaluating refrigerant pressures under appropriate operating conditions. Operating with a heavily iced coil can produce misleading diagnostic readings and prolong poor performance. If freezing returns after airflow has been restored, additional investigation should consider refrigerant metering, refrigerant charge, blower performance, and other possible causes.

Why the other options are incorrect:

Option A is incorrect because low suction pressure can result from restricted airflow and does not independently prove an undercharge.
Option B is incorrect because changing the thermostat setting does not remove the airflow restriction or resolve existing coil ice.
Option C is incorrect because opening a metering device without establishing the cause can lead to improper refrigerant flow and additional problems.

Quick Study Guide:

Restricted evaporator airflow can cause low suction pressure and coil icing.
Check filters, blower operation, evaporator cleanliness, and airflow before adjusting refrigerant charge.
Thaw an iced coil completely before taking diagnostic measurements.
If icing persists, investigate additional refrigeration and airflow faults.

Question 4. A technician inspects a closed-loop solar thermal water-heating system that uses a glycol-based heat-transfer fluid. During periods of strong sunlight, the collector-loop pressure rises sharply, and the pressure-relief valve repeatedly discharges fluid as the system heats up. The system’s cold pressure is within specifications, and no evidence of a pipe blockage is found. Which component should receive particular attention?

A. The domestic hot-water outlet aerator.
B. The collector-loop expansion tank, including its sizing, precharge, and condition.
C. The solar collector glazing, because clear glazing directly increases loop pressure independently of fluid temperature.
D. The domestic hot-water thermostat, because lowering its setting eliminates the need for thermal expansion control in the collector loop.

Correct Answer: B. The collector-loop expansion tank, including its sizing, precharge, and condition.

Answer Explanation:
Option B is correct because glycol-based solar thermal systems experience substantial fluid-temperature changes as solar energy is collected. As the heat-transfer fluid warms, it expands. The expansion tank must accommodate this additional volume while keeping loop pressure within the system’s permitted operating range. An undersized tank, incorrect precharge, failed diaphragm, or loss of the tank’s gas charge can contribute to excessive pressure and repeated relief-valve discharge. The technician should follow the manufacturer’s procedures to check the tank and system safely, accounting for fluid temperature, static pressure, and specified precharge conditions. The cause must be corrected before the system is returned to service. Repeatedly resetting or replacing the relief valve alone will not resolve an underlying expansion-control problem.

Why the other options are incorrect:

Option A is incorrect because a domestic-water aerator does not control thermal expansion in the closed collector loop.
Option C is incorrect because collector heating contributes to fluid expansion, but glazing does not eliminate the need for a properly functioning expansion tank.
Option D is incorrect because the domestic hot-water thermostat does not replace the collector loop’s required pressure and expansion controls.

Quick Study Guide:

Solar thermal fluid expands as its temperature rises.
The expansion tank accommodates volume changes and helps control pressure.
Check tank sizing, diaphragm condition, precharge, and manufacturer specifications.
Never disable a pressure-relief valve to stop fluid discharge.

Question 5. During installation of a new refrigeration system, a technician must pressure-test the refrigerant piping before evacuation and charging. The manufacturer specifies a test pressure that is within the allowable rating of the installed components. Which procedure is the safest and most appropriate?

A. Use oxygen at the specified pressure because it is readily available and does not leave moisture in the piping.
B. Use compressed shop air and increase the pressure above the manufacturer’s limit to expose small leaks more quickly.
C. Use dry nitrogen with a suitable pressure regulator and approved test equipment, increase pressure in controlled stages, and never exceed the applicable component or manufacturer limits.
D. Introduce refrigerant vapor into the piping and ignite it briefly to identify leaking joints.

Correct Answer: C. Use dry nitrogen with a suitable pressure regulator and approved test equipment, increase pressure in controlled stages, and never exceed the applicable component or manufacturer limits.

Answer Explanation:
Option C is correct because dry nitrogen is commonly used to pressure-test refrigeration piping when permitted by the manufacturer’s procedures. It is nonflammable and helps avoid introducing moisture or oxygen into the system. A suitable regulator, pressure-rated hoses, appropriate gauges, and compatible leak-detection equipment are essential. The technician should raise pressure in controlled stages, inspect joints and connections, and remain within the specified test pressure for every component. Oxygen and ordinary compressed air must never be substituted for an approved inert test gas because they can create dangerous reactions with refrigeration oils and other materials under pressure. After successful testing, the system must be properly evacuated before charging in accordance with the manufacturer’s requirements.

Why the other options are incorrect:

Option A is incorrect because oxygen can react violently with oil and other combustible materials under pressure.
Option B is incorrect because shop air can introduce moisture and oxygen, while exceeding pressure limits can damage components or cause injury.
Option D is incorrect because ignition is an unacceptable leak-testing method and creates a serious fire and explosion hazard.

Quick Study Guide:

Use dry nitrogen for pressure testing when the manufacturer specifies it.
Never use oxygen or ordinary compressed air to pressure-test refrigeration circuits.
Use a regulator and never exceed the lowest applicable component pressure limit.
Pressure testing and evacuation are separate procedures; evacuate before charging.