- Exam Overview and Format
- Domain 1: Electrical Knowledge, Motors, and Controls
- Domain 2: Piping
- Domain 3: Refrigeration and Air Conditioning
- Domain 4: Heating Systems
- Domain 5: Air Distribution Systems
- Domain 6: Safety
- Domain Weighting and How to Schedule Your Prep
- What You Can Bring Into the Exam Room
- Registration, Fees, and Retesting
- Frequently Asked Questions
- The MD-MHVACR exam covers six domains: Electrical, Piping, Refrigeration and Air Conditioning, Heating Systems, Air Distribution, and Safety.
- Refrigeration and Air Conditioning is the largest domain, so it deserves the most study hours.
- The exam is 100 questions, open-book, with a 4-hour limit and a 70% passing score.
- Approved references include the IMC, Modern Refrigeration and Air Conditioning, Manual J, OSHA 29 CFR 1926, and an ACCA Ductulator.
Exam Overview and Format
The Maryland Board of Heating, Ventilation, Air Conditioning and Refrigeration Contractors administers the Master HVACR Contractor examination through PSI, and every question on that exam is pulled from six defined content areas. Before diving into domain specifics, it helps to understand the container these domains live inside: a computer-delivered, open-book, multiple-choice test with 100 questions, a 4-hour time limit, and a 70% passing score. The exam fee is $150.
Because the test is open-book, the domains aren't just about memorization - they're about knowing exactly where to find code language, sizing tables, and refrigeration data fast enough to finish 100 questions in four hours. If you haven't already reviewed the eligibility requirements, take a look at our breakdown of MD-MHVACR requirements before you commit study time to domain content, since you'll need at least three years of licensed, regularly employed experience as a Journeyman, Limited Contractor, Master Restricted Contractor, or HVACR instructor, working under a licensed Master Contractor, plus documentation of at least 1,875 hours of HVACR services in the year before you apply.
Domain 1: Electrical Knowledge, Motors, and Controls
This domain tests your ability to read wiring diagrams, diagnose motor and control circuit problems, and understand the electrical components that keep HVACR equipment running. Expect scenario-based questions where you're given symptoms (a compressor that hums but won't start, a fan motor that cycles on overload) and asked to identify the likely cause.
Electrical Knowledge, Motors, and Controls
Candidates must be comfortable with both single-phase and three-phase systems, and with the control components that tie a system's electrical side to its mechanical side.
- Run and start capacitors, relays, and contactors
- Single-phase vs. three-phase motor characteristics and starting methods
- Transformers, control voltage circuits, and low-voltage wiring diagrams
- Using a multimeter to troubleshoot open circuits, shorts, and grounds
- Overload protection and motor safety devices
Because this domain blends theory with troubleshooting logic, it rewards candidates who have hands-on field experience diagnosing electrical faults rather than those who only memorized definitions.
Domain 2: Piping
Piping questions cover both refrigerant piping and the broader mechanical piping practices a Master Contractor is responsible for overseeing on a job site. You'll need working knowledge of pipe sizing, joining methods, and code-driven installation practices.
Piping
This domain checks whether you can size, route, and properly join piping systems while keeping oil return and code compliance in mind.
- Refrigerant line sizing for suction, liquid, and hot gas lines
- Brazing and soldering procedures for copper piping
- Condensate piping, traps, and drainage requirements
- Gas piping sizing referenced from the International Mechanical Code
- Proper support, insulation, and vibration isolation practices
Piping questions often overlap with the Refrigeration and Air Conditioning domain, so studying oil return and line sizing here reinforces material you'll need again later.
Domain 3: Refrigeration and Air Conditioning
Refrigeration and Air Conditioning is the largest domain on the exam, which means it deserves the largest share of your prep time. This domain covers the refrigeration cycle from end to end: compression, condensation, metering, and evaporation, along with the diagnostic math that separates a Journeyman from a Master.
Refrigeration and Air Conditioning (Largest Domain)
Candidates are expected to understand system diagnostics at a Master level, not just component identification.
- Superheat and subcooling calculations for TXV and fixed-orifice systems
- Compressor types: reciprocating, scroll, and screw compressors
- Metering device operation and troubleshooting
- Refrigerant recovery, recycling, and reclaim procedures
- Evaporator and condenser sizing and airflow-to-charge relationships
Key Takeaway
Since Refrigeration and Air Conditioning is the largest domain, allocate more practice questions and review sessions to superheat/subcooling math and metering device troubleshooting than to any other single topic.
Modern Refrigeration and Air Conditioning (editions 19 through 21) is one of the approved references for this section, so becoming familiar with how that text organizes refrigeration cycle diagrams will save you time during the actual exam.
Domain 4: Heating Systems
This domain covers combustion-based and electric heating equipment, including furnaces, boilers, and heat pumps in heating mode. Expect questions on ignition sequences, venting categories, and combustion safety.
Heating Systems
You'll need to know how different heating appliances ignite, combust, and vent safely, plus how heat pumps behave differently from combustion equipment.
- Gas and oil furnace ignition sequences and safety controls
- Boiler operation, staging, and safety devices
- Heat pump operation in heating mode, including defrost cycles
- Venting categories and combustion air requirements from the IMC
- Combustion troubleshooting and efficiency considerations
Because this exam is open-book, you don't need to memorize every IMC table cold - but you do need to know which chapter covers venting so you're not flipping through the entire code book mid-exam.
