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The MD-MHVACR exam has 100 questions and runs 4 hours.
These 10 free MD-MHVACR questions are organized by exam domain, so you can see how each part of the Maryland Master HVACR Contractor License Exam blueprint is tested. Reveal the answer and explanation under each question.
An electric-heat contactor will not energize even though the thermostat is calling. The transformer measures 24 VAC from R to C. With the control circuit energized, the meter reads 24 VAC across the high-limit switch and about 0 VAC across each of the other series safeties. What does this establish?
Correct answer: A - The high-limit contacts are open
Three unmarked terminals on a single-phase hermetic compressor are X, Y, and Z. Resistance readings are X-Y = 0.8 ohm, X-Z = 2.4 ohms, and Y-Z = 3.2 ohms; no terminal has continuity to the shell. Which identification is correct?
Correct answer: B - X = common, Y = run, Z = start
Black copper-oxide scale is found inside newly installed ACR tubing downstream of several field-brazed joints. During replacement of the contaminated piping, which work practice best prevents the same internal scale?
Correct answer: A - Flow low-pressure dry nitrogen through the tubing while brazing
On a previously commissioned TXV-equipped split system, design airflow, coil cleanliness, and load have been verified. Suction and head pressures are both below the manufacturer's expected range, superheat is 22°F, and subcooling is 4°F. Which condition best fits the complete pattern?
Correct answer: C - Refrigerant undercharge caused by leakage
The condensate pan of a draw-through air handler fills while the blower runs, but drains rapidly as soon as the blower stops. The drain connection is on the negative-pressure side of the fan, the piping has continuous fall, and no trap is installed. What modification addresses the operating cause?
Correct answer: C - Install and prime a correctly dimensioned condensate trap
A fixed-orifice cooling system has low suction pressure, a frosted evaporator, and a 30°F return-to-supply dry-bulb split. The return filter is heavily loaded, the blower wheel is dirty, and measured airflow is well below the equipment range. What should be done before any refrigerant adjustment?
Correct answer: C - Restore airflow, thaw the coil, and repeat the complete operating measurements
While checking an atmospheric gas furnace, a contractor measures carbon monoxide in the occupied area, observes continuous spillage at the draft hood, and learns that two occupants have headaches. What is the immediate priority?
Correct answer: D - Shut the appliance down, move occupants to fresh air, ventilate safely, and activate emergency response
At steady operation, a furnace has 100,000 Btu/h input, 80% thermal efficiency, and 1,000 CFM measured airflow. Its nameplate temperature-rise range is 35°F to 65°F. Which conclusion follows from these readings?
Correct answer: D - The expected rise is about 74°F; verify input and correct inadequate airflow before return to service
During final air balance, every supply terminal measures 20% to 30% below design. Filters and coils are clean, all volume dampers are open, fan rotation is correct, the blower is already at its approved maximum speed, and measured external static pressure exceeds the unit's rating. Which corrective direction is justified?
Correct answer: B - Locate and reduce the excessive system resistance or undersized critical path
For the critical duct path, a blower can provide 0.80 in. w.g. external static pressure at design airflow. The filter, coil, and terminal devices consume 0.60 in. w.g., and total effective length is 200 ft. Which friction-rate setting should be used for duct sizing?
Correct answer: D - 0.10 in. w.g. per 100 ft
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