Delaware HVAC Exam Prep FREE Sample Exam — Fixed Set

An evaporator has heavy frost building on the coil, low suction pressure, a warm conditioned space, and weak airflow from the registers. Inspection finds a very dirty air filter restricting air through the coil. The cause is most likely:

An overcharge of refrigerant

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A condenser fan running backwards

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Low airflow across the evaporator, which drops coil temperature below freezing and builds frost that blocks airflow further

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A liquid-line restriction after the filter drier that starves the evaporator, raises superheat, and reduces cooling in the last circuits of the coil downstream

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A homeowner asks why the new R-454B air handler runs its blower for a while after a leak sensor trips, even though cooling has stopped. What is the correct explanation?

The blower is removing residual heat from the electric heat strips, a normal cool-down sequence that happens to coincide with the sensor alarm event

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The blower pressurizes the duct system so refrigerant vapor is forced back through the leak point into the coil, resealing the system temporarily

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The blower dilutes and disperses leaked refrigerant through the duct system so room concentration stays low

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The blower run is a fault in itself, because mitigation design requires the air handler to shut down every moving part the instant a sensor trips

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Where is a fuel deaerator typically installed, and what must its vent or return arrangement do?

Inside the oil tank itself, submerged in fuel, where it vents air bubbles directly into the stored oil for reabsorption later

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On the burner fuel unit discharge, where it stores high-pressure oil to smooth nozzle pressure pulses during ignition trials

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In the flue pipe, where exhaust heat boils air out of the oil before the oil returns through the chimney to the tank top

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Near the burner, venting separated air safely

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A technician sets the closed-position stop on non-calling zone dampers so each blade leaks a small amount of air instead of sealing fully. What is the purpose, and the cost?

The leak prevents damper blades from sticking after long idle periods, and its cost is the motor wear caused by the panel driving the blades against the stop repeatedly

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The bleed relieves some excess pressure, at the cost of conditioning zones that are not calling

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The leak equalizes humidity between zones, and its cost is that satisfied zones slowly take on the moisture load of calling zones through the shared return system

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The bleed raises total airflow so the smallest zone can be served without a bypass, and its cost is that the equipment must be oversized for the whole house to feed the leakage

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A 24 V contactor coil measures 15 ohms. Using Ohm’s law, about how much current does the coil draw when energized?

0.63 A

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1.6 A

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39 A

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360 A

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A long liquid line is one size too small for the load. The most likely operating symptom is:

No symptom, because liquid lines cannot have pressure drop no matter how small the tubing, how long the run, or how many elbows, valves, and vertical lifts are installed between the receiver and the expansion device

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Oil logging in the liquid line riser

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Excessive pressure drop that consumes subcooling and can flash liquid to vapor before the expansion valve, reducing its capacity

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A suction line that sweats heavily indoors

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Where does a fan-powered humidifier belong, and why does placement matter?

In the return drop only, because fan-powered models depend entirely on the return airstream being warmer than the supply airstream

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Loose in the blower compartment, where unducted air movement across the panel provides enough evaporation for a whole house

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On the outdoor condensing unit, where weather provides airflow and the moisture can be piped indoors with the refrigerant lines

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On the supply plenum, where its own fan pushes air through the water panel independent of bypass duct pressure differences.

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In January a house shows heavy window condensation and RH of 55% indoors at 70°F, with no plumbing or roof leaks found. What is the most likely explanation?

Outdoor winter air leaking in is humidifying the house, because cold outdoor air holds more moisture than warm indoor air and releases it at the windows

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The windows are defective and are generating moisture at the glass, which is why condensation appears there first instead of anywhere else in the rooms

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The furnace humidifier has failed empty and is somehow adding moisture, since window condensation in winter is a standard symptom of too little indoor humidity

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Indoor vapor condensing on cold glass

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The same model of air conditioner is being selected for two identical houses, one near sea level and one at about 6,000 feet elevation. Why can’t the designer simply use the same airflow and capacity assumptions for both?

At elevation the air is less dense, so each cubic foot carries less heat: the system needs more CFM to move the same heat, and rated capacities and combustion appliance inputs must be corrected for the thinner air

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At elevation air is denser, so airflow should be reduced by the same percentage, because each cubic foot delivered at altitude carries more heat than it would at sea level and the coil therefore needs less volume moving across it in both heating and cooling operation

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Elevation affects only heating equipment, never cooling airflow

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Standard sea-level tables already include an automatic altitude correction

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A condensate drain line is installed dead level for a long run and plugs with slime every season. What installation defect is most likely?

The line was made from approved drain material instead of thin-wall tubing that stays warmer and therefore resists biological growth

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The drain terminates at an approved receptor instead of discharging directly onto the roof membrane below the condensing unit

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The trap was installed at the unit rather than at the far end of the run near the floor drain, where traps are most effective

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The line lacks continuous downward slope in the direction of flow.

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A variable-speed drive slows a chilled-water pump to 90% of full speed. Using the pump affinity laws, about how much pump power is saved?

About 3%, because pump power falls only in direct one-to-one proportion to the drop in pump rotational speed

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About 10%, because pump power falls in proportion to the square of the speed ratio at reduced flow conditions

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About 19%, because pump head and pump power always change by exactly the same percentage as each other

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About 27%, because power varies with the cube of speed: 0.9 cubed is about 0.73 of full power

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A gas furnace in Bear lights its burners on every call for heat, but the burners shut off again after only a few seconds, cycle after cycle, while the inducer keeps running normally. The flame sensor rod is visibly coated with a white oxide film. What is the most likely cause?

The coated sensor cannot pass an adequate flame-rectification signal to the control, so the board shuts the gas valve down when it fails to prove flame

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The oxide film makes the sensor read too much flame current, so the board opens the valve wider until the high limit trips the burners off, after which the board advances the inducer to high speed and holds the furnace in a permanent heating lockout

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The flame sensor controls the inducer motor speed, and its coating has slowed the inducer below the pressure switch setpoint

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The coating insulates the sensor so well that the board believes the heat exchanger is overheated and locks the furnace out for one hour

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Delaware HVAC Exam Prep FREE Sample Exam — Fixed Set

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