Domain 5: Air Distribution Systems
Air Distribution Systems questions test duct design, airflow, and load calculation skills. This is where your ACCA Ductulator becomes essential, since you're permitted to bring one into the testing room.
Air Distribution Systems
This domain focuses on moving conditioned air efficiently and correctly through a structure.
- Duct sizing using an ACCA Ductulator
- Static pressure calculations and troubleshooting high or low readings
- Manual J load calculation fundamentals (referenced from the 2006 eighth edition)
- Supply and return duct design principles
- Air balancing and distribution accessories
Practice pulling numbers off a Ductulator before exam day. Fumbling with an unfamiliar tool under a four-hour time limit costs more minutes than most candidates expect.
Domain 6: Safety
The Safety domain draws heavily from OSHA 29 CFR Part 1926, one of the approved references for the exam. Expect questions on jobsite hazard recognition, fall protection, and safe handling of refrigerants and equipment.
Safety
Safety questions test your knowledge of regulatory standards and your judgment in real jobsite scenarios.
- OSHA 29 CFR 1926 general industry and construction safety provisions
- Ladder safety and fall protection requirements
- Lockout/tagout procedures for electrical and mechanical equipment
- Safe refrigerant handling and recovery practices
- Personal protective equipment requirements for HVACR technicians
Domain Weighting and How to Schedule Your Prep
Since Refrigeration and Air Conditioning is confirmed as the largest domain, it should anchor your study calendar. The table below reflects the six domains you'll encounter - use it to plan review order rather than to guess at percentages the Board hasn't published.
| Domain | Core Focus | Key Approved Reference |
|---|---|---|
| Electrical Knowledge, Motors, and Controls | Wiring diagrams, motor troubleshooting, control circuits | Modern Refrigeration and Air Conditioning |
| Piping | Refrigerant and mechanical piping, sizing, joining | International Mechanical Code |
| Refrigeration and Air Conditioning | Refrigeration cycle diagnostics, superheat/subcooling | Modern Refrigeration and Air Conditioning |
| Heating Systems | Furnaces, boilers, heat pumps, venting | International Mechanical Code |
| Air Distribution Systems | Duct sizing, static pressure, load calculations | Manual J, ACCA Ductulator |
| Safety | Jobsite hazards, OSHA compliance, refrigerant handling | OSHA 29 CFR Part 1926 |
Refrigeration and Air Conditioning
- Drill superheat and subcooling calculations daily
- Review compressor types and metering device diagnostics
- Study refrigerant recovery and reclaim procedures
Piping and Electrical
- Practice refrigerant line sizing and brazing procedures
- Review motor starting methods and control circuit diagrams
Heating and Air Distribution
- Study combustion, venting, and ignition sequences
- Practice Ductulator sizing and static pressure problems
Safety and Full Review
- Review OSHA 29 CFR 1926 hazard categories
- Take timed practice sets across all six domains
For a more detailed week-by-week breakdown with practice question strategies, see our full MD-MHVACR study guide.
What You Can Bring Into the Exam Room
Because this is an open-book exam, knowing your references cold matters almost as much as knowing the domain content itself. Approved references include the 2012 or 2018 International Mechanical Code, Modern Refrigeration and Air Conditioning (editions 19 through 21), Manual J 2006 eighth edition, OSHA 29 CFR Part 1926, and an ACCA Ductulator.
If you're still deciding how confident you feel about the material, our guide on how hard the MD-MHVACR exam really is breaks down what makes this test challenging even with open-book access, and our passing score guide explains exactly what a 70% cutoff means for how many questions you can afford to miss.
Registration, Fees, and Retesting
Once you've mapped your study plan to the six domains, the logistics are straightforward. The exam fee is $150, paid when you schedule through PSI. If you don't pass on your first attempt, you'll need to wait 30 days before requesting a retest; any subsequent retest request requires a 60-day wait.
Passing the exam is only part of becoming a Master Contractor. The current Master license fee is $94.50, and Master Contractors subject to the insurance requirement must maintain $300,000 in general-liability insurance and $100,000 in property-damage insurance. Maryland also offers HVACR reciprocity with Delaware and Virginia, which can matter if you plan to work across state lines.
Keep a printable reference of these numbers alongside the domain breakdown above - our MD-MHVACR cheat sheet condenses all of this into a one-page review for last-minute checks before you head into the testing center.
Want to test your domain knowledge before exam day? Head over to our practice test platform and work through domain-specific question sets that mirror the real exam's open-book, scenario-driven style. Running through timed practice exams is one of the most reliable ways to confirm you can finish all 100 questions inside the 4-hour limit.
Frequently Asked Questions
Start with Refrigeration and Air Conditioning since it's the largest domain on the exam. Building strong superheat, subcooling, and metering device knowledge early also reinforces material you'll see again in the Piping domain.
Yes. The entire 100-question exam is open-book, and the same approved references - including the IMC, Modern Refrigeration and Air Conditioning, Manual J, OSHA 29 CFR 1926, and an ACCA Ductulator - apply across all six domains.
Your ACCA Ductulator is primarily useful for Air Distribution Systems questions, but duct sizing concepts can appear in scenario questions tied to overall system design, so it's worth keeping it handy throughout the exam.
The Board has not published an exact question count per domain, only that Refrigeration and Air Conditioning is the largest. Plan your 100-question review time proportionally, with the heaviest emphasis on that domain.
You'll need to wait 30 days before requesting your first retest. If you fail again, any later retest request requires a 60-day wait, so thorough domain-by-domain preparation before your first attempt is worth the extra time upfront.