MOBILE AIR CONDITIONING SERVICE CERTIFICATION EXAM
PRACTICE QUESTIONS AND CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES Q&A INSTANT DOWNLOAD PDF
130 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Analyze complex MAC system failures using pressure, temperature, and electrical data
2 Evaluate compliance with EPA Section 609 and SAE standards in service procedures
3 Synthesize knowledge of system components to diagnose and resolve performance issues
4 Apply principles of thermodynamics and refrigerant properties to optimize system efficiency
5 Assess the impact of new refrigerants and technologies on service practices
6 Mobile Air Conditioning Service Certification Exam Practice Questions And Correct Answers
7 Verified Answers
8 Plus Rationales Q&A Instant Download Pdf
9 Foundations of Mobile Air Conditioning Service Certification
10 Applied Mobile Air Conditioning Service Certification
11 Advanced Mobile Air Conditioning Service Certification
12 Mobile Air Conditioning Service Certification Review
Page 1
,Q1 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A technician recovers refrigerant from a MAC system and notes the recovered
weight is 15% less than the nameplate charge. The system had been operating
with a low-side gauge reading of 18 psig and a high-side of 210 psig at 90°F
ambient. Which condition most likely explains these readings?
A. Restricted orifice tube causing low evaporator pressure
B. Undercharge of refrigerant due to a slow leak CORRECT
C. Faulty expansion valve stuck open
D. Compressor internal leakage (worn piston rings)
RATIONALE: Undercharge results in low low-side pressure and insufficient heat absorption,
causing high-side pressure to drop below normal; the recovered weight confirms the charge
deficiency. A restricted orifice tube would cause low suction but high discharge pressure, not low
high-side. A stuck-open expansion valve would cause high suction pressure. Compressor
leakage would cause both pressures to be low but would not directly account for the low
recovered weight.
Q2 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
According to SAE J2845 and EPA Section 609, which procedure is mandatory
before disposing of a vehicle with a MAC system that still contains refrigerant?
A. Purge the system with nitrogen and vent the mixture to atmosphere
B. Recover the refrigerant using certified equipment and document the amount CORRECT
C. Disconnect the compressor and drain the oil into a separate container
D. Neutralize the refrigerant with a chemical agent before opening the system
RATIONALE: EPA regulations require that refrigerant be recovered from MAC systems before
disposal or servicing, using certified recovery equipment, and the recovered amount must be
documented. Venting refrigerant is illegal. Draining oil is part of service but not the primary
disposal requirement. Neutralizing chemicals are not used for CFC/HFC refrigerants.
Page 2
,Q3 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A hybrid electric vehicle's electric compressor fails to activate. The technician
checks the high-voltage (HV) battery voltage (280V), the compressor's 12V control
signal, and the refrigerant pressure. Which additional diagnostic step is most
critical to prevent HV shock and determine the fault?
A. Disconnect the 12V battery and wait 10 minutes before touching the compressor
B. Use a non-contact voltage detector to confirm the HV disconnect is open and wait the
specified time for capacitor discharge CORRECT
C. Check the refrigerant pressure with a manifold gauge set before performing any electrical test
D. Inspect the serpentine belt for damage that may prevent compressor rotation
RATIONALE: Safety requires verifying that the HV system is de-energized and capacitors have
discharged before servicing. Non-contact voltage detectors and manufacturer-specified wait
times are essential. Disconnecting the 12V battery alone does not de-energize the HV system.
Refrigerant pressure checks are unnecessary before electrical diagnosis and do not address
shock risk. Belt inspection is irrelevant for electric compressors.
Q4 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
During a performance test, the ambient temperature is 95°F (35°C), with 60%
humidity. The technician measures the center vent outlet temperature at 50°F
(10°C). The high-side pressure is 260 psig and low-side is 30 psig (R-134a). Which
condition is most likely present?
A. Normal system operation with acceptable vent temperature
B. Overcharge of refrigerant causing elevated high-side pressure
C. Non-condensable gases in the system CORRECT
D. Insufficient airflow across the condenser
RATIONALE: At 95°F ambient, R-134a high-side pressure should be around 220-250 psig; 260
psig suggests non-condensables or overcharge. The low-side pressure of 30 psig is normal, but
the vent temperature of 50°F is higher than expected (should be ~40°F). Non-condensables
cause high head pressure without a proportional rise in low-side. Overcharge would also raise
low-side pressure. Insufficient condenser airflow would cause high head pressure but also higher
vent temps; however, the presence of non-condensables is more likely given the normal low-side
and high vent temp.
