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Missouri St. Louis County Commercial HVAC
Servicer-Installer 588-MO-SL Contractor EXAM
LATEST VERSION 2026-2027 QUESTIONS WITH
CORRECT SOLUTIONS ALL WITH DETAILED
RATIONALES JUST RELEASED THIS YEAR
EXAM COVERAGE SUMMARY
The 588-MO-SL Commercial HVAC Servicer/Installer exam assesses your competency across
several critical domains:
• Local Licensing Law (≈5%): St. Louis County's specific requirements for mechanical
contractor licensing, continuing education, and permit procedures.
• Local Mechanical Amendments (≈10%): St. Louis County's specific modifications and
additions to the International Mechanical Code (IMC).
• Applied Math (≈6%): Mathematical principles applied to HVAC design, load calculations,
and system sizing.
• Air Distribution (≈15%): Design and installation of air distribution systems, including
ductwork materials, airflow principles, and balancing techniques.
• Gas Furnaces and Piping (≈15%): Installation, maintenance, and safety protocols for gas
furnaces and gas piping systems.
• Piping in HVAC Systems (≈12%): Installation and maintenance of various piping systems
used in commercial heating and cooling applications.
• Refrigeration & Electrical (≈12%): Principles of thermodynamics, electrical components,
and troubleshooting.
• Safety & EPA Regulations (≈10%): OSHA safety standards, EPA Section 608 refrigerant
management, and other key safety practices.
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• Professional & Business Practices (≈15%): Permit applications, inspections, liability
insurance, and record-keeping.
250 Random Practice Questions
Question 1: A commercial client asks you to install a used condensing unit from an old project
into a new building addition. What is the most appropriate action?
A) Install the unit as requested, as it's perfectly functional.
B) Explain that used equipment is only allowed in existing systems, not new builds, without
specific county approval.
C) Proceed with the installation but keep it off the official permit record.
D) Dispose of the unit and install a new one without telling the client.
Answer: B
Installing used HVAC equipment in a new commercial build is generally prohibited in St. Louis
County; such equipment may only be installed in existing systems with prior county inspection
approval.
Question 2: While performing a duct leakage test, what is the maximum acceptable leakage
percentage for a commercial system operating at 25% of its design pressure?
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A) 1%
B) 2%
C) 5%
D) 10%
Answer: B
The Missouri mechanical code, as enforced locally, requires a duct leakage test at 25% of design
pressure, and the leakage rate must not exceed 2% to ensure system efficiency and integrity.
Question 3: What is the specific slope requirement for a horizontal drain line connected to an
evaporator coil in a commercial HVAC system?
A) 1/8 inch per foot
B) 1/4 inch per foot
C) 1/2 inch per foot
D) 1 inch per foot
Answer: B
To ensure proper condensate removal and prevent overflow or microbial growth, horizontal
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drain lines must be sloped at a minimum of one-quarter inch per foot towards the drain
termination point.
Question 4: A registered HVAC contractor in St. Louis County must renew their license by which
specific date each year?
A) June 30th
B) September 30th
C) December 31st
D) The anniversary of the license issue date
Answer: C
The St. Louis County licensing ordinance mandates that all mechanical contractor licenses are
renewed annually and must be renewed by December 31st of each year to remain valid.
Question 5: What is the maximum length allowed for a flexible duct connector in a commercial
HVAC system as per Missouri mechanical code?
A) 7 inches
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SUCCESS!
Missouri St. Louis County Commercial HVAC
Servicer-Installer 588-MO-SL Contractor EXAM
LATEST VERSION 2026-2027 QUESTIONS WITH
CORRECT SOLUTIONS ALL WITH DETAILED
RATIONALES JUST RELEASED THIS YEAR
EXAM COVERAGE SUMMARY
The 588-MO-SL Commercial HVAC Servicer/Installer exam assesses your competency across
several critical domains:
• Local Licensing Law (≈5%): St. Louis County's specific requirements for mechanical
contractor licensing, continuing education, and permit procedures.
• Local Mechanical Amendments (≈10%): St. Louis County's specific modifications and
additions to the International Mechanical Code (IMC).
• Applied Math (≈6%): Mathematical principles applied to HVAC design, load calculations,
and system sizing.
• Air Distribution (≈15%): Design and installation of air distribution systems, including
ductwork materials, airflow principles, and balancing techniques.
• Gas Furnaces and Piping (≈15%): Installation, maintenance, and safety protocols for gas
furnaces and gas piping systems.
• Piping in HVAC Systems (≈12%): Installation and maintenance of various piping systems
used in commercial heating and cooling applications.
• Refrigeration & Electrical (≈12%): Principles of thermodynamics, electrical components,
and troubleshooting.
• Safety & EPA Regulations (≈10%): OSHA safety standards, EPA Section 608 refrigerant
management, and other key safety practices.
1
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• Professional & Business Practices (≈15%): Permit applications, inspections, liability
insurance, and record-keeping.
250 Random Practice Questions
Question 1: A commercial client asks you to install a used condensing unit from an old project
into a new building addition. What is the most appropriate action?
A) Install the unit as requested, as it's perfectly functional.
B) Explain that used equipment is only allowed in existing systems, not new builds, without
specific county approval.
C) Proceed with the installation but keep it off the official permit record.
D) Dispose of the unit and install a new one without telling the client.
Answer: B
Installing used HVAC equipment in a new commercial build is generally prohibited in St. Louis
County; such equipment may only be installed in existing systems with prior county inspection
approval.
Question 2: While performing a duct leakage test, what is the maximum acceptable leakage
percentage for a commercial system operating at 25% of its design pressure?
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A) 1%
B) 2%
C) 5%
D) 10%
Answer: B
The Missouri mechanical code, as enforced locally, requires a duct leakage test at 25% of design
pressure, and the leakage rate must not exceed 2% to ensure system efficiency and integrity.
Question 3: What is the specific slope requirement for a horizontal drain line connected to an
evaporator coil in a commercial HVAC system?
A) 1/8 inch per foot
B) 1/4 inch per foot
C) 1/2 inch per foot
D) 1 inch per foot
Answer: B
To ensure proper condensate removal and prevent overflow or microbial growth, horizontal
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drain lines must be sloped at a minimum of one-quarter inch per foot towards the drain
termination point.
Question 4: A registered HVAC contractor in St. Louis County must renew their license by which
specific date each year?
A) June 30th
B) September 30th
C) December 31st
D) The anniversary of the license issue date
Answer: C
The St. Louis County licensing ordinance mandates that all mechanical contractor licenses are
renewed annually and must be renewed by December 31st of each year to remain valid.
Question 5: What is the maximum length allowed for a flexible duct connector in a commercial
HVAC system as per Missouri mechanical code?
A) 7 inches
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