108 questions
The nameplate of a condensing unit lists a maximum overcurrent protection of 35 amps and a minimum circuit ampacity of 22 amps. How should the circuit be built?
- a.Conductors rated at least 22 amps, protected at no more than 35 amps✓
- b.Conductors and breaker both sized to exactly 35 amps
- c.Conductors rated at least 35 amps, protected at 22 amps
- d.Conductors sized to 22 amps with a 60 amp breaker for starting surge
Minimum circuit ampacity sets the conductor size and maximum overcurrent protection caps the breaker, so 22-amp conductors on a breaker no larger than 35 amps is correct. Sizing conductors to the breaker rating and then undersizing the breaker inverts both values. Forcing both to 35 amps ignores the ampacity figure the manufacturer calculated. And a 60-amp breaker exceeds the listed maximum and would not protect the equipment.
A technician finds the new furnace's blower rotating backwards after wiring the three-phase supply to a commercial air handler. What is the fix?
- a.Reverse the low-voltage thermostat wires at the terminal board
- b.Replace the motor with one rated for the opposite rotation
- c.Swap any two of the three line conductors at the disconnect✓
- d.Rewire the motor's internal windings for the other direction
Three-phase rotation is determined by phase sequence, so interchanging any two line conductors reverses the motor. Control wiring does not set rotation direction. Opening a motor to rewire internal windings is not a field procedure for phase rotation. And replacing a perfectly good motor is unnecessary when the correction is a two-wire swap at the disconnect.
A new furnace is installed and the temperature rise measures 30 F against a rating plate range of 40 to 70 F. What adjustment is appropriate?
- a.Reduce blower speed until the rise falls inside the listed range✓
- b.Increase the manifold gas pressure above the rated value
- c.Replace the limit switch with one rated for a lower setpoint
- d.Add restriction at the return duct to raise the system static pressure
Too low a rise means the blower is moving more air than the burner output warrants, so slowing the blower brings the rise into range. Overfiring the burner past its rated manifold pressure is unsafe and voids the listing. Deliberately restricting the return raises static and stresses the blower rather than properly setting speed. And changing the limit switch masks an airflow setting problem while removing a safety margin.
How is manifold gas pressure on a new natural gas furnace verified at startup?
- a.By measuring inlet pressure at the gas valve during standby
- b.By counting the gas meter dial revolutions over one minute
- c.By reading the pressure at the meter with all appliances off
- d.By connecting a manometer to the valve's outlet tap with the burner firing✓
Manifold pressure is measured at the outlet tap of the gas valve while the burner runs, and compared against the rating plate value. Meter pressure with appliances off shows static supply pressure, not manifold pressure. Inlet pressure during standby tells you the supply is present but not what the burner is receiving. And clocking the meter measures input rate, which is a related but separate check.
A high-efficiency furnace is vented through a sidewall. Which termination concern is most important?
- a.Keeping the vent and intake at exactly the same elevation
- b.Maintaining required separation from windows, doors, and air intakes✓
- c.Terminating below grade level so the plume is not visible
- d.Sloping the vent downward so condensate drains out through the terminal
Sidewall terminations must be far enough from openings and intakes that flue gas is not drawn back into the building. Concentric and two-pipe terminations follow the manufacturer's spacing rather than a rule that both be at the same height. The vent slopes back toward the furnace so condensate drains to the appliance, not out the terminal. And terminating below grade invites blockage by snow, leaves, and standing water.
A condensing furnace's condensate is being routed to a drain. Why is a neutralizer sometimes installed?
- a.To filter out combustion particulate before it reaches the sewer line
- b.Because the condensate is acidic and can attack metal drain piping✓
- c.To reduce the volume of condensate produced
- d.To keep the condensate warm enough to prevent freezing
Flue gas condensate is mildly acidic, and a neutralizer raises its pH so it does not corrode metallic drain lines or violate local discharge rules. Nothing about a neutralizer changes how much condensate the appliance makes. It has no heating function and does not prevent freezing. And it is a chemical treatment, not a particulate filter.
A residential air handler is installed in a closet with louvered doors and no dedicated return duct. What problem does this create?
- a.The blower will be starved because louvers restrict airflow
- b.The closet will be pressurized, forcing air into the wall cavities
- c.Return air is drawn from the closet and whatever leaks into it, bypassing the filter path✓
- d.The equipment cannot be serviced because the doors must remain closed
Using the closet itself as a return plenum pulls air from wall cavities, the attic, and any adjacent unconditioned space, which defeats filtration and duct leakage control. Louvers are usually generous enough that raw restriction is not the primary failure. The closet goes negative on the return side, not positive. And serviceability is a separate concern that door louvers do not create.
When is a mechanical permit generally required for HVAC work in California?
- a.Only when the equipment capacity increases over the original
- b.Only for commercial buildings, since dwellings are exempt
- c.Only when the building's electrical service is also being upgraded at the same time
- d.For installation, replacement, or alteration of equipment and duct systems✓
Local jurisdictions require a mechanical permit for installing, replacing, or altering regulated equipment and ductwork, regardless of building type. Electrical work has its own permit and is not the trigger for the mechanical one. Dwellings are squarely covered by the mechanical code. And a like-for-like change-out still requires a permit even when capacity does not change.California Mechanical Code (Title 24, Part 4)