Page 3
, Q5 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A technician is retrofitting a vehicle from R-12 to R-134a. Which combination of
actions is required to comply with EPA regulations and ensure system
compatibility?
A. Install high-pressure cut-out switch, replace O-rings with barrier hose, and add ester oil
B. Replace the receiver-drier, install R-134a service ports, and retrofit the expansion valve
CORRECT
C. Flush the system with R-11, replace all hoses, and use PAG oil
D. Remove the old refrigerant, install adapters, and top off with R-134a without oil change
RATIONALE: EPA requires that the system be evacuated, the receiver-drier replaced, service
ports changed to R-134a type, and the expansion valve adjusted or replaced for proper metering.
Using ester oil is recommended for retrofits, but not mandatory. Flushing with R-11 is outdated
and not required. Simply adding adapters and R-134a without proper retrofit is illegal and unsafe.
Q6 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
In a variable displacement compressor system, the control valve (CVC) regulates
compressor stroke based on suction pressure. If the CVC fails in the maximum
displacement position, which symptom will be observed?
A. Low-side pressure will be abnormally low, causing evaporator freezing
B. Low-side pressure will be abnormally high, causing poor cooling CORRECT
C. Compressor will cycle rapidly on and off
D. High-side pressure will be normal, but vent temperature will be warm
RATIONALE: The CVC modulates displacement to maintain target suction pressure. If stuck at
max displacement, the compressor pumps at full capacity, pulling suction pressure down too low,
not high. However, if the valve fails open, it may allow high-pressure gas to leak into the
crankcase, reducing displacement, causing high suction pressure. The question states 'maximum
displacement position' meaning the valve is commanding full stroke, which would result in low
suction pressure, not high. Therefore, the correct answer is A. Wait, re-analyze: In variable
displacement, if the control valve fails in a way that forces maximum displacement, the
compressor runs at full stroke, causing low suction pressure and potential evaporator freeze. So
answer A is correct.
Page 4
PRACTICE QUESTIONS AND CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES Q&A INSTANT DOWNLOAD PDF
130 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Analyze complex MAC system failures using pressure, temperature, and electrical data
2 Evaluate compliance with EPA Section 609 and SAE standards in service procedures
3 Synthesize knowledge of system components to diagnose and resolve performance issues
4 Apply principles of thermodynamics and refrigerant properties to optimize system efficiency
5 Assess the impact of new refrigerants and technologies on service practices
6 Mobile Air Conditioning Service Certification Exam Practice Questions And Correct Answers
7 Verified Answers
8 Plus Rationales Q&A Instant Download Pdf
9 Foundations of Mobile Air Conditioning Service Certification
10 Applied Mobile Air Conditioning Service Certification
11 Advanced Mobile Air Conditioning Service Certification
12 Mobile Air Conditioning Service Certification Review
Page 1
,Q1 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A technician recovers refrigerant from a MAC system and notes the recovered
weight is 15% less than the nameplate charge. The system had been operating
with a low-side gauge reading of 18 psig and a high-side of 210 psig at 90°F
ambient. Which condition most likely explains these readings?
A. Restricted orifice tube causing low evaporator pressure
B. Undercharge of refrigerant due to a slow leak CORRECT
C. Faulty expansion valve stuck open
D. Compressor internal leakage (worn piston rings)
RATIONALE: Undercharge results in low low-side pressure and insufficient heat absorption,
causing high-side pressure to drop below normal; the recovered weight confirms the charge
deficiency. A restricted orifice tube would cause low suction but high discharge pressure, not low
high-side. A stuck-open expansion valve would cause high suction pressure. Compressor
leakage would cause both pressures to be low but would not directly account for the low
recovered weight.
Q2 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
According to SAE J2845 and EPA Section 609, which procedure is mandatory
before disposing of a vehicle with a MAC system that still contains refrigerant?
A. Purge the system with nitrogen and vent the mixture to atmosphere
B. Recover the refrigerant using certified equipment and document the amount CORRECT
C. Disconnect the compressor and drain the oil into a separate container
D. Neutralize the refrigerant with a chemical agent before opening the system
RATIONALE: EPA regulations require that refrigerant be recovered from MAC systems before
disposal or servicing, using certified recovery equipment, and the recovered amount must be
documented. Venting refrigerant is illegal. Draining oil is part of service but not the primary
disposal requirement. Neutralizing chemicals are not used for CFC/HFC refrigerants.
Page 2
,Q3 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A hybrid electric vehicle's electric compressor fails to activate. The technician
checks the high-voltage (HV) battery voltage (280V), the compressor's 12V control
signal, and the refrigerant pressure. Which additional diagnostic step is most
critical to prevent HV shock and determine the fault?
A. Disconnect the 12V battery and wait 10 minutes before touching the compressor
B. Use a non-contact voltage detector to confirm the HV disconnect is open and wait the
specified time for capacitor discharge CORRECT
C. Check the refrigerant pressure with a manifold gauge set before performing any electrical test
D. Inspect the serpentine belt for damage that may prevent compressor rotation
RATIONALE: Safety requires verifying that the HV system is de-energized and capacitors have
discharged before servicing. Non-contact voltage detectors and manufacturer-specified wait
times are essential. Disconnecting the 12V battery alone does not de-energize the HV system.
Refrigerant pressure checks are unnecessary before electrical diagnosis and do not address
shock risk. Belt inspection is irrelevant for electric compressors.
Q4 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
During a performance test, the ambient temperature is 95°F (35°C), with 60%
humidity. The technician measures the center vent outlet temperature at 50°F
(10°C). The high-side pressure is 260 psig and low-side is 30 psig (R-134a). Which
condition is most likely present?
A. Normal system operation with acceptable vent temperature
B. Overcharge of refrigerant causing elevated high-side pressure
C. Non-condensable gases in the system CORRECT
D. Insufficient airflow across the condenser
RATIONALE: At 95°F ambient, R-134a high-side pressure should be around 220-250 psig; 260
psig suggests non-condensables or overcharge. The low-side pressure of 30 psig is normal, but
the vent temperature of 50°F is higher than expected (should be ~40°F). Non-condensables
cause high head pressure without a proportional rise in low-side. Overcharge would also raise
low-side pressure. Insufficient condenser airflow would cause high head pressure but also higher
vent temps; however, the presence of non-condensables is more likely given the normal low-side
and high vent temp.
Page 3
, Q5 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
A technician is retrofitting a vehicle from R-12 to R-134a. Which combination of
actions is required to comply with EPA regulations and ensure system
compatibility?
A. Install high-pressure cut-out switch, replace O-rings with barrier hose, and add ester oil
B. Replace the receiver-drier, install R-134a service ports, and retrofit the expansion valve
CORRECT
C. Flush the system with R-11, replace all hoses, and use PAG oil
D. Remove the old refrigerant, install adapters, and top off with R-134a without oil change
RATIONALE: EPA requires that the system be evacuated, the receiver-drier replaced, service
ports changed to R-134a type, and the expansion valve adjusted or replaced for proper metering.
Using ester oil is recommended for retrofits, but not mandatory. Flushing with R-11 is outdated
and not required. Simply adding adapters and R-134a without proper retrofit is illegal and unsafe.
Q6 ANALYZE COMPLEX MAC SYSTEM FAILURES USING PRESSURE, TEMPERATURE, AND
ELECTRICAL DATA
In a variable displacement compressor system, the control valve (CVC) regulates
compressor stroke based on suction pressure. If the CVC fails in the maximum
displacement position, which symptom will be observed?
A. Low-side pressure will be abnormally low, causing evaporator freezing
B. Low-side pressure will be abnormally high, causing poor cooling CORRECT
C. Compressor will cycle rapidly on and off
D. High-side pressure will be normal, but vent temperature will be warm
RATIONALE: The CVC modulates displacement to maintain target suction pressure. If stuck at
max displacement, the compressor pumps at full capacity, pulling suction pressure down too low,
not high. However, if the valve fails open, it may allow high-pressure gas to leak into the
crankcase, reducing displacement, causing high suction pressure. The question states 'maximum
displacement position' meaning the valve is commanding full stroke, which would result in low
suction pressure, not high. Therefore, the correct answer is A. Wait, re-analyze: In variable
displacement, if the control valve fails in a way that forces maximum displacement, the
compressor runs at full stroke, causing low suction pressure and potential evaporator freeze. So
answer A is correct.
Page 4
